Psychology

A number of mental disturbances, such as melancholy, hysteria and phobia, were described long ago in Ancient Greece and Rome, while others such as schizophrenia may not have been recognized.[1] Hippocrates considered the idea that mental illness may be related to biology.[2]
Psychiatric theories and treatments for mental illness developed in Islamic medicine in the Middle East, notably from the 8th century at the Baghdad Hospital under the physician Rhazes.
Medieval Europe had focused on demonic possession as the explanation of aberrant behavior.[3] Paracelsus used the word lunatic to describe behavior thought to be caused by the lunar effect.[4] Many other terms for mental disorder that found their way into everyday use have been traced to initial use in the 16th and 17th centuries. [5] Shakespeare and his contemporaries frequently depicted mental disorders in their plays. [6] Conditions of "shell shock" came to be recognized in war veterans. Homosexuality was viewed as a mental illness. From the early study of mental illness through individuals such as Philippe Pinel, Sigmund Freud, and Alois Alzheimer, much has changed in the development and understanding of mental illness and continues to change today.
At the start of the 20th century there were only a dozen officially recognized mental health conditions.[citation needed]. By 1952 there were 192 and the Diagnostic and Statistical Manual of Mental Disorder, Fourth Edition (DSM-IV) today lists 374.

There are many different categories of mental disorder, and many different facets of human behavior and personality that can become disordered.[7][8][9][10]
The state of anxiety or fear can become disordered, so that it is unusually intense or generalized over a prolonged period of time. Commonly recognized categories of anxiety disorders include specific phobia, Generalized anxiety disorder, Social Anxiety Disorder, Panic Disorder, Agoraphobia, Obsessive-Compulsive Disorder, Post-traumatic stress disorder. Relatively long lasting affective states can also become disordered. Mood disorder involving unusually intense and sustained sadness, melancholia or despair is know as Clinical depression (or Major depression), and may more generally be described as Emotional dysregulation. Milder but prolonged depression can be diagnosed as dysthymia. Bipolar disorder involves abnormally "high" or pressured mood states, known as mania or hypomania, alternating with normal or depressed mood. Whether unipolar and bipolar mood phenomena represent distinct categories of disorder, or whether they usually mix and merge together along a dimension or spectrum of mood, is under debate in the scientific literature.[11]
Patterns of belief, language use and perception can become disordered. Psychotic disorders centrally involving 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 traits associated with schizophrenia but without meeting cut-off criteria.
The fundamental characteristics of a person that influence his or her cognitions, motivations, and behaviors across situations and time - can be seen as disordered due to being abnormally rigid and maladaptive. Categorical schemes list a number of different personality disorders, such as those classed as eccentric (e.g. Paranoid personality disorder, Schizoid personality disorder, Schizotypal personality disorder), those described as dramatic or emotional (Antisocial personality disorder, Borderline personality disorder, Histrionic personality disorder, Narcissistic personality disorder) or those seen as fear-related (Avoidant personality disorder, Dependent personality disorder, Obsessive-compulsive personality disorder).
There may be an emerging consensus that personality disorders, like personality traits in the normal range, incorporate a mixture of more acute dysfunctional behaviors that resolve in relatively short periods, and maladaptive temperamental traits that are relatively more stable.[12] Non-categorical schemes may rate individuals via a profile across different dimensions of personality that are not seen as cut off from normal personality variation, commonly through schemes based on the Big Five personality traits.[13]
Other disorders may involve other attributes of human functioning. Eating practices can be disordered, at least in relatively rich industrialized areas, with either compulsive over-eating or under-eating or binging. Categories of disorder in this area include Anorexia nervosa and Bulimia nervosa or Binge eating disorder. Sleep disorders such as Insomnia also exist and can disrupt normal sleep patterns. Sexual and gender identity disorders, such as Dyspareunia or Gender identity disorder or ego-dystonic homosexuality. People who are abnormally unable to resist urges, or impulses, to perform acts that could be harmful to themselves or others, may be classed as having an impulse control disorder, including various kinds of Tic disorders such as Tourette's Syndrome, and disorders such as Kleptomania (stealing) or Pyromania (fire-setting). Substance-use disorders include Substance abuse disorder. Addictive gambling may be classed as a disorder. Inability to sufficiently adjust to life circumstances may be classed as an Adjustment disorder. The category of adjustment disorder is usually reserved for problems beginning within three months of the event or situation and ending within six months after the stressor stops or is eliminated. People who suffer severe disturbances of their self-identity, memory and general awareness of themselves and their surroundings may be classed as having a Dissociative identity disorder, such as Depersonalization disorder or Dissociative Identify Disorder itself (which has also been called multiple personality disorder, or "split personality".). Factitious disorders, such as Munchausen syndrome, also exist where symptoms are experienced and/or reported for personal gain.
Disorders appearing to originate in the body, but thought to be mental, are known as somatoform disorders, including Somatization disorder. There are also disorders of the perception of the body, including Body dysmorphic disorder. Neurasthenia is a category involving somatic complaints as well as fatigue and low spirits/depression, which is officially recognized by the ICD-10 but not by the DSM-IV.[14] Memory or cognitive disorders, such as amnesia or Alzheimer's disease exist.
Some disorders are thought to usually first occur in the context of early childhood development, although they may continue into adulthood. The category of Specific developmental disorder may be used to refer to circumscribed patterns of disorder in particular learning skills, motor skills, or communication skills. Disorder which appears more generalized may be classed as pervasive developmental disorders (PDD) also known as autism spectrum disorders (ASD); these include autism, Asperger's, Rett syndrome, childhood disintegrative disorder and other types of PDD whose exact diagnosis may not be specified. Other disorders mainly or first occurring in childhood include Reactive attachment disorder; Separation Anxiety Disorder; Oppositional Defiant Disorder; Attention Deficit Hyperactivity Disorder.