In psychiatry, derailment (also loosening of association, asyndesis, asyndetic thinking, knight's move thinking, or entgleisen) is a thought disorder characterized by discourse consisting of a sequence of unrelated or only remotely related ideas. The frame of reference often changes from one sentence to the next.

In a mild manifestation, this thought disorder is characterized by slippage of ideas further and further from the point of a discussion. Derailment can often be manifestly caused by intense emotions such as euphoria or hysteria. Some of the synonyms given above ("loosening of association", "asyndetic thinking") are used by some authors to refer just to a "loss of goal": discourse that sets off on a particular idea, wanders off and never returns to it. A related term is tangentiality—it refers to off-the-point, oblique or irrelevant answers given to questions. In some studies on creativity, "knight's move thinking", while it describes a similarly loose association of ideas, is not considered a mental disorder or the hallmark of one; it is sometimes used as a synonym for lateral thinking.

Thought disorder (TD) or formal thought disorder (FTD) refers to disorganized thinking as evidenced by disorganized speech. Specific thought disorders include derailment, poverty of speech, tangentiality, illogicality, perseveration, and thought blocking.

Psychiatrists consider formal thought disorder as being one of two types of disordered thinking, with the other type being delusions. The latter involves "content" while the former involves "form". Although the term "thought disorder" can refer to either type, in common parlance it refers most often to a disorder of thought "form" also known as formal thought disorder.

Eugen Bleuler, who named schizophrenia, held that thought disorder was its defining characteristic. However, formal thought disorder is not unique to schizophrenia or psychosis. It is often a symptom of mania, and less often it can be present in other mental disorders such as depression. Clanging or echolalia may be present in Tourette syndrome. Patients with a clouded consciousness, like that found in delirium, also have a formal thought disorder.

However, there is a clinical difference between these two groups. Those with schizophrenia or psychosis are less likely to demonstrate awareness or concern about the disordered thinking. Clayton and Winokur have suggested that this results from a fundamental inability to use the same type of Aristotelian logic as others. On the other hand, patients with a clouded consciousness, referred to as "organic" patients, usually do demonstrate awareness and concern, and complain about being "confused" or "unable to think straight"; Clayton and Winokur suggest that this is because their thought disorder results, instead, from various cognitive deficits.

Treatment often involves the use of behavioral modification and anticonvulsants, antidepressants and anxiolytics.

Most of the treatments for thought insertion are not specific to the symptom, but rather the symptom is treated through treatment of the psychopathology that causes it. However, one case report considers a way to manage thought insertion through performing thoughts as motor actions of speech. In other words, the patient would speak his thoughts out loud in order to re-give himself the feeling of agency as he could hear himself speaking and then contributing the thought to himself.

"Entgleisen" (derailment in German) was first used with this meaning by Carl Schneider in 1930. The term "asyndesis" was introduced by N. Cameron in 1938, while "loosening of association" was introduced by A. Bleuler in 1950. The phrase "knight's move thinking" was first used in the context of pathological thinking by the psychologist Peter McKellar in 1957, who hypothesized that schizophrenics fail to suppress divergent associations. "Derailment" was used with this meaning by Kurt Schneider in 1959.

A self-disorder, also called ipseity disturbance, is a psychological phenomenon of disruption or diminishing of a person's sense of minimal (or basic) self. The sense of minimal self refers to the very basic sense of having experiences that are one's own; it has no properties, unlike the more extended sense of self, the narrative self, which is characterized by the person's reflections on themselves as a person, things they like, their identity, and other aspects that are the result of reflection on one's self. Disturbances in the sense of minimal self, as measured by the Examination of Anomalous Self-Experience (EASE), aggregate in the schizophrenia spectrum disorders, to include schizotypal personality disorder, and distinguish them from other conditions such as psychotic bipolar disorder and borderline personality disorder.

The use of antipsychotic medication is commonly the first line of treatment; however, the effectiveness after treatment is in question.

L-DOPA is effective against reduced affect display and emotional withdrawal, aloofness from society, apathy.

Neurosis is a class of functional mental disorders involving chronic distress but neither delusions nor hallucinations. The term is no longer used by the professional psychiatric community in the United States, having been eliminated from the "Diagnostic and Statistical Manual of Mental Disorders" in 1980 with the publication of DSM III. It is still used in the .

Neurosis should not be mistaken for psychosis, which refers to a loss of touch with reality. Neither should it be mistaken for neuroticism, a fundamental personality trait proposed in the big Five personality traits theory.

The concept of thought disorder has been criticized as being based on circular or incoherent definitions. For example, thought disorder is inferred from disordered speech, based on the assumption that disordered speech arises because of disordered thought. Incoherence, or word salad, refers to speech that is unconnected and conveys no meaning to the listener.

Furthermore, although thought disorder is typically associated with psychosis, similar phenomena can appear in different disorders, potentially leading to misdiagnosis—for example, in the case of incomplete yet potentially fruitful thought processes.

It has been suggested that individuals with autism spectrum disorders (ASD) display language disturbances like those found in schizophrenia; a 2008 study found that children and adolescents with ASD showed significantly more illogical thinking and loose associations than control subjects. The illogical thinking was related to cognitive functioning and executive control; the loose associations were related to communication symptoms and to parent reports of stress and anxiety.

In psychology and psychiatry, clanging refers to a mode of speech characterized by association of words based upon sound rather than concepts. For example, this may include compulsive rhyming or alliteration without apparent logical connection between words. This is associated with the irregular thinking apparent in psychotic mental illnesses (e.g. mania and schizophrenia). Gustav Aschaffenburg found that manic individuals generated these "clang-associations" roughly 10-50 times more than non-manic individuals. Aschaffenburg also found that the frequency of these associations increased for all individuals as they became more fatigued.

Clanging refers specifically to behavior that is situationally inappropriate. While a poet rhyming is not evidence of mental illness, disorganized speech that impedes the patient's ability to communicate is a disorder in itself, often seen in schizophrenia.

Risk factors (constructs which increase the likelihood or intensity of homesickness) and protective factors (constructs that decrease the likelihood or intensity of homesickness) vary by population. For example, a seafarers on board, the environmental stressors associated with a hospital, a military boot camp or a foreign country may exacerbate homesickness and complicate treatment. Generally speaking, however, risk and protective factors transcend age and environment.

The risk factors for homesickness fall into five categories: experience, personality, family, attitude and environment. More is known about some of these factors in adults—especially personality factors—because more homesickness research has been performed with older populations. However, a growing body of research is elucidating the etiology of homesickness in younger populations, including children at summer camp, hospitalized children and students.

- Experience factors: Younger age; little previous experience away from home (for which age can be a proxy); little or no previous experience in the novel environment; little or no previous experience venturing out without primary caregivers.

- Attitude factors: The belief that homesickness will be strong; negative first impressions and low expectations for the new environment; perceived absence of social support; high perceived demands (e.g., on academic, vocational or sports performance); great perceived distance from home

- Personality factors: Insecure attachment relationship with primary caregivers; low perceived control over the timing and nature of the separation from home; anxious or depressed feelings in the months prior to the separation; low self-directedness; high harm avoidance; rigidity; a wishful-thinking coping style.

- Family factors: Low decision control (e.g., caregivers forcing a young child to spend time away from home against her wishes); governments forcing a person to be in a novel environment (e.g., being drafted into military service away from home or being sentenced to prison); unsupportive caregiving; caregivers who express anxiety or ambivalence about the separation (e.g., "Have a great time away. I don't know what I'll do without you.")

- Environmental factors: High cultural contrast (e.g., different language, customs, food); threats to physical and emotional safety; dramatic alternations in daily schedule; lack of information about the new place; perceived discrimination

Finally, research has provided no support for a few factors that conventional wisdom had once held to be risk factors. These include: recent separation or divorce of primary caregivers; geographic distance from home; or recent geographic move. Most likely, it is not a change in family structure, distance or dwelling that predicts homesickness, but whether these changes have left unanswered (potentially preoccupying) questions in the person's mind.

Thought insertion is defined by the ICD-10 as feeling as if one's thoughts are not one's own, but rather belong to someone else and have been inserted into one's mind. The person experiencing thought insertion will not necessarily know where the thought is coming from, but is able to distinguish between their own thoughts and those inserted into their minds. However, patients do not experience all thoughts as inserted, only certain ones, normally following a similar content or pattern. This phenomenon is classified as a delusion. A person with this delusional belief is convinced of the veracity of their beliefs and is unwilling to accept such diagnosis.

Thought insertion is a common symptom of psychosis and occurs in many mental disorders and other medical conditions. However, thought insertion is most commonly associated with schizophrenia. Thought insertion, along with thought broadcasting, thought withdrawal, thought blocking and other first rank symptoms, is a primary symptom and should not be confused with the delusional explanation given by the respondent. Although normally associated with some form of psychopathology, thought insertion can also be experienced in those considered nonpathological, usually in spiritual contexts, but also in culturally influenced practices such as mediumship and automatic writing.

Examples of thought insertion:

"She said that sometimes it seemed to be her own thought 'but I don't get the feeling that it is'. She said her 'own thoughts might say the same thing', 'but the feeling isn't the same', 'the feeling is that it is somebody else's'"

"I look out the window and I think that the garden looks nice and the grass looks cool, but the thoughts of Eamonn Andrews come into my mind. There are no other thoughts there, only his. He treats my mind like a screen and flashes thoughts onto it like you flash a picture"

"The subject has thoughts that she thinks are the thoughts of other people, somehow occurring in her own mind. It is not that the subject thinks that other people are making her think certain thoughts as if by hypnosis or psychokinesis, but that other people think the thoughts using the subject's mind as a psychological medium."

The minimal self has been likened to a "flame that enlightens its surroundings and thereby itself." Unlike the extended self, which is composed of properties such as the person's identity, the person's narrative, and other aspects that can be gleaned from reflection, the minimal self has no properties, but refers to the "mine-ness" "given-ness" of experience, that the experiences are that of the person having them in that person's stream of consciousness. These experiences that are part of the minimal self are normally "tacit" and implied, requiring no reflection on the part of the person experiencing to know that the experience is theirs. The minimal self cannot be further elaborated and normally one cannot grasp it upon reflection. The minimal self goes hand-in-hand with immersion in the shared social world, such that "[t]he world is always pregiven, ie, tacitly grasped as a self-evident background of all experiencing and meaning." This is the self-world structure.

De Warren gives an example of the minimal self combined with immersion in the shared social world: "When looking at this tree in my backyard, my consciousness is directed toward the tree and not toward my own act of perception. I am, however, aware of myself as perceiving this tree, yet this self-awareness (or self-consciousness) is not itself thematic." The focus is normally on the tree itself, not on the person's own act of seeing the tree: to know that one is seeing the tree does not require an act of reflection.

In her final book, "Neurosis and Human Growth", Karen Horney laid out a complete theory of the origin and dynamics of neurosis. In her theory, neurosis is a distorted way of looking at the world and at oneself, which is determined by compulsive needs rather than by a genuine interest in the world as it is. Horney proposed that neurosis is transmitted to a child from his or her early environment and that there are many ways in which this can occur:

The child's initial reality is then distorted by his or her parents' needs and pretenses. Growing up with neurotic caretakers, the child quickly becomes insecure and develops basic anxiety. To deal with this anxiety, the child's imagination creates an idealized self-image:

Once he identifies himself with his idealized image, a number of effects follow. He will make claims on others and on life based on the prestige he feels entitled to because of his idealized self-image. He will impose a rigorous set of standards upon himself in order to try to measure up to that image. He will cultivate pride, and with that will come the vulnerabilities associated with pride that lacks any foundation. Finally, he will despise himself for all his limitations. Vicious circles will operate to strengthen all of these effects. Eventually, as he grows to adulthood, a particular "solution" to all the inner conflicts and vulnerabilities will solidify. He will be expansive and will display symptoms of narcissism, perfectionism, or vindictiveness. Or he will be self-effacing and compulsively compliant; he will display symptoms of neediness or codependence. Or he will be resigned and will display schizoid tendencies.

In Horney's view, mild anxiety disorders and full-blown personality disorders all fall under her basic scheme of neurosis as variations in the degree of severity and in the individual dynamics.The opposite of neurosis is a condition Horney calls self-realization, a state of being in which the person responds to the world with the full depth of his or her spontaneous feelings, rather than with anxiety-driven compulsion. Thus the person grows to actualize his or her inborn potentialities. Horney compares this process to an acorn that grows and becomes a tree.

STPD is rarely seen as the primary reason for treatment in a clinical setting, but it often occurs as a comorbid finding with other mental disorders. When patients with STPD are prescribed pharmaceuticals, they are most often prescribed the same drugs used to treat patients suffering from schizophrenia including traditional neuroleptics such as haloperidol and thiothixene. In order to decide which type of medication should be used, Paul Markovitz distinguishes two basic groups of schizotypal patients:

- Schizotypal patients who appear to be almost schizophrenic in their beliefs and behaviors (aberrant perceptions and cognitions) are usually treated with low doses of antipsychotic medications, e.g. thiothixene. However, it must be mentioned that long-term efficacy of neuroleptics is doubtful.

- For schizotypal patients who are more obsessive-compulsive in their beliefs and behaviors, SSRIs like Sertraline appear to be more effective.

Lamotrigine, an anti-convulsant, appears to be helpful in dealing with social isolation.

To date, cognitive behavioral therapy (CBT) is the best established treatment for a variety of somatoform disorders including somatization disorder. CBT aims to help patients realize their ailments are not catastrophic and to enable them to gradually return to activities they previously engaged in, without fear of "worsening their symptoms". Consultation and collaboration with the primary care physician also demonstrated some effectiveness. The use of antidepressants is preliminary but does not yet show conclusive evidence. Electroconvulsive shock therapy (ECT) has been used in treating somatization disorder among the elderly; however, the results were still debatable with some concerns around the side effects of using ECT. Overall, psychologists recommend addressing a common difficulty in patients with somatization disorder in the reading of their own emotions. This may be a central feature of treatment; as well as developing a close collaboration between the GP, the patient and the mental health practitioner.

Some debates have pervaded the field of psychology since its genesis. Perhaps one of the most salient ones deals with the nature of personality. Personality psychology studies one's distinctive style of cognition, behavior, and affect. However, this concept elicits discord among psychologists as some have insisted that it does not exist, while others struggle with issues of measurement.

An example of circumstantial speech is that when asked about the age of a person's mother at death, the speaker responds by talking at length about accidents and how too many people die in accidents, then eventually says what the mother's age was at death.

According to Theodore Millon, the schizotypal is one of the easiest personality disorders to identify but one of the most difficult to treat with psychotherapy. Persons with STPD usually consider themselves to be simply eccentric, productive, or nonconformist. As a rule, they underestimate maladaptiveness of their social isolation and perceptual distortions. It is not so easy to gain rapport with people who suffer from STPD due to the fact that increasing familiarity and intimacy usually increase their level of anxiety and discomfort. In most cases they do not respond to informality and humor.

Group therapy is recommended for persons with STPD only if the group is well structured and supportive. Otherwise, it could lead to loose and tangential ideation. Support is especially important for schizotypal patients with predominant paranoid symptoms, because they will have a lot of difficulties even in highly structured groups.

Ideas of reference and delusions of reference describe the phenomenon of an individual's experiencing innocuous events or mere coincidences and believing they have strong personal significance. It is "the notion that everything one perceives in the world relates to one's own destiny".

In psychiatry, delusions of reference form part of the diagnostic criteria for psychotic illnesses such as schizophrenia, delusional disorder, bipolar disorder (during the elevated stages of mania), as well as schizotypal personality disorder. To a lesser extent, it can be a hallmark of paranoid personality disorder. Such symptoms can also be caused by intoxication, especially with hallucinogens or stimulants like methamphetamine.

Low frustration tolerance (LFT), or "short-term hedonism" is a concept utilized to describe the inability to tolerate unpleasant feelings or stressful situations. It stems from the feeling that reality should be as wished, and that any frustration should be resolved quickly and easily. People with low frustration tolerance experience emotional disturbance when frustrations are not quickly resolved. Behaviors are then directed towards avoiding frustrating events which, paradoxically, leads to increased frustration and even greater mental stress.

In REBT the opposite construct is "high frustration tolerance".

Treatment for perfectionism can be approached from many therapeutic directions. Some examples of psychotherapy include: cognitive-behavioral therapy (the challenging of irrational thoughts and formation of alternative ways of coping and thinking), psychoanalytic therapy (an analysis of underlying motives and issues), group therapy (where two or more clients work with one or more therapists about a specific issue, this is beneficial for those who feel as if they are the only one experiencing a certain problem), humanistic therapy (person-centered therapy where the positive aspects are highlighted), and self-therapy (personal time for the person where journaling, self-discipline, self-monitoring, and honesty with self are essential). Cognitive-behavioral therapy has been shown to successfully help perfectionists in reducing social anxiety, public self-consciousness, and perfectionism. By using this approach, a person can begin to recognize his or her irrational thinking and find an alternative way to approach situations. Cognitive-behavioral therapy is intended to help the person understand that it is okay to make mistakes sometimes and that those mistakes can become lessons learned.

Psychiatrist Kantor suggests a treatment approach using psychodynamic, supportive, cognitive, behavioral and interpersonal therapeutic methods. These methods apply to both the Passive–aggressive person and their target victim.

The WHO first listed the condition in the 6th revision of the International Classification of Diseases ICD-6 (1949) and it stayed in the manual until the present version ICD-10.