Causes of mental disorders

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A mental disorder is "a clinically significant behavioral or psychological syndrome or psychological pattern that occurs in an individual and that is associated with present disability or with a significantly increased risk of suffering, death, pain, disability, or an important loss of freedom."

The causes of mental disorders are regarded as complex and varying depending on the particular disorder and the individual. Although the causes of most mental disorders are not fully understood, researchers have identified a variety of biological, psychological, and environmental factors that can contribute to the development or progression of mental disorders. Most mental disorders are a result of a combination of several different factors rather than just a single factor.

Research results

Risk factors for mental illness include, psychological trauma, adverse childhood environments, and genetic predisposition and personality traits. Correlations of mental disorders with drug use include almost all psychoactive substances, e.g., cannabis, alcohol and caffeine.

Particular mental illnesses have particular risk factors, for instance including unequal parental treatment, adverse life events and drug use in depression, migration and discrimination, childhood trauma, bereavement or separation in families, and cannabis use in schizophrenia and psychosis, and parenting factors, child abuse, family history (e.g. of anxiety), and temperament and attitudes (e.g. pessimism) in anxiety. Many psychiatric disorders include problems with impulse and other emotional control. 

In February 2013 a study found common genetic links between five major psychiatric disorders: autism, ADHD, bipolar disorder, major depressive disorder, and schizophrenia. Abnormal functioning of neurotransmitter systems has been implicated in several mental disorders, including serotonin, norepinephrine, dopamine and glutamate systems. Differences have also been found in the size or activity of certain brain regions in some cases. Psychological mechanisms have also been implicated, such as cognitive (e.g. reasoning) biases, emotional influences, personality dynamics, temperament and coping style. Studies have indicated that variation in genes can play an important role in the development of mental disorders, although the reliable identification of connections between specific genes and specific categories of disorder has proven more difficult. Environmental events surrounding pregnancy and birth have also been implicated. Traumatic brain injury may increase the risk of developing certain mental disorders. There have been some tentative inconsistent links found to certain viral infections, to substance misuse, and to general physical health.

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

Theories

General theories

There are a number of theories or models seeking to explain the causes (etiology) of mental disorders. These theories may differ in regards to how they explain the cause of the disorder, how they treat the disorder, and their basic classification of mental disorders. There may also be differences in philosophy of mind regarding whether, or how, the mind is considered separately from the brain. 

During most of the 20th century, mental illness was believed to be caused by problematic relationships between children and their parents. This view was held well into the late 1990s, in which people still believed this child-parent relationship was a large determinant of severe mental illness, such as depression and schizophrenia. Today,  the belief is held that the child-parent relationship is of small importance in terms of causing mental illness compared to biological and genetic factors. So, the perceived causes of mental illness have changed over time and will most likely continue to alter while more research is done in this area.

Outside the West, community approaches remain a focus.

Medical or biomedical model

An overall distinction is also commonly made between a "medical model" (also known as a biomedical or disease model) and a "social model" (also known as an empowerment or recovery model) of mental disorder and disability, with the former focusing on hypothesized disease processes and symptoms, and the latter focusing on hypothesized social constructionism and social contexts.

Biological psychiatry has tended to follow a biomedical model focused on organic or "hardware" pathology of the brain, 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.

Biopsychosocial model

The primary model of contemporary mainstream Western psychiatry is the biopsychosocial model (BPS), which merges biological, psychological and social factors. For instance one view is that genetics accounts for 40% of a person's susceptibility to mental disorders while psychological and environmental factors account for the other 60%. It may be commonly neglected or misapplied in practice due to being too broad or relativistic, however. 

The most common view  is that disorders tend to result from genetic dispositions and environmental stressors, combining to cause patterns of distress or dysfunction or, more sharply, trigger disorders (Diathesis-stress model). A practical mixture of models may often be used to explain particular issues and disorders, although there may be difficulty defining boundaries for indistinct psychiatric syndromes.

Psychoanalytic theories

Psychoanalytic theories focus on unresolved internal and relational conflicts. These theories have been posited as overall explanations of mental disorder, although today most psychoanalytic groups are said to adhere to the biopsychosocial model and to accept an eclectic mix of subtypes of psychoanalysis. The psychoanalytic theory was originated by Sigmund Freud. This theory focuses on the impact of unconscious forces on human behavior. According to Freud, the personality is made up of three parts: the id, ego, and superego. The id operates under the pleasure principle, the ego operates under the reality principle, and the superego is the "conscience" and incorporates what is and is not socially acceptable into a person's value system. Also, according to the psychoanalytic theory, there are five stages of psycho-sexual development that everyone goes through: the oral stage, anal stage, phallic stage, latency stage, and genital stage. Mental disorders can be caused by an individual receiving too little or too much gratification in one of the psycho-sexual developmental stages. When this happens, the individual is said to be fixated in that developmental stage.

Attachment theory

Attachment theory is a kind of evolutionary-psychological approach sometimes applied in the context for mental disorders, which focuses on the role of early caregiver-child relationships, responses to danger, and the search for a satisfying reproductive relationship in adulthood. According to this theory, the more secure a child's attachment is to a nurturing adult, the more likely that child will maintain healthy relationships with others in their life. As found by the Strange Situation experiment run by Mary Ainsworth based on the formulations of John Bowlby, there are four main patterns of attachment: secure attachment, avoidant attachment, disorganized attachment and ambivalent attachment. These attachment patterns are found cross-culturally. Later research found a fourth pattern of attachment known as disorganized disoriented attachment. Secure attachments reflect trust in the child-caretaker relationship while insecure attachment reflects mistrust. The security of attachment in a child affects the child's emotional, cognitive, and social competence later in life.

Evolutionary psychology

Evolutionary psychology (or more specifically evolutionary psychopathology or psychiatry) has also been proposed as an overall theory, positing that many mental disorders involve the dysfunctional operation of mental modules adapted to ancestral physical or social environments but not necessarily to modern ones. Other theories suggest that mental illness could have evolutionary advantages for the species, including in enhancing creativity. Some related behavioral abnormalities have been found in non-human great apes. Evolutionary psychology applies Darwinian principles to human behavior by saying that human minds are products of natural selection and have specific functions. Humans strive to carry on their genetic legacy through their offspring. This theory identifies the environment as having a great effect on a person's mental development.

Factors affecting choice of models and theories

Psychiatrists may favour biomedical models because they believe such models make their discipline seem more esteemed. Similarly, families of mentally ill people tend to favour biomedical models because to do so gives less self-blame. If patients are seen by a more ethnically similar doctor, they are more likely to adopt a non-biomedical model.

Biological factors

Biological factors consist of anything physical that can cause adverse effects on a person's mental health. This includes genetics, prenatal damage, infections, exposure to toxins, brain defects or injuries, and substance abuse. Many professionals believe that the sole cause of mental disorders is based upon the biology of the brain and the nervous system.

Mind mentions genetic factors, long-term physical health conditions, and head injuries or epilepsy (affecting behaviour and mood) as factors that may possibly trigger an episode of mental illness.

Genetics

Family-linkage and twin studies have indicated that genetic factors often play an important role in the development of mental disorders. The reliable identification of specific genetic susceptibility to particular disorders, through linkage or association studies, has proven difficult. This has been reported to be likely due to the complexity of interactions between genes, environmental events, and early development or to the need for new research strategies. The heritability of behavioral traits associated with mental disorder may be greater in permissive than in restrictive environments, and susceptibility genes probably work through both "within-the-skin" (physiological) pathways and "outside-the-skin" (behavioral and social) pathways. Investigations increasingly focus on links between genes and endophenotypes—more specific traits (including neurophysiological, biochemical, endocrinological, neuroanatomical, cognitive, or neuropsychological)—rather than disease categories. With regard to a prominent mental disorder, schizophrenia, for a long time consensus among scientists was that certain alleles (forms of genes) were responsible for schizophrenia, but some research has indicated only multiple, rare mutations thought to alter neurodevelopmental pathways that can ultimately contribute to schizophrenia; virtually every rare structural mutation was different in each individual.

Research has shown that many conditions are polygenic meaning there are multiple defective genes rather than only one that are responsible for a disorder. Schizophrenia and Alzheimer's are both examples of hereditary mental disorders.

The increasing understanding of brain plasticity (neuroplasticity) raises questions of whether some brain differences may be caused by mental illnesses, rather than pre-existing and causing them.

Prenatal damage

Any damage that occurs to a fetus while still in its mother's womb is considered prenatal damage. If the pregnant mother uses drugs or alcohol or is exposed to illnesses or infections then mental disorders can develop in the fetus. According to research, certain conditions, such as autism result from a disruption of early fetal brain progression.

Environmental events surrounding pregnancy and birth have been linked to an increased development of mental illness in the offspring. This includes maternal exposure to serious psychological stress or trauma, conditions of famine, obstetric birth complications, infections, and gestational exposure to alcohol or cocaine. Such factors have been hypothesized to affect specific areas of neurodevelopment within the general developmental context and to restrict neuroplasticity.

Infection, disease and toxins

A number of psychiatric disorders have often been tentatively linked with microbial pathogens, particularly viruses; however while there have been some suggestions of links from animal studies, and some inconsistent evidence for infectious and immune mechanisms (including prenatally) in some human disorders, infectious disease models in psychiatry are reported to have not yet shown significant promise except in isolated cases.

There have been some inconsistent findings of links between infection by the parasite Toxoplasma gondii and human mental disorders such as schizophrenia, with the direction of causality unclear. A number of diseases of the white matter can cause symptoms of mental disorder.

Poorer general health has been found among individuals with severe mental illnesses, thought to be due to direct and indirect factors including diet, bacterial infections, substance use, exercise levels, effects of medications, socioeconomic disadvantages, lowered help-seeking or treatment adherence, or poorer healthcare provision. Some chronic general medical conditions have been linked to some aspects of mental disorder, such as AIDS-related psychosis. 

The current research on Lyme's disease caused by a deer tick, and related toxins, is expanding the link between bacterial infections and mental illness.

Research shows that infections and exposure to toxins such as HIV and streptococcus cause dementia and OCD respectively. The infections or toxins trigger a change in the brain chemistry, which can develop into a mental disorder.

Injury and brain defects

Any damage to the brain can cause a mental disorder. The brain is the control system for the nervous system and the rest of the body. Without it the body cannot function properly.

Higher rates of mood, psychotic, and substance abuse disorders have been found following traumatic brain injury (TBI). Findings on the relationship between TBI severity and prevalence of subsequent psychiatric disorders have been inconsistent, and occurrence has been linked to prior mental health problems as well as direct neurophysiological effects, in a complex interaction with personality and attitude and social influences.

Head trauma is classified as either open or closed head injury. In open head injury the skull is penetrated and brain tissue is destroyed in a localized area. Closed head injury is more common, the skull is not penetrated but there is an impact of the brain against the skull which can create permanent structural damage (e.g. subdural hematoma). With both types, symptoms may disappear or persist over time. It has been found that typically the longer the length of time spent unconscious and the length of post-traumatic amnesia the worse the prognosis for the individual. The cognitive residual symptoms of head trauma are associated with the type of injury (either open head injury or closed head injury)and the amount of tissue destroyed. Symptoms of closed injury head trauma tend to be the experience of intellectual deficits in abstract reasoning ability, judgement, and memory, and also marked personality changes. Symptoms of open injury head trauma tend to be the experience of classic neuropsychological syndromes like aphasia, visual-spatial disorders, and types of memory or perceptual disorders.

Brain tumors are classified as either malignant and benign, and as intrinsic (directly infiltrate the parenchyma of the brain) or extrinsic (grows on the external surface of the brain and produces symptoms as a result of pressure on the brain tissue). Progressive cognitive changes associated with brain tumors may include confusion, poor comprehension, and even dementia. Symptoms tend to depend on the location of the tumor on the brain. For example, tumors on the frontal lobe tend to be associated with the symptoms of impairment of judgment, apathy, and loss of the ability to regulate/modulate behavior.

Findings have indicated abnormal functioning of brainstem structures in individuals with mental disorders such as schizophrenia, and other disorders that have to do with impairments in maintaining sustained attention. Some abnormalities in the average size or shape of some regions of the brain have been found in some disorders, reflecting genes and/or experience. Studies of schizophrenia have tended to find enlarged ventricles and sometimes reduced volume of the cerebrum and hippocampus, while studies of (psychotic) bipolar disorder have sometimes found increased amygdala volume. Findings differ over whether volumetric abnormalities are risk factors or are only found alongside the course of mental health problems, possibly reflecting neurocognitive or emotional stress processes and/or medication use or substance use. Some studies have also found reduced hippocampal volumes in major depression, possibly worsening with time depressed.

Neurotransmitter systems

Abnormal levels of dopamine activity have been correlated with a number of disorders (e.g., reduced in ADHD and OCD, and increased in schizophrenia). Dysfunction in serotonin and other monoamine neurotransmitters (e.g., norepinephrine and dopamine), and their associated neural networks, are also moderately correlated with certain mental disorders, including major depression, obsessive compulsive disorder, phobias, posttraumatic stress disorder, and generalized anxiety disorder. Studies of depleted levels of monoamine neurotransmitters show an association with depression and other psychiatric disorders, but "... it should be questioned whether 5-HT [serotonin] represents just one of the final, and not the main, factors in the neurological chain of events underlying psychopathological symptoms...." 

Simplistic "chemical imbalance" explanations for mental disorders have never received empirical support; and most prominent psychiatrists, neuroscientists, and psychologists have not espoused such ill-defined, facile etiological theories. Instead, neurotransmitter systems have been understood in the context of the diathesis-stress or biopsychosocial models. The following 1967 quote from renowned psychiatric and neuroscience researchers exemplifies this more sophisticated understanding (in contrast to the woolly "chemical imbalance" notion).

Whereas specific genetic factors may be of importance in the etiology of some, and possibly all, depressions, it is equally conceivable that early experiences of the infant or child may cause enduring biochemical changes, and that these may predispose some individuals to depressions in adulthood. It is not likely that changes in the metabolism of the biogenic amines alone will account for the complex phenomena of normal or pathological affect.

Substance abuse

Substance abuse, especially long-term abuse, can cause or exacerbate many mental disorders. Alcoholism is linked to depression while abuse of amphetamines and LSD can leave a person feeling paranoid and anxious.

Correlations of mental disorders with drug use include cannabis, alcohol and caffeine. Caffeine use is correlated with anxiety and suicide. Illicit drugs have the ability to stimulate particular parts of the brain which can affect development in adolescence. Cannabis has been found to worsen depression and lessen an individual's motivation. Alcohol has the potential to damage "white matter" in the brain which affects thinking and memory. Alcohol has been found to be a serious problem in many countries due to many people participating in excessive drinking or binge drinking.

Life experience and environmental factors

The term "environment" is very loosely defined when it comes to mental illness. Unlike biological and psychological causes, environmental causes are stressors that individuals deal with in everyday life. These stressors range from financial issues to having low self-esteem. Environmental causes are more psychologically based thus making them more closely related. Events that evoke feelings of loss or damage are most likely to cause a mental disorder to develop in an individual. Environmental factors include but are not limited a dysfunctional home life, poor relationships with others, substance abuse, not meeting social expectations, low self-esteem and poverty.

Mind mentions childhood abuse, trauma, violence or neglect, social isolation, loneliness or discrimination, the death of someone close, stress, homelessness or poor housing, social disadvantage, poverty or debt, unemployment, caring for a family member or friend, significant trauma as an adult, such as military combat, and being involved in a serious accident or being the victim of a violent crime as possibly triggering an episode of mental illness.

Repeating generational patterns have been found to be a risk factor for mental illness.

Life events and emotional stress

It is reported that treatment in childhood and in adulthood, including sexual abuse, physical abuse, emotional abuse, domestic violence and bullying, has been linked to the development of mental disorders, through a complex interaction of societal, family, psychological and biological factors. Negative or stressful life events more generally have been implicated in the development of a range of disorders, including mood and anxiety disorders. The main risks appear to be from a cumulative combination of such experiences over time, although exposure to a single major trauma can sometimes lead to psychopathology, including PTSD. Resilience to such experiences varies, and a person may be resistant to some forms of experience but susceptible to others. Features associated with variations in resilience include genetic vulnerability, temperamental characteristics, cognitive set, coping patterns, and other experiences.

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.

Poor parenting, abuse and neglect

Poor parenting has been found to be a risk factor for depression and anxiety. Separation or bereavement in families, and childhood trauma, have been found to be risk factors for psychosis and schizophrenia.

Severe psychological trauma such as abuse can wreak havoc on a person's life. Children are much more susceptible to psychological harm from traumatic events than adults. Once again, the reaction to the trauma will vary based on the person as well as the individual's age. The impact of these events is influenced by several factors: the type of event, the length of exposure the individual had to the event, and the extent to which the individual and their family/friends were personally affected by the event. Human-caused disasters, such as a tumultuous childhood affect children more than natural disasters.

Neglect is a type of maltreatment related to the failure to provide needed, age-appropriate care, supervision and protection. It is not to be confused with abuse, which, in this context, is defined as any action that intentionally harms or injures another person. Neglect most often happens during childhood by the parents or caretakers. Oftentimes, parents who are guilty of neglect were also neglected as children. The long-term effects of neglect are reduced physical, emotional, and mental health in a child and throughout adulthood.

The Adverse Childhood Experiences Study

Adverse childhood experiences (ACEs) are various forms of maltreatment and household dysfunction experienced in childhood. The Adverse Childhood Experiences Study has shown a strong dose–response relationship between ACEs and numerous health, social, and behavioral problems throughout a person's lifespan, including suicide attempts and frequency of depressive episodes. Children's neurological development can be disrupted when they are chronically exposed to stressful events such as physical, emotional, or sexual abuse, physical or emotional neglect, witnessing violence in the household, or a parent being incarcerated or suffering from a mental illness. As a result, the child's cognitive functioning or ability to cope with negative or disruptive emotions may be impaired. Over time, the child may adopt various harmful coping strategies that can contribute to later disease and disability.

Relationships

Relationship issues have been consistently linked to the development of mental disorders, with continuing debate on the relative impact of the home environment or work/school and peer groups. Issues with parenting skills or parental depression or other problems may be a risk factor. Parental divorce appears to increase risk, perhaps only if there is family discord or disorganization, although a warm supportive relationship with one parent may compensate. Details of infant feeding, weaning, toilet training etc. do not appear to be importantly linked to psychopathology. Early social privation, or lack of ongoing, harmonious, secure, committed relationships, have been implicated in the development of mental disorders.

Some approaches, such as certain theories of co-counseling, may see all non-neurological mental disorders as the result of the self-regulating mechanisms of the mind (which accompany the physical expression of emotions) not being allowed to operate. 

How an individual interacts with others as well as the quality of relationships can greatly increase or decrease a person's quality of living. Continuous fighting with friends and family can all lead to an increased risk of developing a mental illness. A dysfunctional family may include disobedience, child neglect and/or abuse which occurs regularly. These types of families are often a product of an unhealthy co-dependent relationship on the part of the head of the household (usually to drugs). 

Losing a loved one, especially at an early age can have lasting effects on an individual. The individual may feel fear, guilt, anger or loneliness. This can drive a person into solitude and depression. They may turn to alcohol and drugs to cope with their feelings. 

Divorce is also another factor that can take a toll on both children and adults alike. Divorcees may suffer from emotional adjustment problems due to a loss of intimacy and social connections. Newer statistics show that the negative effects of divorce have been greatly exaggerated. The effects of divorce in children are based on three main factors: the quality of their relationship with each of their parents before the separation, the intensity and duration of the parental conflict, and the parents' ability to focus on the needs of children in their divorce.

Social expectations and esteem

How individuals view themselves ultimately determines who they are, their abilities and what they can be. Having both too low of self-esteem as well as too high of one can be detrimental to an individual's mental health. A person's self-esteem plays a much larger role in their overall happiness and quality of life. Poor self-esteem whether it be too high or too low can result in aggression, violence, self-deprecating behavior, anxiety, and other mental disorders. 

Not fitting in with the masses can result in bullying and other types of emotional abuse. Bullying can result in depression, feelings of anger, loneliness.

Poverty

Studies show that there is a direct correlation between poverty and mental illness. The lower the socioeconomic status of an individual the higher the risk of mental illness. Impoverished people are actually two to three times more likely to develop mental illness than those of a higher economic class. 

Low levels of self-efficiency and self-worth are commonly experienced by children of disadvantaged families or those from the economic underclass. Theorists of child development have argued that persistent poverty leads to high levels of psychopathology and poor self-concepts.

This increased risk for psychiatric complications remains consistent for all individuals among the impoverished population, regardless of any in-group demographic differences that they may possess. These families must deal with economic stressors like unemployment and lack of affordable housing, which can lead to mental health disorders. A person's socioeconomic class outlines the psychosocial, environmental, behavioral, and biomedical risk factors that are associated with mental health.

According to findings there is a strong association between poverty and substance abuse. Substance abuse only perpetuates a continuous cycle. It can make it extremely difficult for individuals to find and keep jobs. As stated earlier, both financial problems and substance abuse can cause mental illnesses to develop.

Communities and cultures

Mental disorders have been linked to the overarching social, economic and cultural system. Some non-Western views take this community approach.

Problems in communities or cultures, including poverty, unemployment or underemployment, lack of social cohesion, and migration, have been associated with the development of mental disorders. Stresses and strains related to socioeconomic position (socioeconomic status (SES) or social class) have been linked to the occurrence of major mental disorders, with a lower or more insecure educational, occupational, economic or social position generally linked to more mental disorders. There have been mixed findings on the nature of the links and on the extent to which pre-existing personal characteristics influence the links. Both personal resources and community factors have been implicated, as well as interactions between individual-level and regional-level income levels. The causal role of different socioeconomic factors may vary by country. Socioeconomic deprivation in neighborhoods can cause worse mental health, even after accounting for genetic factors. In addition, minority ethnic groups, including first or second-generation immigrants, have been found to be at greater risk for developing mental disorders, which has been attributed to various kinds of life insecurities and disadvantages, including racism. The direction of causality is sometimes unclear, and alternative hypotheses such as the Drift Hypothesis sometimes need to be discounted.

Psychological and individual factors, including resilience

Some clinicians believe that psychological characteristics alone determine mental disorders. Others speculate that abnormal behavior can be explained by a mix of social and psychological factors. In many examples, environmental and psychological triggers complement one another resulting in emotional stress, which in turn activates a mental illness Each person is unique in how they will react to psychological stressors. What may break one person may have little to no effect on another. Psychological stressors, which can trigger mental illness, are as follows: emotional, physical or sexual abuse, loss of a significant loved one, neglect and being unable to relate to others.

The inability to relate to others is also known as emotional detachment. Emotional detachment makes it difficult for an individual to empathize with others or to share their own feelings. An emotionally detached person may try to rationalize or apply logic to a situation to which there is no logical explanation. These individuals tend to stress the importance of their independence and may be a bit neurotic. Oftentimes, the inability to relate to others stems from a traumatic event. 

Mental characteristics of individuals, as assessed by both neurological and psychological studies, have been linked to the development and maintenance of mental disorders. This includes cognitive or neurocognitive factors, such as the way a person perceives, thinks or feels about certain things; or an individual's overall personality, temperament or coping style or the extent of protective factors or "positive illusions" such as optimism, personal control and a sense of meaning.