Particle physics or high-energy physics is the study of fundamental particles and forces that constitute matter and radiation. The field also studies combinations of elementary particles up to the scale of protons and neutrons, while the study of combinations of protons and neutrons is called nuclear physics. The fundamental particles in the universe are classified in the Standard Model as fermions (matter particles) and bosons (force-carrying particles). There are three generations of fermions, although ordinary matter is made only from the first fermion generation. The first generation consists of up and down quarks which form protons and neutrons, and electrons and electron neutrinos. The three fundamental interactions known to be mediated by bosons are electromagnetism, the weak interaction, and the strong interaction. Quarks form hadrons, but cannot exist on their own. Hadrons that contain an odd number of quarks are called baryons and those that contain an even number are called mesons. Two baryons, the proton and the neutron, make up most of the mass of ordinary matter. Mesons are unstable and the longest-lived last for only a few hundredths of a microsecond. They occur after collisions between particles made of quarks, such as fast-moving protons and neutrons in cosmic rays. Mesons are also produced in cyclotrons or other particle accelerators. Particles have corresponding antiparticles with the same mass but with opposite electric charges. For example, the antiparticle of the electron is the positron. The electron has a negative electric charge, the positron has a positive charge. These antiparticles can theoretically form a corresponding form of matter called antimatter. Some particles, such as the photon, are their own antiparticle. These elementary particles are excitations of the quantum fields that also govern their interactions. The dominant theory explaining these fundamental particles and fields, along with their dynamics, is called the Standard Model. The reconciliation of gravity to the current particle physics theory is not solved; many theories have addressed this problem, such as loop quantum gravity, string theory and supersymmetry theory. Experimental particle physics is the study of these particles in radioactive processes and in particle accelerators such as the Large Hadron Collider. Theoretical particle physics is the study of these particles in the context of cosmology and quantum theory. The two are closely interrelated: the Higgs boson was postulated theoretically before being confirmed by experiments. History Main article: History of subatomic physics see caption The Geiger–Marsden experiments observed that a small fraction of the alpha particles experienced strong deflection when being struck by the gold foil. The idea that all matter is fundamentally composed of elementary particles dates from at least the 6th century BC.[1] In the 19th century, John Dalton, through his work on stoichiometry, concluded that each element of nature was composed of a single, unique type of particle.[2] The word atom, after the Greek word atomos meaning "indivisible", has since then denoted the smallest particle of a chemical element, but physicists later discovered that atoms are not, in fact, the fundamental particles of nature, but are conglomerates of even smaller particles, such as the electron. The early 20th century explorations of nuclear physics and quantum physics led to proofs of nuclear fission in 1939 by Lise Meitner (based on experiments by Otto Hahn), and nuclear fusion by Hans Bethe in that same year; both discoveries also led to the development of nuclear weapons. Bethe's 1947 calculation of the Lamb shift is credited with having "opened the way to the modern era of particle physics".[3] Throughout the 1950s and 1960s, a bewildering variety of particles was found in collisions of particles from beams of increasingly high energy. It was referred to informally as the "particle zoo". Important discoveries such as the CP violation by James Cronin and Val Fitch brought new questions to matter-antimatter imbalance.[4] After the formulation of the Standard Model during the 1970s, physicists clarified the origin of the particle zoo. The large number of particles was explained as combinations of a (relatively) small number of more fundamental particles and framed in the context of quantum field theories. This reclassification marked the beginning of modern particle physics.[5][6] Standard Model Main article: Standard Model The current state of the classification of all elementary particles is explained by the Standard Model, which gained widespread acceptance in the mid-1970s after experimental confirmation of the existence of quarks. It describes the strong, weak, and electromagnetic fundamental interactions, using mediating gauge bosons. The species of gauge bosons are eight gluons, W− , W+ and Z bosons, and the photon.[7] The Standard Model also contains 24 fundamental fermions (12 particles and their associated anti-particles), which are the constituents of all matter.[8] Finally, the Standard Model also predicted the existence of a type of boson known as the Higgs boson. On 4 July 2012, physicists with the Large Hadron Collider at CERN announced they had found a new particle that behaves similarly to what is expected from the Higgs boson.[9] The Standard Model, as currently formulated, has 61 elementary particles.[10] Those elementary particles can combine to form composite particles, accounting for the hundreds of other species of particles that have been discovered since the 1960s. The Standard Model has been found to agree with almost all the experimental tests conducted to date. However, most particle physicists believe that it is an incomplete description of nature and that a more fundamental theory awaits discovery (See Theory of Everything). In recent years, measurements of neutrino mass have provided the first experimental deviations from the Standard Model, since neutrinos do not have mass in the Standard Model.[11] Subatomic particles Modern particle physics research is focused on subatomic particles, including atomic constituents, such as electrons, protons, and neutrons (protons and neutrons are composite particles called baryons, made of quarks), that are produced by radioactive and scattering processes; such particles are photons, neutrinos, and muons, as well as a wide range of exotic particles.[12] All particles and their interactions observed to date can be described almost entirely by the Standard Model.[7] Elementary Particles Types Generations Antiparticle Colours Total Quarks 2 3 Pair 3 36 Leptons Pair None 12 Gluons 1 None Own 8 8 Photon Own None 1 Z Boson Own 1 W Boson Pair 2 Higgs Own 1 Total number of (known) elementary particles: 61 Dynamics of particles are also governed by quantum mechanics; they exhibit wave–particle duality, displaying particle-like behaviour under certain experimental conditions and wave-like behaviour in others. In more technical terms, they are described by quantum state vectors in a Hilbert space, which is also treated in quantum field theory. Following the convention of particle physicists, the term elementary particles is applied to those particles that are, according to current understanding, presumed to be indivisible and not composed of other particles.[10] Quarks and leptons Main articles: Quark and Lepton A Feynman diagram of the β− decay, showing a neutron (n, udd) converted into a proton (p, udu). "u" and "d" are the up and down quarks, "e− " is the electron, and "ν e" is the electron antineutrino. Ordinary matter is made from first-generation quarks (up, down) and leptons (electron, electron neutrino).[13] Collectively, quarks and leptons are called fermions. They have a quantum spin of half-integers (−1/2, 1/2, 3/2, etc.) and obey the Pauli exclusion principle, where no two particles may occupy the same quantum state.[14] Quarks have fractional elementary electric charge (−1/3 or 2/3)[15] and leptons have whole-numbered electric charge (0 or -1).[16] Quarks also have color charge, which is labeled arbitrarily with no correlation to actual light color as red, green and blue.[17] Because the interactions between the quarks store energy which can convert to other particles when the quarks are far apart enough, quarks cannot be observed independently. This is called color confinement.[17] There are three known generations of quarks (up and down, strange and charm, top and bottom) and leptons (electron and its neutrino, muon and its neutrino, tau and its neutrino), with strong indirect evidence that a fourth generation of fermions does not exist.[18] Bosons Main article: Boson Bosons are the mediators or carriers of fundamental interactions, such as electromagnetism, the weak interaction, and the strong interaction.[19] Electromagnetism is mediated by the photon, the quanta of light.[20]: 29–30 The weak interaction is mediated by the W and Z bosons.[21] The strong interaction is mediated by the gluon, which can link quarks together to form composite particles.[22] Due to the aforementioned color confinement, gluons are never observed independently.[23] The Higgs boson gives mass to the W and Z bosons via the Higgs mechanism[24] – the gluon and photon are expected to be massless.[23] All bosons have an integer quantum spin (0 and 1) and can have the same quantum state.[19] Antiparticles and color charge Main articles: Antiparticle and Color charge Most aforementioned particles have corresponding antiparticles, which compose antimatter. Normal particles have positive lepton or baryon number, and antiparticles have these numbers negative.[25] Most properties of corresponding antiparticles and particles are the same, with a few gets reversed; the electron's antiparticle, positron, has an opposite charge. To differentiate between antiparticles and particles, a plus or negative sign is added in superscript. For example, the electron and the positron are denoted e− and e+ , respectively.[26] However, in the case that the particle has a charge of 0 (equal to that of the antiparticle), the antiparticle is denoted with a line above the symbol. As such, an electron neutrino is ν e, whereas its antineutrino is ν e. When a particle and an antiparticle interact with each other, they are annihilated and convert to other particles.[27] Some particles, such as the photon or gluon, have no antiparticles.[citation needed] Quarks and gluons additionally have color charges, which influences the strong interaction. Quark's color charges are called red, green and blue (though the particle itself have no physical color), and in antiquarks are called antired, antigreen and antiblue.[17] The gluon can have eight color charges, which are the result of quarks' interactions to form composite particles (gauge symmetry SU(3)).[28] Composite Main article: Composite particle A proton consists of two up quarks and one down quark, linked together by gluons. The quarks' color charge are also visible. The neutrons and protons in the atomic nuclei are baryons – the neutron is composed of two down quarks and one up quark, and the proton is composed of two up quarks and one down quark.[29] A baryon is composed of three quarks, and a meson is composed of two quarks (one normal, one anti). Baryons and mesons are collectively called hadrons. Quarks inside hadrons are governed by the strong interaction, thus are subjected to quantum chromodynamics (color charges). The bounded quarks must have their color charge to be neutral, or "white" for analogy with mixing the primary colors.[30] More exotic hadrons can have other types, arrangement or number of quarks (tetraquark, pentaquark).[31] An atom is made from protons, neutrons and electrons.[32] By modifying the particles inside a normal atom, exotic atoms can be formed.[33] A simple example would be the hydrogen-4.1, which has one of its electrons replaced with a muon.[34] Hypothetical The graviton is a hypothetical particle that can mediate the gravitational interaction, but it has not been detected or completely reconciled with current theories.[35] Many other hypothetical particles have been proposed to address the limitations of the Standard Model. Notably, supersymmetric particles aim to solve the hierarchy problem, axions address the strong CP problem, and various other particles are proposed to explain the origins of dark matter and dark energy. Experimental laboratories Fermi National Accelerator Laboratory, USA The world's major particle physics laboratories are: Brookhaven National Laboratory (Long Island, New York, United States). Its main facility is the Relativistic Heavy Ion Collider (RHIC), which collides heavy ions such as gold ions and polarized protons. It is the world's first heavy ion collider, and the world's only polarized proton collider.[36][37] Budker Institute of Nuclear Physics (Novosibirsk, Russia). Its main projects are now the electron-positron colliders VEPP-2000,[38] operated since 2006, and VEPP-4,[39] started experiments in 1994. Earlier facilities include the first electron–electron beam–beam collider VEP-1, which conducted experiments from 1964 to 1968; the electron-positron colliders VEPP-2, operated from 1965 to 1974; and, its successor VEPP-2M,[40] performed experiments from 1974 to 2000.[41] CMS detector for LHC CERN (European Organization for Nuclear Research) (Franco-Swiss border, near Geneva, Switzerland). Its main project is now the Large Hadron Collider (LHC), which had its first beam circulation on 10 September 2008, and is now the world's most energetic collider of protons. It also became the most energetic collider of heavy ions after it began colliding lead ions. Earlier facilities include the Large Electron–Positron Collider (LEP), which was stopped on 2 November 2000 and then dismantled to give way for LHC; and the Super Proton Synchrotron, which is being reused as a pre-accelerator for the LHC and for fixed-target experiments.[42] DESY (Deutsches Elektronen-Synchrotron) (Hamburg, Germany). Its main facility was the Hadron Elektron Ring Anlage (HERA), which collided electrons and positrons with protons.[43] The accelerator complex is now focused on the production of synchrotron radiation with PETRA III, FA mental disorder, also referred to as a mental illness,[6] a mental health condition,[7] or a psychiatric disability,[2] is a behavioral or mental pattern that causes significant distress or impairment of personal functioning.[8] A mental disorder is also characterized by a clinically significant disturbance in an individual's cognition, emotional regulation, or behavior, often in a social context.[9][10] Such disturbances may occur as single episodes, may be persistent, or may be relapsing–remitting. There are many different types of mental disorders, with signs and symptoms that vary widely between specific disorders.[10][11] A mental disorder is one aspect of mental health. The causes of mental disorders are often unclear. Theories incorporate findings from a range of fields. Disorders may be associated with particular regions or functions of the brain. Disorders are usually diagnosed or assessed by a mental health professional, such as a clinical psychologist, psychiatrist, psychiatric nurse, or clinical social worker, using various methods such as psychometric tests, but often relying on observation and questioning. Cultural and religious beliefs, as well as social norms, should be taken into account when making a diagnosis.[12] Services for mental disorders are usually based in psychiatric hospitals, outpatient clinics, or in the community (in the United Kingdom). Treatments are provided by mental health professionals. Common treatment options are psychotherapy or psychiatric medication, while lifestyle changes, social interventions, peer support, and self-help are also options. In a minority of cases, there may be involuntary detention or treatment. Prevention programs have been shown to reduce depression.[10][13] In 2019, common mental disorders around the globe include: major depression, which affects about 264 million people; dementia, which affects about 50 million; bipolar disorder, which affects about 45 million; and schizophrenia and other psychoses, which affect about 20 million people.[10] Neurodevelopmental disorders include attention deficit hyperactivity disorder (ADHD), autism spectrum disorder (autism), and intellectual disability, of which onset occurs early in the developmental period.[14][10] Stigma and discrimination can add to the suffering and disability associated with mental disorders, leading to various social movements attempting to increase understanding and challenge social exclusion. Definition "Nervous breakdown" redirects here. For other uses, see Nervous breakdown (disambiguation). The definition and classification of mental disorders are key issues for researchers as well as service providers and those who may be diagnosed. For a mental state to be classified as a disorder, it generally needs to cause dysfunction.[15] Most international clinical documents use the term mental "disorder", while "illness" is also common. It has been noted that using the term "mental" (i.e., of the mind) is not necessarily meant to imply separateness from the brain or body. According to the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), published in 1994, a mental disorder is a psychological syndrome or pattern that is associated with distress (e.g., via a painful symptom), disability (impairment in one or more important areas of functioning), increased risk of death, or causes a significant loss of autonomy; however, it excludes normal responses such as the grief from loss of a loved one and also excludes deviant behavior for political, religious, or societal reasons not arising from a dysfunction in the individual.[16] The DSM-IV definition states that, like many medical terms, mental disorder "lacks a consistent operational definition that covers all situations". It notes that different levels of abstraction can be used for medical definitions, including pathology, symptomology, deviance from a normal range, or etiology, and that the same is true for mental disorders, so that sometimes one type of definition is appropriate and sometimes another, depending on the situation.[17] In 2013, the American Psychiatric Association (APA) redefined mental disorders in the DSM-5 as "a syndrome characterized by clinically significant disturbance in an individual's cognition, emotion regulation, or behavior that reflects a dysfunction in the psychological, biological, or developmental processes underlying mental functioning."[18] The final draft of ICD-11 contains a very similar definition.[19] The terms "mental breakdown" or "nervous breakdown" may be used by the general population to mean a mental disorder.[20] The terms "nervous breakdown" and "mental breakdown" have not been formally defined through a medical diagnostic system such as the DSM-5 or ICD-10 and are nearly absent from scientific literature regarding mental illness.[21][22] Although "nervous breakdown" is not rigorously defined, surveys of laypersons suggest that the term refers to a specific acute time-limited reactive disorder involving symptoms such as anxiety or depression, usually precipitated by external stressors.[21] Many health experts today refer to a nervous breakdown as a mental health crisis.[23] Nervous illness This article contains too many or overly lengthy quotations. Please help summarize the quotations. Consider transferring direct quotations to Wikiquote or excerpts to Wikisource. (February 2026) (Learn how and when to remove this message) In addition to the concept of mental disorder, some people have argued for a return to the old-fashioned concept of nervous illness. In How Everyone Became Depressed: The Rise and Fall of the Nervous Breakdown (2013), Edward Shorter, a professor of psychiatry and the history of medicine, says: We have had nervous illness for centuries. When you are too nervous to function ... it is a nervous breakdown. But that term has vanished from medicine, although not from the way we speak.... The nervous patients of yesteryear are the depressives of today. That is the bad news.... There is a deeper illness that drives depression and the symptoms of mood. We can call this deeper illness something else, or invent a neologism, but we need to get the discussion off depression and onto this deeper disorder in the brain and body. That is the point. — Edward Shorter, the University of Toronto[24] In eliminating the nervous breakdown, psychiatry has come close to having its own nervous breakdown. — David Healy, MD, FRCPsych, Professor of Psychiatry, University of Cardiff, Wales[25] Nerves stand at the core of common mental illness, no matter how much we try to forget them. — Peter J. Tyrer, FMedSci, Professor of Community Psychiatry, Imperial College, London[26] Classifications Main article: Classification of mental disorders There are currently two widely established systems that classify mental disorders: International Classification of Diseases produced by the WHO. The latest edition is the ICD-11, which is in effect since 1 January 2022.[27] The ICD is a broad medical classification system; mental disorders are contained in Chapter 06: Mental, behavioural or neurodevelopmental disorders (06). Diagnostic and Statistical Manual of Mental Disorders produced by the American Psychiatric Association since 1952. The latest edition is the Fifth Edition, Text Revision (DSM-5-TR), which was released in 2022.[28] Both of these list categories of disorder and provide standardized criteria for diagnosis. They have deliberately converged their codes in recent revisions so that the manuals are often broadly comparable, although significant differences remain. Other classification schemes may be used in non-western cultures, for example, the Chinese Classification of Mental Disorders, and other manuals may be used by those of alternative theoretical persuasions, such as the Psychodynamic Diagnostic Manual. In general, mental disorders are classified separately from neurological disorders, learning disabilities or intellectual disability. Unlike the DSM and ICD, some approaches are not based on identifying distinct categories of disorder using dichotomous symptom profiles intended to separate the abnormal from the normal. There is significant scientific debate about the relative merits of categorical versus such non-categorical (or hybrid) schemes, also known as continuum or dimensional models. A spectrum approach may incorporate elements of both. In the scientific and academic literature on the definition or classification of mental disorder, one extreme argues that it is entirely a matter of value judgements (including of what is normal) while another proposes that it is or could be entirely objective and scientific (including by reference to statistical norms).[29] Common hybrid views argue that the concept of mental disorder is objective even if only a "fuzzy prototype" that can never be precisely defined, or conversely that the concept always involves a mixture of scientific facts and subjective value judgments.[30] Although the diagnostic categories are referred to as 'disorders', they are presented as medical diseases, but are not validated in the same way as most medical diagnoses. Some neurologists argue that classification will only be reliable and valid when based on neurobiological features rather than clinical interview, while others suggest that the differing ideological and practical perspectives need to be better integrated.[31][32] The DSM and ICD approach remains under attack both because of the implied causality model[33] and because some researchers believe it better to aim at underlying brain differences which can precede symptoms by many years.[34] Dimensional models The high degree of comorbidity between disorders in categorical models such as the DSM and ICD have led some to propose dimensional models. Studying comorbidity between disorders have demonstrated two latent (unobserved) factors or dimensions in the structure of mental disorders that are thought to possibly reflect etiological processes. These two dimensions reflect a distinction between internalizing disorders, such as mood or anxiety symptoms, and externalizing disorders such as behavioral or substance use symptoms.[35] A single general factor of psychopathology, similar to the g factor for intelligence, has been empirically supported. The p factor model supports the internalizing-externalizing distinction, but also supports the formation of a third dimension of thought disorders such as schizophrenia.[36] Biological evidence also supports the validity of the internalizing-externalizing structure of mental disorders, with twin and adoption studies supporting heritable factors for externalizing and internalizing disorders.[37][38][39] A leading dimensional model is the Hierarchical Taxonomy of Psychopathology. Disorders See also: List of mental disorders There are many different categories of mental disorder, and many different facets of human behavior and personality that can become disordered.[40][41][42][43] Anxiety disorders Main article: Anxiety disorder An anxiety disorder is anxiety or fear that interferes with normal functioning.[41] Commonly recognized categories include specific phobias, generalized anxiety disorder, social anxiety disorder, panic disorder, agoraphobia, and post-traumatic stress disorder. Obsessive–compulsive disorder was categorized as an anxiety disorder in DSM-III, which was published in 1980, but was later placed in its own section called "Obsessive-Compulsive and Related Disorder" in DSM-5.[44] Mood disorders Main article: Mood disorder Other affective (emotion/mood) processes can also become disordered. Mood disorder involving unusually intense and sustained sadness, melancholia, or despair is known as major depression (also known as unipolar or clinical depression). Milder, but still prolonged depression, can be diagnosed as dysthymia. Bipolar disorder (also known as manic depression) involves abnormally "high" or pressured mood states, known as mania or hypomania, alternating with normal or depressed moods. The extent to which unipolar and bipolar mood phenomena represent distinct categories of disorder, or mix and merge along a dimension or spectrum of mood, is subject to some scientific debate.[45][46] Psychotic disorders Main article: Psychotic disorder Patterns of belief, language use and perception of reality can become dysregulated (e.g., delusions, thought disorder, hallucinations). Psychotic disorders in this domain include schizophrenia, and delusional disorder. Schizoaffective disorder is a category used for individuals showing aspects of both schizophrenia and affective disorders. Schizotypy is a category used for individuals showing some of the characteristics associated with schizophrenia, but without meeting cutoff criteria.[citation needed] Personality disorders Main article: Personality disorder Personality—the fundamental characteristics of a person that influence thoughts and behaviors across situations and time—may be considered disordered if judged to be abnormally rigid and maladaptive. Although treated separately by some[by whom?], the commonly used categorical schemes[which?] include them as mental disorders. Personality disorders, in general, are defined as emerging in childhood, or at least by adolescence or early adulthood. There is an emerging consensus that personality disorders, similar to personality traits in general, incorporate a mixture of acute dysfunctional behaviors that may resolve in short periods, and maladaptive temperamental traits that are more enduring.[47] Furthermore, there are also non-categorical schemes that rate all individuals via a profile of different dimensions of personality without a symptom-based cutoff from normal personality variation, for example through schemes based on dimensional models of personality disorders.[48][49][non-primary source needed] A number of different personality disorders are listed in the DSM-5-TR, including those sometimes classed as eccentric, such as paranoid, schizoid and schizotypal personality disorders; types that have described as dramatic or emotional, such as antisocial, borderline, histrionic or narcissistic personality disorders; and those sometimes classed as fear-related, such as anxious-avoidant, dependent, or obsessive–compulsive personality disorders.[citation needed] While the DSM-5-TR standard model diagnoses personality disorders as distinct categories, the ICD-11 classification of personality disorders contains a single, dimensional personality disorder which is diagnosed according to severity, with the possibility to additionally diagnose trait domains.[50] In the case of the Alternative DSM-5 Model for Personality disorders, the approach chosen is a dimensional–categorical model,[51] in which diagnosis can consist of either predefined categories based on specific combinations of traits and functioning levels,[52] or of a general diagnosis called personality disorder – trait specified.[52] The ICD-11 classifies schizotypal disorder among primary psychotic disorders rather than as a personality disorder as in the DSM-5.[53] Neurodevelopmental disorders Main article: Neurodevelopmental disorder Neurodevelopmental disorders are a group of mental disorders that affect the central nervous system, such as the brain and spinal cord.[54] These disorders can appear in early childhood.[55] They can even persist into adulthood.[56] A few of the common are attention deficit hyperactivity disorder (ADHD), autism spectrum disorder (autism), intellectual disabilities, motor disorders, and communication disorders among others. Some causes can contribute to these disorders, such as genetic factors (genetics, family medical history),[57] environmental factors (excessive stress, exposure to neurotoxins, pollution, viral infections, bacterial infections),[58][59] physical factors (traumatic brain injury, illness),[60] and prenatal factors (birth defects, exposure to drugs during pregnancy, low birth weight).[61] Neurodevelopmental disorders can be managed with behavioral therapy, applied behavior analysis (ABA), educational interventions, specific medications, and other such treatments.[62] Approximately 8 in 10 people with autism suffer from a mental health problem in their lifetime, in comparison to 1 in 4 of the general population that suffers from a mental health problem in their lifetimes.[63][64][65] Eating disorders Main article: Eating disorder An eating disorder is a serious mental health condition that involves an unhealthy relationship with food and body image. They can cause severe physical and psychological problems.[66] Eating disorders involve disproportionate concern in matters of food and weight.[41] Categories eating disorders include anorexia nervosa, bulimia nervosa, exercise bulimia, or binge eating disorder.[67][68] Sleep disorders Main article: Sleep disorder Sleep disorders are associated with disruption to normal sleep patterns. A common sleep disorder is insomnia, which is described as difficulty falling and/or staying asleep. Other sleep disorders include narcolepsy, sleep apnea, REM sleep behavior disorder, chronic sleep deprivation, and restless leg syndrome. Narcolepsy is a condition of extreme tendencies to fall asleep whenever and wherever. People with narcolepsy feel refreshed after their random sleep, but eventually get sleepy again. Narcolepsy diagnosis requires an overnight stay at a sleep center for analysis, during which doctors ask for a detailed sleep history and sleep records. Doctors also use actigraphs and polysomnography.[69] Doctors will do a multiple sleep latency test, which measures how long it takes a person to fall asleep.[69] Sleep apnea, when breathing repeatedly stops and starts during sleep, can be a serious sleep disorder. Three types of sleep apnea include obstructive sleep apnea, central sleep apnea, and complex sleep apnea.[70] Sleep apnea can be diagnosed at home or with polysomnography at a sleep center. An ear, nose, and throat doctor may further help with the sleeping habits. Sexuality related Sexual disorders include dyspareunia and various kinds of paraphilia (sexual arousal to objects, situations, or individuals that are considered abnormal or harmful to the person or others).[citation needed] Other Impulse control disorders: People who are abnormally unable to resist certain urges or impulses that could be harmful to themselves or others, may be classified as having an impulse control disorder, and disorders such as kleptomania (stealing) or pyromania (fire-setting). Various behavioral addictions, such as gambling addiction, may be classed as a disorder.[citation needed] Substance use disorders: This disorder refers to the use of drugs (legal or illegal, including alcohol) that persists despite significant problems or harm related to its use. Substance dependence and substance abuse fall under this umbrella category in the DSM. Substance use disorder may be due to a pattern of compulsive and repetitive use of a drug that results in tolerance to its effects and withdrawal symptoms when use is reduced or stopped.[citation needed] Dissociative disorders: People with severe disturbances of their self-identity, memory, and general awareness of themselves and their surroundings may be classified as having these types of disorders, including depersonalization-derealization disorder or dissociative identity disorder (which was previously referred to as multiple personality disorder or "split personality").[citation needed] Cognitive disorders: These affect cognitive abilities, including learning and memory. This category includes delirium and mild and major neurocognitive disorder (previously termed dementia).[citation needed] Somatoform disorders may be diagnosed when there are problems that appear to originate in the body that are thought to be manifestations of a mental disorder. This includes somatization disorder and conversion disorder. There are also disorders of how a person perceives their body, such as body dysmorphic disorder. Neurasthenia is an old diagnosis involving somatic complaints as well as fatigue and low spirits/depression, which is officially recognized by the ICD-10 but no longer by the DSM-IV.[71][non-primary source needed] Factitious disorders are diagnosed where symptoms are thought to be reported for personal gain. Symptoms are often deliberately produced or feigned, and may relate to either symptoms in the individual or in someone close to them, particularly people they care for.[citation needed] There are attempts to introduce a category of relational disorder, where the diagnosis is of a relationship rather than on any one individual in that relationship. The relationship may be between children and their parents, between couples, or others. There already exists, under the category of psychosis, a diagnosis of shared psychotic disorder where two or more individuals share a particular delusion because of their close relationship with each other.[citation needed] There are a number of uncommon psychiatric syndromes, which are often named after the person who first described them, such as Capgras syndrome, De Clerambault syndrome, Othello syndrome, Ganser syndrome, Cotard delusion, and Ekbom syndrome, and additional disorders such as the Couvade syndrome and Geschwind syndrome.[72] Signs and symptoms Course The onset of psychiatric disorders usually occurs from childhood to early adulthood.[73] Impulse-control disorders and a few anxiety disorders tend to appear in childhood. Some other anxiety disorders, substance disorders, and mood disorders emerge later in the mid-teens.[74] Symptoms of schizophrenia typically manifest from late adolescence to early twenties.[75] The likely course and outcome of mental disorders vary and are dependent on numerous factors related to the disorder itself, the individual as a whole, and the social environment. Some disorders may last a brief period of time, while others may be long-term in nature. All disorders can have a varied course. Long-term international studies of schizophrenia have found that over a half of individuals recover in terms of symptoms, and around a fifth to a third in terms of symptoms and functioning, with many requiring no medication. While some have serious difficulties and support needs for many years, "late" recovery is still plausible. The World Health Organization (WHO) concluded that the long-term studies' findings converged with others in "relieving patients, carers and clinicians of the chronicity paradigm which dominated thinking throughout much of the 20th century."[76][non-primary source needed][77] A follow-up study by Tohen and coworkers revealed that around half of people initially diagnosed with bipolar disorder achieve symptomatic recovery (no longer meeting criteria for the diagnosis) within six weeks, and nearly all achieve it within two years, with nearly half regaining their prior occupational and residential status in that period. Less than half go on to experience a new episode of mania or major depression within the next two years.[78][non-primary source needed] Disability Disorder Disability-adjusted life years[79] Major depressive disorder 65.5 million Alcohol-use disorder 23.7 million Schizophrenia 16.8 million Bipolar disorder 14.4 million Other drug-use disorders 8.4 million Panic disorder 7.0 million Obsessive-compulsive disorder 5.1 million Primary insomnia 3.6 million Post-traumatic stress disorder 3.5 million Some disorders may be very limited in their functional effects, while others may involve substantial disability and support needs. In this context, the terms psychiatric disability and psychological disability are sometimes used instead of mental disorder.[2][3] The degree of ability or disability may vary over time and across different life domains. Furthermore, psychiatric disability has been linked to institutionalization, discrimination and social exclusion as well as to the inherent effects of disorders. Alternatively, functioning may be affected by the stress of having to hide a condition in work or school, etc., by adverse effects of medications or other substances, or by mismatches between illness-related variations and demands for regularity.[80] It is also the case that, while often being characterized in purely negative terms, some mental traits or states labeled as psychiatric disabilities can also involve above-average creativity, non-conformity, goal-striving, meticulousness, or empathy.[81] In addition, the public perception of the level of disability associated with mental disorders can change.[82] Nevertheless, internationally, people report equal or greater disability from commonly occurring mental conditions than from commonly occurring physical conditions, particularly in their social roles and personal relationships. The proportion with access to professional help for mental disorders is far lower, however, even among those assessed as having a severe psychiatric disability.[83] Disability in this context may or may not involve such things as: Basic activities of daily living. Including looking after the self (health care, grooming, dressing, shopping, cooking etc.) or looking after accommodation (chores, DIY tasks, etc.) Interpersonal relationships. Including communication skills, ability to form relationships and sustain them, ability to leave the home or mix in crowds or particular settings Occupational functioning. Ability to acquire an employment and hold it, cognitive and social skills required for the job, dealing with workplace culture, or studying as a student. In terms of total disability-adjusted life years (DALYs), which is an estimate of how many years of life are lost due to premature death or to being in a state of poor health and disability, psychiatric disabilities rank amongst the most disabling conditions. Unipolar depressive disorder (also known as major depressive disorder) is the third leading cause of disability worldwide, of any condition mental or physical, accounting for 65.5 million years lost. The first systematic description of global disability arising in youth, in 2011, found that among 10- to 24-year-olds nearly half of all disability (current and as estimated to continue) was due to psychiatric disabilities, including substance use disorders and conditions involving self-harm. Second to this were accidental injuries (mainly traffic collisions) accounting for 12 percent of disability, followed by communicable diseases at 10 percent. The psychiatric disabilities associated with most disabilities in high-income countries were unipolar major depression (20%) and alcohol use disorder (11%). In the eastern Mediterranean region, it was unipolar major depression (12%) and schizophrenia (7%), and in Africa it was unipolar major depression (7%) and bipolar disorder (5%).[84] Suicide, which is often attributed to some underlying mental disorder, is a leading cause of death among teenagers and adults under 35.[85][86] There are an estimated 10 to 20 million non-fatal attempted suicides every year worldwide.[87] Risk factors Main article: Causes of mental disorders The predominant view as of 2018 is that genetic, psychological, and environmental factors all contribute to the development or progression of mental disorders.[88] Different risk factors may be present at different ages, with risk occurring as early as during prenatal period.[89] Genetics Main article: Psychiatric genetics A number of psychiatric disorders are linked to a family history (including depression, narcissistic personality disorder[90][91] and anxiety).[92] Twin studies have also revealed a very high heritability for many mental disorders (especially autism and schizophrenia).[93] Although researchers have been looking for decades for clear linkages between genetics and mental disorders, that work has not yielded specific genetic biomarkers yet that might lead to better diagnosis and better treatments.[94] Statistical research looking at eleven disorders found widespread assortative mating between people with mental illness. That means that individuals with one of these disorders were two to three times more likely than the general population to have a partner with a mental disorder. Sometimes people seemed to have preferred partners with the same mental illness. Thus, people with schizophrenia or ADHD are seven times more likely to have affected partners with the same disorder. This is even more pronounced for people with autism who are 10 times more likely to have a spouse with the same disorder.[95] Environment Main article: Brain health and pollution The prevalence of mental illness is higher in more economically unequal countries. During the prenatal stage, factors like unwanted pregnancy, lack of adaptation to pregnancy or substance use during pregnancy increases the risk of developing a mental disorder.[89] Maternal stress and birth complications including prematurity and infections have also been implicated in increasing susceptibility for mental illness.[96] Infants neglected or not provided optimal nutrition have a higher risk of developing cognitive impairment.[89] Social influences have also been found to be important,[97] including abuse, neglect, bullying, social stress, traumatic events, and other negative or overwhelming life experiences. Aspects of the wider community have also been implicated,[98] including employment problems, socioeconomic inequality, lack of social cohesion, problems linked to migration, and features of particular societies and cultures. The specific risks and pathways to particular disorders are less clear, however. Nutrition also plays a role in mental disorders.[10][99] In schizophrenia and psychosis, risk factors include migration and discrimination, childhood trauma, bereavement or separation in families, recreational use of drugs,[100] and urbanicity.[98] In anxiety, risk factors may include parenting factors including parental rejection, lack of parental warmth, high hostility, harsh discipline, high maternal negative affect, anxious childrearing, modelling of dysfunctional and drug-abusing behavior, and child abuse (emotional, physical and sexual).[101] Adults with imbalance work to life are at higher risk for developing anxiety.[89] For bipolar disorder, stress (such as childhood adversity) is not a specific cause, but does place genetically and biologically vulnerable individuals at risk for a more severe course of illness.[102] Drug use Mental disorders are associated with drug use including: cannabis,[103] alcohol[104] and caffeine,[105] use of which appears to promote anxiety.[106] For psychosis and schizophrenia, usage of a number of drugs has been associated with development of the disorder, including cannabis, cocaine, and amphetamines.[107][103] There has been debate regarding the relationship between usage of cannabis and bipolar disorder.[108] Cannabis has also been associated with depression.[103] Adolescents are at increased risk for tobacco, alcohol and drug use; Peer pressure is the main reason why adolescents start using substances. At this age, the use of substances could be detrimental to the development of the brain and place them at higher risk of developing a mental disorder.[89] Chronic disease People living with chronic conditions like HIV and diabetes are at higher risk of developing a mental disorder. People living with diabetes experience significant stress from the biological impact of the disease, which places them at risk for developing anxiety and depression. Diabetic patients also have to deal with emotional stress trying to manage the disease. Conditions like heart disease, stroke, respiratory conditions, cancer, and arthritis increase the risk of developing a mental disorder when compared to the general population.[109] Personality traits Risk factors for mental illness include a propensity for high neuroticism[110][111] or "emotional instability". In anxiety, risk factors may include temperament and attitudes (e.g. pessimism).[92] Causal models Mental disorders can arise from multiple sources, and in many cases there is no single accepted or consistent cause currently established. An eclectic or pluralistic mix of models may be used to explain particular disorders.[111][112] The primary paradigm of contemporary mainstream Western psychiatry is said to be the biopsychosocial model, which incorporates biological, psychological and social factors, although this may not always be applied in practice. Biological psychiatry follows a biomedical model where many mental disorders are conceptualized as disorders of brain circuits likely caused by developmental processes shaped by a complex interplay of genetics and experience. A common assumption is that disorders may have resulted from genetic and developmental vulnerabilities, exposed by stress in life (for example in a diathesis–stress model), although there are various views on what causes differences between individuals. Some types of mental disorders may be viewed as primarily neurodevelopmental disorders.[citation needed] A distinction is sometimes made between a "medical model" or a "social model" of psychiatric disability.[113] Diagnosis Psychiatrists seek to provide a medical diagnosis of individuals by an assessment of symptoms, signs and impairment associated with particular types of mental disorder. Other mental health professionals, such as clinical psychologists, may or may not apply the same diagnostic categories to their clinical formulation of a client's difficulties and circumstances.[114] The majority of mental health problems are, at least initially, assessed and treated by family physicians (in the UK general practitioners) during consultations, who may refer a patient on for more specialist diagnosis in acute or chronic cases. Routine diagnostic practice in mental health services typically involves an interview known as a mental status examination, where evaluations are made of appearance and behavior, self-reported symptoms, mental health history, and current life circumstances. The views of other professionals, relatives, or other third parties may be taken into account. A physical examination to check for ill health or the effects of medications or other drugs may be conducted. Psychological testing is sometimes used via paper-and-pen or computerized questionnaires, which may include algorithms based on ticking off standardized diagnostic criteria, and in rare specialist cases neuroimaging tests may be requested, but such methods are more commonly found in research studies than routine clinical practice.[115][116] Time and budgetary constraints often limit practicing psychiatrists from conducting more thorough diagnostic evaluations.[117] It has been found that most clinicians evaluate patients using an unstructured, open-ended approach, with limited training in evidence-based assessment methods, and that inaccurate diagnosis may be common in routine practice.[118] In addition, comorbidity is very common in psychiatric diagnosis, where the same person meets the criteria for more than one disorder. On the other hand, a person may have several different difficulties only some of which meet the criteria for being diagnosed. There may be specific problems with accurate diagnosis in developing countries. More structured approaches are being increasingly used to measure levels of mental illness. HoNOS is the most widely used measure in English mental health services, being used by at least 61 trusts.[119] In HoNOS a score of 0–4 is given for each of 12 factors, based on functional living capacity.[120] Research has been supportive of HoNOS,[121] although some questions have been asked about whether it provides adequate coverage of the range and complexity of mental illness problems, and whether the fact that often only 3 of the 12 scales vary over time gives enough subtlety to accurately measure outcomes of treatment.[122] Criticism icon This section relies excessively on references to primary sources. Please improve this section by adding secondary or tertiary sources. Find sources: "criticism" psychiatric diagnosis – news · newspapers · books · scholar · JSTOR (July 2021) (Learn how and when to remove this message) Since the 1980s, Paula Caplan has been concerned about the subjectivity of psychiatric diagnosis, and people being arbitrarily "slapped with a psychiatric label." Caplan says because psychiatric diagnosis is unregulated, doctors are not required to spend much time interviewing patients or to seek a second opinion. The Diagnostic and Statistical Manual of Mental Disorders can lead a psychiatrist to focus on narrow checklists of symptoms, with little consideration of what is actually causing the person's problems. So, according to Caplan, getting a psychiatric diagnosis and label often stands in the way of recovery.[123] In 2013, psychiatrist Allen Frances wrote a paper entitled "The New Crisis of Confidence in Psychiatric Diagnosis", which said that "psychiatric diagnosis... still relies exclusively on fallible subjective judgments rather than objective biological tests." Frances was also concerned about "unpredictable overdiagnosis."[124] For many years, marginalized psychiatrists (such as Peter Breggin, Thomas Szasz) and outside critics (such as Stuart A. Kirk) have "been accusing psychiatry of engaging in the systematic medicalization of normality." More recently these concerns have come from insiders who have worked for and promoted the American Psychiatric Association (e.g., Robert Spitzer, Allen Frances).[125] A 2002 editorial in the British Medical Journal warned of inappropriate medicalization leading to disease mongering, where the boundaries of the definition of illnesses are expanded to include personal problems as medical problems or risks of diseases are emphasized to broaden the market for medications.[126] Gary Greenberg, a psychoanalyst, in his book "the Book of Woe", argues that mental illness is really about suffering and how the DSM creates diagnostic labels to categorize people's suffering.[127] Indeed, the psychiatrist Thomas Szasz, in his book "the Medicalization of Everyday Life", also argues that what is psychiatric illness, is not always biological in nature (i.e. social problems, poverty, etc.), and may even be a part of the human condition.[128] Potential routine use of MRI/fMRI in diagnosis in 2018 the American Psychological Association commissioned a review to reach a consensus on whether modern clinical MRI/fMRI will be able to be used in the diagnosis of mental health disorders. The criteria presented by the APA stated that the biomarkers used in diagnosis should:

4월 06, 2026

Particle physics or high-energy physics is the study of fundamental particles and forces that constitute matter and radiation. The field also studies combinations of elementary particles up to the scale of protons and neutrons, while the study of combinations of protons and neutrons is called nuclear physics.

The fundamental particles in the universe are classified in the Standard Model as fermions (matter particles) and bosons (force-carrying particles). There are three generations of fermions, although ordinary matter is made only from the first fermion generation. The first generation consists of up and down quarks which form protons and neutrons, and electrons and electron neutrinos. The three fundamental interactions known to be mediated by bosons are electromagnetism, the weak interaction, and the strong interaction.

Quarks form hadrons, but cannot exist on their own. Hadrons that contain an odd number of quarks are called baryons and those that contain an even number are called mesons. Two baryons, the proton and the neutron, make up most of the mass of ordinary matter. Mesons are unstable and the longest-lived last for only a few hundredths of a microsecond. They occur after collisions between particles made of quarks, such as fast-moving protons and neutrons in cosmic rays. Mesons are also produced in cyclotrons or other particle accelerators.

Particles have corresponding antiparticles with the same mass but with opposite electric charges. For example, the antiparticle of the electron is the positron. The electron has a negative electric charge, the positron has a positive charge. These antiparticles can theoretically form a corresponding form of matter called antimatter. Some particles, such as the photon, are their own antiparticle.

These elementary particles are excitations of the quantum fields that also govern their interactions. The dominant theory explaining these fundamental particles and fields, along with their dynamics, is called the Standard Model. The reconciliation of gravity to the current particle physics theory is not solved; many theories have addressed this problem, such as loop quantum gravity, string theory and supersymmetry theory.

Experimental particle physics is the study of these particles in radioactive processes and in particle accelerators such as the Large Hadron Collider. Theoretical particle physics is the study of these particles in the context of cosmology and quantum theory. The two are closely interrelated: the Higgs boson was postulated theoretically before being confirmed by experiments.

History

The idea that all matter is fundamentally composed of elementary particles dates from at least the 6th century BC.^[1] In the 19th century, John Dalton, through his work on stoichiometry, concluded that each element of nature was composed of a single, unique type of particle.^[2] The word atom, after the Greek word atomos meaning "indivisible", has since then denoted the smallest particle of a chemical element, but physicists later discovered that atoms are not, in fact, the fundamental particles of nature, but are conglomerates of even smaller particles, such as the electron. The early 20th century explorations of nuclear physics and quantum physics led to proofs of nuclear fission in 1939 by Lise Meitner (based on experiments by Otto Hahn), and nuclear fusion by Hans Bethe in that same year; both discoveries also led to the development of nuclear weapons. Bethe's 1947 calculation of the Lamb shift is credited with having "opened the way to the modern era of particle physics".^[3]

Throughout the 1950s and 1960s, a bewildering variety of particles was found in collisions of particles from beams of increasingly high energy. It was referred to informally as the "particle zoo". Important discoveries such as the CP violation by James Cronin and Val Fitch brought new questions to matter-antimatter imbalance.^[4] After the formulation of the Standard Model during the 1970s, physicists clarified the origin of the particle zoo. The large number of particles was explained as combinations of a (relatively) small number of more fundamental particles and framed in the context of quantum field theories. This reclassification marked the beginning of modern particle physics.^[5]^[6]

Standard Model

The current state of the classification of all elementary particles is explained by the Standard Model, which gained widespread acceptance in the mid-1970s after experimental confirmation of the existence of quarks. It describes the strong, weak, and electromagnetic fundamental interactions, using mediating gauge bosons. The species of gauge bosons are eight gluons, W−
, W+
and Z bosons, and the photon.^[7] The Standard Model also contains 24 fundamental fermions (12 particles and their associated anti-particles), which are the constituents of all matter.^[8] Finally, the Standard Model also predicted the existence of a type of boson known as the Higgs boson. On 4 July 2012, physicists with the Large Hadron Collider at CERN announced they had found a new particle that behaves similarly to what is expected from the Higgs boson.^[9]

The Standard Model, as currently formulated, has 61 elementary particles.^[10] Those elementary particles can combine to form composite particles, accounting for the hundreds of other species of particles that have been discovered since the 1960s. The Standard Model has been found to agree with almost all the experimental tests conducted to date. However, most particle physicists believe that it is an incomplete description of nature and that a more fundamental theory awaits discovery (See Theory of Everything). In recent years, measurements of neutrino mass have provided the first experimental deviations from the Standard Model, since neutrinos do not have mass in the Standard Model.^[11]

Subatomic particles

Modern particle physics research is focused on subatomic particles, including atomic constituents, such as electrons, protons, and neutrons (protons and neutrons are composite particles called baryons, made of quarks), that are produced by radioactive and scattering processes; such particles are photons, neutrinos, and muons, as well as a wide range of exotic particles.^[12] All particles and their interactions observed to date can be described almost entirely by the Standard Model.^[7]

Elementary Particles
	Types	Generations	Antiparticle	Colours	Total
Quarks	2	3	Pair	3	36
Leptons	2	3	Pair	None	12
Gluons	1	None	Own	8	8
Photon			Own	None	1
Z Boson			Own		1
W Boson			Pair		2
Higgs			Own		1
Total number of (known) elementary particles:					61

Dynamics of particles are also governed by quantum mechanics; they exhibit wave–particle duality, displaying particle-like behaviour under certain experimental conditions and wave-like behaviour in others. In more technical terms, they are described by quantum state vectors in a Hilbert space, which is also treated in quantum field theory. Following the convention of particle physicists, the term elementary particles is applied to those particles that are, according to current understanding, presumed to be indivisible and not composed of other particles.^[10]

Quarks and leptons

Ordinary matter is made from first-generation quarks (up, down) and leptons (electron, electron neutrino).^[13] Collectively, quarks and leptons are called fermions. They have a quantum spin of half-integers (−1/2, 1/2, 3/2, etc.) and obey the Pauli exclusion principle, where no two particles may occupy the same quantum state.^[14] Quarks have fractional elementary electric charge (−1/3 or 2/3)^[15] and leptons have whole-numbered electric charge (0 or -1).^[16] Quarks also have color charge, which is labeled arbitrarily with no correlation to actual light color as red, green and blue.^[17] Because the interactions between the quarks store energy which can convert to other particles when the quarks are far apart enough, quarks cannot be observed independently. This is called color confinement.^[17]

There are three known generations of quarks (up and down, strange and charm, top and bottom) and leptons (electron and its neutrino, muon and its neutrino, tau and its neutrino), with strong indirect evidence that a fourth generation of fermions does not exist.^[18]

Bosons

Bosons are the mediators or carriers of fundamental interactions, such as electromagnetism, the weak interaction, and the strong interaction.^[19] Electromagnetism is mediated by the photon, the quanta of light.^[20]^: 29–30 The weak interaction is mediated by the W and Z bosons.^[21] The strong interaction is mediated by the gluon, which can link quarks together to form composite particles.^[22] Due to the aforementioned color confinement, gluons are never observed independently.^[23] The Higgs boson gives mass to the W and Z bosons via the Higgs mechanism^[24] – the gluon and photon are expected to be massless.^[23] All bosons have an integer quantum spin (0 and 1) and can have the same quantum state.^[19]

Antiparticles and color charge

Most aforementioned particles have corresponding antiparticles, which compose antimatter. Normal particles have positive lepton or baryon number, and antiparticles have these numbers negative.^[25] Most properties of corresponding antiparticles and particles are the same, with a few gets reversed; the electron's antiparticle, positron, has an opposite charge. To differentiate between antiparticles and particles, a plus or negative sign is added in superscript. For example, the electron and the positron are denoted e−
and e+
, respectively.^[26] However, in the case that the particle has a charge of 0 (equal to that of the antiparticle), the antiparticle is denoted with a line above the symbol. As such, an electron neutrino is $ν e$ , whereas its antineutrino is $ν e$ . When a particle and an antiparticle interact with each other, they are annihilated and convert to other particles.^[27] Some particles, such as the photon or gluon, have no antiparticles.^{[citation needed]}

Quarks and gluons additionally have color charges, which influences the strong interaction. Quark's color charges are called red, green and blue (though the particle itself have no physical color), and in antiquarks are called antired, antigreen and antiblue.^[17] The gluon can have eight color charges, which are the result of quarks' interactions to form composite particles (gauge symmetry SU(3)).^[28]

Composite

The neutrons and protons in the atomic nuclei are baryons – the neutron is composed of two down quarks and one up quark, and the proton is composed of two up quarks and one down quark.^[29] A baryon is composed of three quarks, and a meson is composed of two quarks (one normal, one anti). Baryons and mesons are collectively called hadrons. Quarks inside hadrons are governed by the strong interaction, thus are subjected to quantum chromodynamics (color charges). The bounded quarks must have their color charge to be neutral, or "white" for analogy with mixing the primary colors.^[30] More exotic hadrons can have other types, arrangement or number of quarks (tetraquark, pentaquark).^[31]

An atom is made from protons, neutrons and electrons.^[32] By modifying the particles inside a normal atom, exotic atoms can be formed.^[33] A simple example would be the hydrogen-4.1, which has one of its electrons replaced with a muon.^[34]

Hypothetical

The graviton is a hypothetical particle that can mediate the gravitational interaction, but it has not been detected or completely reconciled with current theories.^[35] Many other hypothetical particles have been proposed to address the limitations of the Standard Model. Notably, supersymmetric particles aim to solve the hierarchy problem, axions address the strong CP problem, and various other particles are proposed to explain the origins of dark matter and dark energy.

Experimental laboratories

The world's major particle physics laboratories are:

Brookhaven National Laboratory (Long Island, New York, United States). Its main facility is the Relativistic Heavy Ion Collider (RHIC), which collides heavy ions such as gold ions and polarized protons. It is the world's first heavy ion collider, and the world's only polarized proton collider.^[36]^[37]
Budker Institute of Nuclear Physics (Novosibirsk, Russia). Its main projects are now the electron-positron colliders VEPP-2000,^[38] operated since 2006, and VEPP-4,^[39] started experiments in 1994. Earlier facilities include the first electron–electron beam–beam collider VEP-1, which conducted experiments from 1964 to 1968; the electron-positron colliders VEPP-2, operated from 1965 to 1974; and, its successor VEPP-2M,^[40] performed experiments from 1974 to 2000.^[41]
CMS detector for LHC
CERN (European Organization for Nuclear Research) (Franco-Swiss border, near Geneva, Switzerland). Its main project is now the Large Hadron Collider (LHC), which had its first beam circulation on 10 September 2008, and is now the world's most energetic collider of protons. It also became the most energetic collider of heavy ions after it began colliding lead ions. Earlier facilities include the Large Electron–Positron Collider (LEP), which was stopped on 2 November 2000 and then dismantled to give way for LHC; and the Super Proton Synchrotron, which is being reused as a pre-accelerator for the LHC and for fixed-target experiments.^[42]
DESY (Deutsches Elektronen-Synchrotron) (Hamburg, Germany). Its main facility was the Hadron Elektron Ring Anlage (HERA), which collided electrons and positrons with protons.^[43] The accelerator complex is now focused on the production of synchrotron radiation with PETRA III, F

A mental disorder, also referred to as a mental illness,^[6] a mental health condition,^[7] or a psychiatric disability,^[2] is a behavioral or mental pattern that causes significant distress or impairment of personal functioning.^[8] A mental disorder is also characterized by a clinically significant disturbance in an individual's cognition, emotional regulation, or behavior, often in a social context.^[9]^[10] Such disturbances may occur as single episodes, may be persistent, or may be relapsing–remitting. There are many different types of mental disorders, with signs and symptoms that vary widely between specific disorders.^[10]^[11] A mental disorder is one aspect of mental health.

The causes of mental disorders are often unclear. Theories incorporate findings from a range of fields. Disorders may be associated with particular regions or functions of the brain. Disorders are usually diagnosed or assessed by a mental health professional, such as a clinical psychologist, psychiatrist, psychiatric nurse, or clinical social worker, using various methods such as psychometric tests, but often relying on observation and questioning. Cultural and religious beliefs, as well as social norms, should be taken into account when making a diagnosis.^[12]

Services for mental disorders are usually based in psychiatric hospitals, outpatient clinics, or in the community (in the United Kingdom). Treatments are provided by mental health professionals. Common treatment options are psychotherapy or psychiatric medication, while lifestyle changes, social interventions, peer support, and self-help are also options. In a minority of cases, there may be involuntary detention or treatment. Prevention programs have been shown to reduce depression.^[10]^[13]

In 2019, common mental disorders around the globe include: major depression, which affects about 264 million people; dementia, which affects about 50 million; bipolar disorder, which affects about 45 million; and schizophrenia and other psychoses, which affect about 20 million people.^[10] Neurodevelopmental disorders include attention deficit hyperactivity disorder (ADHD), autism spectrum disorder (autism), and intellectual disability, of which onset occurs early in the developmental period.^[14]^[10] Stigma and discrimination can add to the suffering and disability associated with mental disorders, leading to various social movements attempting to increase understanding and challenge social exclusion.

Definition

The definition and classification of mental disorders are key issues for researchers as well as service providers and those who may be diagnosed. For a mental state to be classified as a disorder, it generally needs to cause dysfunction.^[15] Most international clinical documents use the term mental "disorder", while "illness" is also common. It has been noted that using the term "mental" (i.e., of the mind) is not necessarily meant to imply separateness from the brain or body.

According to the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), published in 1994, a mental disorder is a psychological syndrome or pattern that is associated with distress (e.g., via a painful symptom), disability (impairment in one or more important areas of functioning), increased risk of death, or causes a significant loss of autonomy; however, it excludes normal responses such as the grief from loss of a loved one and also excludes deviant behavior for political, religious, or societal reasons not arising from a dysfunction in the individual.^[16]

The DSM-IV definition states that, like many medical terms, mental disorder "lacks a consistent operational definition that covers all situations". It notes that different levels of abstraction can be used for medical definitions, including pathology, symptomology, deviance from a normal range, or etiology, and that the same is true for mental disorders, so that sometimes one type of definition is appropriate and sometimes another, depending on the situation.^[17]

In 2013, the American Psychiatric Association (APA) redefined mental disorders in the DSM-5 as "a syndrome characterized by clinically significant disturbance in an individual's cognition, emotion regulation, or behavior that reflects a dysfunction in the psychological, biological, or developmental processes underlying mental functioning."^[18] The final draft of ICD-11 contains a very similar definition.^[19]

The terms "mental breakdown" or "nervous breakdown" may be used by the general population to mean a mental disorder.^[20] The terms "nervous breakdown" and "mental breakdown" have not been formally defined through a medical diagnostic system such as the DSM-5 or ICD-10 and are nearly absent from scientific literature regarding mental illness.^[21]^[22] Although "nervous breakdown" is not rigorously defined, surveys of laypersons suggest that the term refers to a specific acute time-limited reactive disorder involving symptoms such as anxiety or depression, usually precipitated by external stressors.^[21] Many health experts today refer to a nervous breakdown as a mental health crisis.^[23]

Nervous illness

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In addition to the concept of mental disorder, some people have argued for a return to the old-fashioned concept of nervous illness. In How Everyone Became Depressed: The Rise and Fall of the Nervous Breakdown (2013), Edward Shorter, a professor of psychiatry and the history of medicine, says:

We have had nervous illness for centuries. When you are too nervous to function ... it is a nervous breakdown. But that term has vanished from medicine, although not from the way we speak.... The nervous patients of yesteryear are the depressives of today. That is the bad news.... There is a deeper illness that drives depression and the symptoms of mood. We can call this deeper illness something else, or invent a neologism, but we need to get the discussion off depression and onto this deeper disorder in the brain and body. That is the point.

— Edward Shorter, the University of Toronto^[24]

In eliminating the nervous breakdown, psychiatry has come close to having its own nervous breakdown.

— David Healy, MD, FRCPsych, Professor of Psychiatry, University of Cardiff, Wales^[25]

Nerves stand at the core of common mental illness, no matter how much we try to forget them.

— Peter J. Tyrer, FMedSci, Professor of Community Psychiatry, Imperial College, London^[26]

Classifications

There are currently two widely established systems that classify mental disorders:

International Classification of Diseases produced by the WHO. The latest edition is the ICD-11, which is in effect since 1 January 2022.^[27] The ICD is a broad medical classification system; mental disorders are contained in Chapter 06: Mental, behavioural or neurodevelopmental disorders (06).
Diagnostic and Statistical Manual of Mental Disorders produced by the American Psychiatric Association since 1952. The latest edition is the Fifth Edition, Text Revision (DSM-5-TR), which was released in 2022.^[28]

Both of these list categories of disorder and provide standardized criteria for diagnosis. They have deliberately converged their codes in recent revisions so that the manuals are often broadly comparable, although significant differences remain. Other classification schemes may be used in non-western cultures, for example, the Chinese Classification of Mental Disorders, and other manuals may be used by those of alternative theoretical persuasions, such as the Psychodynamic Diagnostic Manual. In general, mental disorders are classified separately from neurological disorders, learning disabilities or intellectual disability.

Unlike the DSM and ICD, some approaches are not based on identifying distinct categories of disorder using dichotomous symptom profiles intended to separate the abnormal from the normal. There is significant scientific debate about the relative merits of categorical versus such non-categorical (or hybrid) schemes, also known as continuum or dimensional models. A spectrum approach may incorporate elements of both.

In the scientific and academic literature on the definition or classification of mental disorder, one extreme argues that it is entirely a matter of value judgements (including of what is normal) while another proposes that it is or could be entirely objective and scientific (including by reference to statistical norms).^[29] Common hybrid views argue that the concept of mental disorder is objective even if only a "fuzzy prototype" that can never be precisely defined, or conversely that the concept always involves a mixture of scientific facts and subjective value judgments.^[30] Although the diagnostic categories are referred to as 'disorders', they are presented as medical diseases, but are not validated in the same way as most medical diagnoses. Some neurologists argue that classification will only be reliable and valid when based on neurobiological features rather than clinical interview, while others suggest that the differing ideological and practical perspectives need to be better integrated.^[31]^[32]

The DSM and ICD approach remains under attack both because of the implied causality model^[33] and because some researchers believe it better to aim at underlying brain differences which can precede symptoms by many years.^[34]

Dimensional models

The high degree of comorbidity between disorders in categorical models such as the DSM and ICD have led some to propose dimensional models. Studying comorbidity between disorders have demonstrated two latent (unobserved) factors or dimensions in the structure of mental disorders that are thought to possibly reflect etiological processes. These two dimensions reflect a distinction between internalizing disorders, such as mood or anxiety symptoms, and externalizing disorders such as behavioral or substance use symptoms.^[35] A single general factor of psychopathology, similar to the g factor for intelligence, has been empirically supported. The p factor model supports the internalizing-externalizing distinction, but also supports the formation of a third dimension of thought disorders such as schizophrenia.^[36] Biological evidence also supports the validity of the internalizing-externalizing structure of mental disorders, with twin and adoption studies supporting heritable factors for externalizing and internalizing disorders.^[37]^[38]^[39] A leading dimensional model is the Hierarchical Taxonomy of Psychopathology.

Disorders

There are many different categories of mental disorder, and many different facets of human behavior and personality that can become disordered.^[40]^[41]^[42]^[43]

Anxiety disorders

An anxiety disorder is anxiety or fear that interferes with normal functioning.^[41] Commonly recognized categories include specific phobias, generalized anxiety disorder, social anxiety disorder, panic disorder, agoraphobia, and post-traumatic stress disorder. Obsessive–compulsive disorder was categorized as an anxiety disorder in DSM-III, which was published in 1980, but was later placed in its own section called "Obsessive-Compulsive and Related Disorder" in DSM-5.^[44]

Mood disorders

Other affective (emotion/mood) processes can also become disordered. Mood disorder involving unusually intense and sustained sadness, melancholia, or despair is known as major depression (also known as unipolar or clinical depression). Milder, but still prolonged depression, can be diagnosed as dysthymia. Bipolar disorder (also known as manic depression) involves abnormally "high" or pressured mood states, known as mania or hypomania, alternating with normal or depressed moods. The extent to which unipolar and bipolar mood phenomena represent distinct categories of disorder, or mix and merge along a dimension or spectrum of mood, is subject to some scientific debate.^[45]^[46]

Psychotic disorders

Patterns of belief, language use and perception of reality can become dysregulated (e.g., delusions, thought disorder, hallucinations). Psychotic disorders in this domain include schizophrenia, and delusional disorder. Schizoaffective disorder is a category used for individuals showing aspects of both schizophrenia and affective disorders. Schizotypy is a category used for individuals showing some of the characteristics associated with schizophrenia, but without meeting cutoff criteria.^{[citation needed]}

Personality disorders

Personality—the fundamental characteristics of a person that influence thoughts and behaviors across situations and time—may be considered disordered if judged to be abnormally rigid and maladaptive. Although treated separately by some^{[by whom?]}, the commonly used categorical schemes^[which?] include them as mental disorders. Personality disorders, in general, are defined as emerging in childhood, or at least by adolescence or early adulthood. There is an emerging consensus that personality disorders, similar to personality traits in general, incorporate a mixture of acute dysfunctional behaviors that may resolve in short periods, and maladaptive temperamental traits that are more enduring.^[47] Furthermore, there are also non-categorical schemes that rate all individuals via a profile of different dimensions of personality without a symptom-based cutoff from normal personality variation, for example through schemes based on dimensional models of personality disorders.^[48]^[49]^{[non-primary source needed]}

A number of different personality disorders are listed in the DSM-5-TR, including those sometimes classed as eccentric, such as paranoid, schizoid and schizotypal personality disorders; types that have described as dramatic or emotional, such as antisocial, borderline, histrionic or narcissistic personality disorders; and those sometimes classed as fear-related, such as anxious-avoidant, dependent, or obsessive–compulsive personality disorders.^{[citation needed]}

While the DSM-5-TR standard model diagnoses personality disorders as distinct categories, the ICD-11 classification of personality disorders contains a single, dimensional personality disorder which is diagnosed according to severity, with the possibility to additionally diagnose trait domains.^[50] In the case of the Alternative DSM-5 Model for Personality disorders, the approach chosen is a dimensional–categorical model,^[51] in which diagnosis can consist of either predefined categories based on specific combinations of traits and functioning levels,^[52] or of a general diagnosis called personality disorder – trait specified.^[52] The ICD-11 classifies schizotypal disorder among primary psychotic disorders rather than as a personality disorder as in the DSM-5.^[53]

Neurodevelopmental disorders

Neurodevelopmental disorders are a group of mental disorders that affect the central nervous system, such as the brain and spinal cord.^[54] These disorders can appear in early childhood.^[55] They can even persist into adulthood.^[56] A few of the common are attention deficit hyperactivity disorder (ADHD), autism spectrum disorder (autism), intellectual disabilities, motor disorders, and communication disorders among others. Some causes can contribute to these disorders, such as genetic factors (genetics, family medical history),^[57] environmental factors (excessive stress, exposure to neurotoxins, pollution, viral infections, bacterial infections),^[58]^[59] physical factors (traumatic brain injury, illness),^[60] and prenatal factors (birth defects, exposure to drugs during pregnancy, low birth weight).^[61] Neurodevelopmental disorders can be managed with behavioral therapy, applied behavior analysis (ABA), educational interventions, specific medications, and other such treatments.^[62]

Approximately 8 in 10 people with autism suffer from a mental health problem in their lifetime, in comparison to 1 in 4 of the general population that suffers from a mental health problem in their lifetimes.^[63]^[64]^[65]

Eating disorders

An eating disorder is a serious mental health condition that involves an unhealthy relationship with food and body image. They can cause severe physical and psychological problems.^[66] Eating disorders involve disproportionate concern in matters of food and weight.^[41] Categories eating disorders include anorexia nervosa, bulimia nervosa, exercise bulimia, or binge eating disorder.^[67]^[68]

Sleep disorders

Sleep disorders are associated with disruption to normal sleep patterns. A common sleep disorder is insomnia, which is described as difficulty falling and/or staying asleep. Other sleep disorders include narcolepsy, sleep apnea, REM sleep behavior disorder, chronic sleep deprivation, and restless leg syndrome.

Narcolepsy is a condition of extreme tendencies to fall asleep whenever and wherever. People with narcolepsy feel refreshed after their random sleep, but eventually get sleepy again. Narcolepsy diagnosis requires an overnight stay at a sleep center for analysis, during which doctors ask for a detailed sleep history and sleep records. Doctors also use actigraphs and polysomnography.^[69] Doctors will do a multiple sleep latency test, which measures how long it takes a person to fall asleep.^[69]

Sleep apnea, when breathing repeatedly stops and starts during sleep, can be a serious sleep disorder. Three types of sleep apnea include obstructive sleep apnea, central sleep apnea, and complex sleep apnea.^[70] Sleep apnea can be diagnosed at home or with polysomnography at a sleep center. An ear, nose, and throat doctor may further help with the sleeping habits.

Sexuality related

Sexual disorders include dyspareunia and various kinds of paraphilia (sexual arousal to objects, situations, or individuals that are considered abnormal or harmful to the person or others).^{[citation needed]}

Other

Impulse control disorders: People who are abnormally unable to resist certain urges or impulses that could be harmful to themselves or others, may be classified as having an impulse control disorder, and disorders such as kleptomania (stealing) or pyromania (fire-setting). Various behavioral addictions, such as gambling addiction, may be classed as a disorder.^{[citation needed]}

Substance use disorders: This disorder refers to the use of drugs (legal or illegal, including alcohol) that persists despite significant problems or harm related to its use. Substance dependence and substance abuse fall under this umbrella category in the DSM. Substance use disorder may be due to a pattern of compulsive and repetitive use of a drug that results in tolerance to its effects and withdrawal symptoms when use is reduced or stopped.^{[citation needed]}

Dissociative disorders: People with severe disturbances of their self-identity, memory, and general awareness of themselves and their surroundings may be classified as having these types of disorders, including depersonalization-derealization disorder or dissociative identity disorder (which was previously referred to as multiple personality disorder or "split personality").^{[citation needed]}

Cognitive disorders: These affect cognitive abilities, including learning and memory. This category includes delirium and mild and major neurocognitive disorder (previously termed dementia).^{[citation needed]}

Somatoform disorders may be diagnosed when there are problems that appear to originate in the body that are thought to be manifestations of a mental disorder. This includes somatization disorder and conversion disorder. There are also disorders of how a person perceives their body, such as body dysmorphic disorder. Neurasthenia is an old diagnosis involving somatic complaints as well as fatigue and low spirits/depression, which is officially recognized by the ICD-10 but no longer by the DSM-IV.^[71]^{[non-primary source needed]}

Factitious disorders are diagnosed where symptoms are thought to be reported for personal gain. Symptoms are often deliberately produced or feigned, and may relate to either symptoms in the individual or in someone close to them, particularly people they care for.^{[citation needed]}

There are attempts to introduce a category of relational disorder, where the diagnosis is of a relationship rather than on any one individual in that relationship. The relationship may be between children and their parents, between couples, or others. There already exists, under the category of psychosis, a diagnosis of shared psychotic disorder where two or more individuals share a particular delusion because of their close relationship with each other.^{[citation needed]}

There are a number of uncommon psychiatric syndromes, which are often named after the person who first described them, such as Capgras syndrome, De Clerambault syndrome, Othello syndrome, Ganser syndrome, Cotard delusion, and Ekbom syndrome, and additional disorders such as the Couvade syndrome and Geschwind syndrome.^[72]

Signs and symptoms

Course

The onset of psychiatric disorders usually occurs from childhood to early adulthood.^[73] Impulse-control disorders and a few anxiety disorders tend to appear in childhood. Some other anxiety disorders, substance disorders, and mood disorders emerge later in the mid-teens.^[74] Symptoms of schizophrenia typically manifest from late adolescence to early twenties.^[75]

The likely course and outcome of mental disorders vary and are dependent on numerous factors related to the disorder itself, the individual as a whole, and the social environment. Some disorders may last a brief period of time, while others may be long-term in nature.

All disorders can have a varied course. Long-term international studies of schizophrenia have found that over a half of individuals recover in terms of symptoms, and around a fifth to a third in terms of symptoms and functioning, with many requiring no medication. While some have serious difficulties and support needs for many years, "late" recovery is still plausible. The World Health Organization (WHO) concluded that the long-term studies' findings converged with others in "relieving patients, carers and clinicians of the chronicity paradigm which dominated thinking throughout much of the 20th century."^[76]^{[non-primary source needed]}^[77]

A follow-up study by Tohen and coworkers revealed that around half of people initially diagnosed with bipolar disorder achieve symptomatic recovery (no longer meeting criteria for the diagnosis) within six weeks, and nearly all achieve it within two years, with nearly half regaining their prior occupational and residential status in that period. Less than half go on to experience a new episode of mania or major depression within the next two years.^[78]^{[non-primary source needed]}

Disability

Disorder	Disability-adjusted life years^[79]
Major depressive disorder	65.5 million
Alcohol-use disorder	23.7 million
Schizophrenia	16.8 million
Bipolar disorder	14.4 million
Other drug-use disorders	8.4 million
Panic disorder	7.0 million
Obsessive-compulsive disorder	5.1 million
Primary insomnia	3.6 million
Post-traumatic stress disorder	3.5 million

Some disorders may be very limited in their functional effects, while others may involve substantial disability and support needs. In this context, the terms psychiatric disability and psychological disability are sometimes used instead of mental disorder.^[2]^[3] The degree of ability or disability may vary over time and across different life domains. Furthermore, psychiatric disability has been linked to institutionalization, discrimination and social exclusion as well as to the inherent effects of disorders. Alternatively, functioning may be affected by the stress of having to hide a condition in work or school, etc., by adverse effects of medications or other substances, or by mismatches between illness-related variations and demands for regularity.^[80]

It is also the case that, while often being characterized in purely negative terms, some mental traits or states labeled as psychiatric disabilities can also involve above-average creativity, non-conformity, goal-striving, meticulousness, or empathy.^[81] In addition, the public perception of the level of disability associated with mental disorders can change.^[82]

Nevertheless, internationally, people report equal or greater disability from commonly occurring mental conditions than from commonly occurring physical conditions, particularly in their social roles and personal relationships. The proportion with access to professional help for mental disorders is far lower, however, even among those assessed as having a severe psychiatric disability.^[83] Disability in this context may or may not involve such things as:

Basic activities of daily living. Including looking after the self (health care, grooming, dressing, shopping, cooking etc.) or looking after accommodation (chores, DIY tasks, etc.)
Interpersonal relationships. Including communication skills, ability to form relationships and sustain them, ability to leave the home or mix in crowds or particular settings
Occupational functioning. Ability to acquire an employment and hold it, cognitive and social skills required for the job, dealing with workplace culture, or studying as a student.

In terms of total disability-adjusted life years (DALYs), which is an estimate of how many years of life are lost due to premature death or to being in a state of poor health and disability, psychiatric disabilities rank amongst the most disabling conditions. Unipolar depressive disorder (also known as major depressive disorder) is the third leading cause of disability worldwide, of any condition mental or physical, accounting for 65.5 million years lost. The first systematic description of global disability arising in youth, in 2011, found that among 10- to 24-year-olds nearly half of all disability (current and as estimated to continue) was due to psychiatric disabilities, including substance use disorders and conditions involving self-harm. Second to this were accidental injuries (mainly traffic collisions) accounting for 12 percent of disability, followed by communicable diseases at 10 percent. The psychiatric disabilities associated with most disabilities in high-income countries were unipolar major depression (20%) and alcohol use disorder (11%). In the eastern Mediterranean region, it was unipolar major depression (12%) and schizophrenia (7%), and in Africa it was unipolar major depression (7%) and bipolar disorder (5%).^[84]

Suicide, which is often attributed to some underlying mental disorder, is a leading cause of death among teenagers and adults under 35.^[85]^[86] There are an estimated 10 to 20 million non-fatal attempted suicides every year worldwide.^[87]

Risk factors

The predominant view as of 2018 is that genetic, psychological, and environmental factors all contribute to the development or progression of mental disorders.^[88] Different risk factors may be present at different ages, with risk occurring as early as during prenatal period.^[89]

Genetics

A number of psychiatric disorders are linked to a family history (including depression, narcissistic personality disorder^[90]^[91] and anxiety).^[92] Twin studies have also revealed a very high heritability for many mental disorders (especially autism and schizophrenia).^[93] Although researchers have been looking for decades for clear linkages between genetics and mental disorders, that work has not yielded specific genetic biomarkers yet that might lead to better diagnosis and better treatments.^[94]

Statistical research looking at eleven disorders found widespread assortative mating between people with mental illness. That means that individuals with one of these disorders were two to three times more likely than the general population to have a partner with a mental disorder. Sometimes people seemed to have preferred partners with the same mental illness. Thus, people with schizophrenia or ADHD are seven times more likely to have affected partners with the same disorder. This is even more pronounced for people with autism who are 10 times more likely to have a spouse with the same disorder.^[95]

Environment

During the prenatal stage, factors like unwanted pregnancy, lack of adaptation to pregnancy or substance use during pregnancy increases the risk of developing a mental disorder.^[89] Maternal stress and birth complications including prematurity and infections have also been implicated in increasing susceptibility for mental illness.^[96] Infants neglected or not provided optimal nutrition have a higher risk of developing cognitive impairment.^[89]

Social influences have also been found to be important,^[97] including abuse, neglect, bullying, social stress, traumatic events, and other negative or overwhelming life experiences. Aspects of the wider community have also been implicated,^[98] including employment problems, socioeconomic inequality, lack of social cohesion, problems linked to migration, and features of particular societies and cultures. The specific risks and pathways to particular disorders are less clear, however.

Nutrition also plays a role in mental disorders.^[10]^[99]

In schizophrenia and psychosis, risk factors include migration and discrimination, childhood trauma, bereavement or separation in families, recreational use of drugs,^[100] and urbanicity.^[98]

In anxiety, risk factors may include parenting factors including parental rejection, lack of parental warmth, high hostility, harsh discipline, high maternal negative affect, anxious childrearing, modelling of dysfunctional and drug-abusing behavior, and child abuse (emotional, physical and sexual).^[101] Adults with imbalance work to life are at higher risk for developing anxiety.^[89]

For bipolar disorder, stress (such as childhood adversity) is not a specific cause, but does place genetically and biologically vulnerable individuals at risk for a more severe course of illness.^[102]

Drug use

Mental disorders are associated with drug use including: cannabis,^[103] alcohol^[104] and caffeine,^[105] use of which appears to promote anxiety.^[106] For psychosis and schizophrenia, usage of a number of drugs has been associated with development of the disorder, including cannabis, cocaine, and amphetamines.^[107]^[103] There has been debate regarding the relationship between usage of cannabis and bipolar disorder.^[108] Cannabis has also been associated with depression.^[103] Adolescents are at increased risk for tobacco, alcohol and drug use; Peer pressure is the main reason why adolescents start using substances. At this age, the use of substances could be detrimental to the development of the brain and place them at higher risk of developing a mental disorder.^[89]

Chronic disease

People living with chronic conditions like HIV and diabetes are at higher risk of developing a mental disorder. People living with diabetes experience significant stress from the biological impact of the disease, which places them at risk for developing anxiety and depression. Diabetic patients also have to deal with emotional stress trying to manage the disease. Conditions like heart disease, stroke, respiratory conditions, cancer, and arthritis increase the risk of developing a mental disorder when compared to the general population.^[109]

Personality traits

Risk factors for mental illness include a propensity for high neuroticism^[110]^[111] or "emotional instability". In anxiety, risk factors may include temperament and attitudes (e.g. pessimism).^[92]

Causal models

Mental disorders can arise from multiple sources, and in many cases there is no single accepted or consistent cause currently established. An eclectic or pluralistic mix of models may be used to explain particular disorders.^[111]^[112] The primary paradigm of contemporary mainstream Western psychiatry is said to be the biopsychosocial model, which incorporates biological, psychological and social factors, although this may not always be applied in practice.

Biological psychiatry follows a biomedical model where many mental disorders are conceptualized as disorders of brain circuits likely caused by developmental processes shaped by a complex interplay of genetics and experience. A common assumption is that disorders may have resulted from genetic and developmental vulnerabilities, exposed by stress in life (for example in a diathesis–stress model), although there are various views on what causes differences between individuals. Some types of mental disorders may be viewed as primarily neurodevelopmental disorders.^{[citation needed]}

A distinction is sometimes made between a "medical model" or a "social model" of psychiatric disability.^[113]

Diagnosis

Psychiatrists seek to provide a medical diagnosis of individuals by an assessment of symptoms, signs and impairment associated with particular types of mental disorder. Other mental health professionals, such as clinical psychologists, may or may not apply the same diagnostic categories to their clinical formulation of a client's difficulties and circumstances.^[114] The majority of mental health problems are, at least initially, assessed and treated by family physicians (in the UK general practitioners) during consultations, who may refer a patient on for more specialist diagnosis in acute or chronic cases.

Routine diagnostic practice in mental health services typically involves an interview known as a mental status examination, where evaluations are made of appearance and behavior, self-reported symptoms, mental health history, and current life circumstances. The views of other professionals, relatives, or other third parties may be taken into account. A physical examination to check for ill health or the effects of medications or other drugs may be conducted. Psychological testing is sometimes used via paper-and-pen or computerized questionnaires, which may include algorithms based on ticking off standardized diagnostic criteria, and in rare specialist cases neuroimaging tests may be requested, but such methods are more commonly found in research studies than routine clinical practice.^[115]^[116]

Time and budgetary constraints often limit practicing psychiatrists from conducting more thorough diagnostic evaluations.^[117] It has been found that most clinicians evaluate patients using an unstructured, open-ended approach, with limited training in evidence-based assessment methods, and that inaccurate diagnosis may be common in routine practice.^[118] In addition, comorbidity is very common in psychiatric diagnosis, where the same person meets the criteria for more than one disorder. On the other hand, a person may have several different difficulties only some of which meet the criteria for being diagnosed. There may be specific problems with accurate diagnosis in developing countries.

More structured approaches are being increasingly used to measure levels of mental illness.

HoNOS is the most widely used measure in English mental health services, being used by at least 61 trusts.^[119] In HoNOS a score of 0–4 is given for each of 12 factors, based on functional living capacity.^[120] Research has been supportive of HoNOS,^[121] although some questions have been asked about whether it provides adequate coverage of the range and complexity of mental illness problems, and whether the fact that often only 3 of the 12 scales vary over time gives enough subtlety to accurately measure outcomes of treatment.^[122]

Criticism

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Since the 1980s, Paula Caplan has been concerned about the subjectivity of psychiatric diagnosis, and people being arbitrarily "slapped with a psychiatric label." Caplan says because psychiatric diagnosis is unregulated, doctors are not required to spend much time interviewing patients or to seek a second opinion. The Diagnostic and Statistical Manual of Mental Disorders can lead a psychiatrist to focus on narrow checklists of symptoms, with little consideration of what is actually causing the person's problems. So, according to Caplan, getting a psychiatric diagnosis and label often stands in the way of recovery.^[123]

In 2013, psychiatrist Allen Frances wrote a paper entitled "The New Crisis of Confidence in Psychiatric Diagnosis", which said that "psychiatric diagnosis... still relies exclusively on fallible subjective judgments rather than objective biological tests." Frances was also concerned about "unpredictable overdiagnosis."^[124] For many years, marginalized psychiatrists (such as Peter Breggin, Thomas Szasz) and outside critics (such as Stuart A. Kirk) have "been accusing psychiatry of engaging in the systematic medicalization of normality." More recently these concerns have come from insiders who have worked for and promoted the American Psychiatric Association (e.g., Robert Spitzer, Allen Frances).^[125] A 2002 editorial in the British Medical Journal warned of inappropriate medicalization leading to disease mongering, where the boundaries of the definition of illnesses are expanded to include personal problems as medical problems or risks of diseases are emphasized to broaden the market for medications.^[126]

Gary Greenberg, a psychoanalyst, in his book "the Book of Woe", argues that mental illness is really about suffering and how the DSM creates diagnostic labels to categorize people's suffering.^[127] Indeed, the psychiatrist Thomas Szasz, in his book "the Medicalization of Everyday Life", also argues that what is psychiatric illness, is not always biological in nature (i.e. social problems, poverty, etc.), and may even be a part of the human condition.^[128]

Potential routine use of MRI/fMRI in diagnosis

in 2018 the American Psychological Association commissioned a review to reach a consensus on whether modern clinical MRI/fMRI will be able to be used in the diagnosis of mental health disorders. The criteria presented by the APA stated that the biomarkers used in diagnosis should: