Biological causes of mental illness

Genetics, prenatal damage, infections, toxin exposure, brain malformations or traumas, and substance use are all biological contributors. Many experts feel that the biology of the brain and nerve system is to blame for mental illnesses.Biological variables are any bodily aspects that can have a negative impact on a person's mental health. Genetics, prenatal damage, infections, toxin exposure, brain malformations or traumas, and substance use are all biological contributors. Many experts feel that the biology of the brain and nerve system is to blame for mental illnesses.

Genetic factors, long-term physical health disorders, and brain injuries or epilepsy (which impact behavior and mood) are all variables that can lead to a mental illness episode, according to Mind.


Genetic variables frequently play a role in the emergence of mental diseases, according to family linkage and some twin studies. It has been challenging to reliably identify specific genetic vulnerability to certain illnesses through linkage or association studies. This is due to the intricacy of gene-environment interactions and early development, as well as the necessity for innovative research methodologies. Susceptibility genes likely act through both "within-the-skin" (physiological) and "outside-the-skin" (behavioral and social) routes, and behavioral features associated with mental disorders may be more heritable in permissive than restrictive contexts. Because endophenotypes are more specific features, researchers are increasingly focusing on relationships between genes and endophenotypes. Rather than illness classifications, some include neurophysiological, biochemical, endocrinological, neuroanatomical, cognitive, or neuropsychological factors. It can be said with certainty that alleles (gene types) were responsible for a well-known mental illness called schizophrenia. According to several studies, only multiple, rare mutations are likely to affect neurodevelopmental pathways, which can eventually lead to schizophrenia; almost every rare structural alteration was different in each person.

According to research, many diseases are polygenic, which means that they are caused by numerous faulty genes rather than just one.

[requires citation] Hereditary mental diseases include schizophrenia and Alzheimer's disease.

The phenomenon of brain plasticity (neuroplasticity) begs the question of whether some brain variations are caused by mental diseases or if they are pre-existing and then cause them.

Prenatal harm

Prenatal damage refers to any harm to a fetus while it is still in its mother's womb. If a pregnant woman consumes drugs or alcohol, or is exposed to illnesses or infections during her pregnancy, mental issues can emerge. Autism is thought to be caused by a malfunction in early prenatal brain development, according to study.

The development of mental disorder in offspring has been linked to environmental factors around pregnancy and birth. Maternal stress or trauma, famine conditions, obstetric birth problems, infections, and prenatal exposure to alcohol or cocaine are all possible scenarios. These elements are thought to have an impact on neurodevelopment, general development, and neuroplasticity.

Toxins, infection, and illness

Microbial infections, notably viruses, have been linked to a variety of psychiatric diseases. There have been some hypotheses of correlations based on animal research, however the evidence for infectious and immunological pathways is contradictory. Except in exceptional circumstances, some human diseases, infectious disease models in psychiatry have not yet demonstrated substantial promise.

There have been some contradictory reports of correlations between Toxoplasma gondii infection and human mental diseases including schizophrenia, with the direction of causality unknown. Symptoms of mental illness can be caused by a variety of white matter illnesses.

Individuals with severe mental illnesses have been found to have poorer general health, which is thought to be due to both direct and indirect factors such as diet, bacterial infections, substance use, exercise levels, medication effects, socioeconomic disadvantages, reduced help-seeking or treatment adherence, or poorer healthcare provision. Various chronic general physical illnesses, such as AIDS-related psychosis, have been connected to some elements of mental disorders.

The relationship between bacterial illnesses and mental illness is becoming clearer because to new research on Lyme disease, which is spread by deer ticks and their toxins.

Infections and exposure to toxins like HIV and streptococcus have been linked to dementia and OCD, according to research.

[requires citation] Infections or poisons that cause a change in the brain's chemistry might cause mental illness.

Brain damage and deficiencies

A mental disorder can be caused by any harm to the brain. The neurological system and the rest of the body are controlled by the brain. The body cannot function correctly without it. [requires citation]

Traumatic brain injury (TBI) symptoms include mood swings, irrational behavior, and substance abuse disorders. The findings on the relationship between TBI severity and the occurrence of subsequent psychiatric diseases have been mixed, and occurrence is linked to previous mental health issues. In a complicated interaction with personality, attitude, and social influences, direct neurophysiological consequences are observed.

There are two types of brain trauma: open and closed. The skull is punctured and the brain tissue is destroyed in an open head injury. Closed head injuries are more common, and the skull is not ruptured because the brain collides with the skull, causing irreversible structural damage (subdural hematoma). Symptoms in both types may fade or persist over time. The longer an individual is unconscious and has post-traumatic amnesia, the worse their prognosis is. The type of damage (either an open head injury or a closed head injury) and the amount of tissue destroyed are linked to the cognitive residual symptoms of head trauma. Deficits in abstract reasoning abilities, judgment, memory, and noticeable personality changes are all indicators of closed damage head trauma. Classic neuropsychological syndromes such as aphasia, visual-spatial problems, and various memory or perceptual disorders are common indications of open injury head trauma.

Malignant and benign brain tumors are classed as intrinsic (infiltrate the brain's parenchyma directly) or extrinsic (infiltrate the brain's parenchyma indirectly) (grows on the external surface of the brain and produces symptoms as a result of pressure on the brain tissue). Confusion, poor comprehension, and even dementia are common cognitive impairments associated with brain tumors. The symptoms of a brain tumor vary depending on where it is located in the brain. Tumors in the frontal lobe, for example, are frequently associated with signs of impaired judgment, apathy, and a lack of the ability to regulate/modulate behavior.

Individuals with mental disorders such as schizophrenia and other disorders with problems in sustained attention have been found to have aberrant functioning of brainstem regions. In several illnesses, abnormalities in the average size or shape of some brain regions have been discovered, reflecting genes and experiences. In investigations of schizophrenia, enlarged ventricles and sometimes reduced cerebrum and hippocampal volume have been discovered, but studies of (psychotic) bipolar disorder have occasionally found increased amygdala volume. Volumetric abnormalities are either risk factors or only detected in the course of mental health disorders, presumably indicating neurocognitive or emotional stress processes as well as medication or substance use, according to the findings. Reduced hippocampus volumes have also been documented in several studies in those with serious depression, which may worsen with time.

System of neurotransmitters

Several illnesses are linked to abnormal levels of dopamine activation (reduced in ADHD and OCD, and increased in schizophrenia). Certain mental diseases and their related brain networks are linked to serotonin and other monoamine neurotransmitters (norepinephrine and dopamine) malfunction. Major depression, obsessive-compulsive disorder, phobias, post-traumatic stress disorder, and generalized anxiety disorder are just a few examples. Depleted levels of monoamine neurotransmitters have been linked to depression and other psychiatric disorders in studies, but "it should be questioned whether 5-HT [serotonin] represents just one of the final, rather than the main, factors in the neurological chain of events underlying psychopathological symptoms."

Simple "chemical imbalance" explanations for mental diseases have never been supported by empirical evidence, and the majority of eminent psychiatrists, neuroscientists, and psychologists have never advocated for such ill-defined, simplistic etiological ideas. Neurotransmitter systems have instead been studied in the context of diathesis-stress or biopsychosocial paradigms. This more comprehensive knowledge is exemplified by the following 1967 comment from famous psychiatry and neuroscience professionals (in contrast to the woolly "chemical imbalance" notion).

While certain genetic variables may play a role in the etiology of some, if not all, depressions, it is also possible that early experiences as an infant or child may result in long-term biochemical alterations that predispose some people to depression later in life. Changes in biogenic amine metabolism are unlikely to account for the complex phenomena of normal or diseased effect on their own.

Disorders of substance abuse

Substance abuse disorders, particularly long-term usage, can develop or exacerbate a variety of mental illnesses. A person's use of amphetamines and LSD might make them feel paranoid and agitated, while their use of alcohol is linked to depression.

Cannabis, alcohol, and caffeine consumption have all been linked to mental illnesses. Caffeine consumption is linked to anxiety and suicide. Illicit substances stimulate specific areas of the brain, which can impair adolescent growth. Cannabis has also been shown to exacerbate depression and reduce motivation. Alcohol has the ability to harm the brain's "white matter," which affects cognition and memory. Because many people engage in excessive or binge drinking, alcohol is an issue in many countries.