Lecture 9: Mental Illness
In the past weeks we have studied about the brain from various perspectives: we have looked at brain response to a physical activity, the chemistry behind it and seen the structure of the brain. This week we will discuss about mental illness.
Mental illness is defined as a diagnosable disorder of thought, mood or behavior that can cause distress or impaired functioning to the daily routine of an individual.
Psychosocial Approaches to Mental Illness
The emergence of psychiatry is said to be a crucial improvement in shaping a definition for mental illness. Psychiatry deals with disorders of human behavior and their treatments. An eminent Austrian psychiatrist and neurologist Sigmund Freud had a colossal impact in this emerging area. His theory of psychoanalysis is based on two main assumptions
- Much of mental life is unconscious.
- Former experiences, especially those of childhood, shape the personality of a person for their entire life.
Freud stated that mental illness is the result of the clash of unconscious and conscious elements of the psyche, and hence to treat a person with mental illness, the secret must be exposed.
Psychologist B.F. Skinner proposed a contrasting theory which assumed that many behaviors are learned responses to the environment. In other words, an individual learns to repeat a behavior if the following sensation gives pleasure to them. If a behavior results in an unpleasant or unsatisfactory sensation the probability of that behavior decreases. Therefore, this theory suggested that mental disorders may be the consequence of dysfunctional behaviors that produce a pleasant feeling. Hence, the treatment for them was to unlearn them through behavioral modification.
There are few shortcomings to psychotherapy. The use of verbal therapy may not be helpful for all patients suffering from a mental illness. Also, in some cases the therapy shifted the blame away from one’s moral character towards early childhood experience and hence stigmatizing the notion that mental illness could be overcome by willpower alone. Freud himself stated that the “deficiencies in our [the psychoanalytic] description would probably vanish if we were already in a position to replace the psychological terms by physiological or chemical ones”. Now neuroscience has come to a point where this goal seems possible.
Biological Approaches to Mental Illness
Biological approaches treat mental illness by affecting the biological processes that produce the symptoms. The biological diagnosis of mental illness started in the beginning of the twentieth century and eventually lead to biological treatments. Before 1910, Paul Ehrlich demonstrated a drug that kills the virus T. pallidum that can cause a brain infection. This infection could result to general paresis of the insane, a disorder that progresses from mania to cognitive deterioration and finally to paralysis and death. When penicillin was discovered in 1928 by Alexander Fleming it was found to be a more effective treatment that ultimately almost eliminated the disorder altogether.
The biological causes of mental disorders are difficult to determine and therefore often remain a mystery. Diagnosis on the basis of symptoms is sometimes misleading because several different causes may have similar effects on patients. Additionally, illnesses have both genetic and environmental causes. The complexity of brain disorders makes their treatment difficult, but the development of neuroscience offers practices to resolve these issues. Both the psychosocial and biological approaches have a sound neurobiological basis for the treatment of mental illness.
Affective Disorders: Major Depression
We chose major depression out of the mental illnesses mentioned in chapter 22 because it is a common, sometimes invisible illness. However, its mechanisms are complicated much like the function of the brain itself and it has far more effect on our cognitive functions than what one might assume.
Its main symptoms are a lowered mood and decreased interest in activities. For diagnosis, the symptoms must have been present every day for at least two weeks. Additionally, major depression can cause insomnia, fatigue, diminished ability to focus on tasks and thoughts about death or possibly suicidal ideation. Depressive episodes will not last longer that 2 years on average unless they have progressed to the point that their occurrence is chronic. Another form of depression, dysthymia, occurs more rarely in comparison to the major depression, but in almost all cases specified treatment is needed to correct the imbalances in the brain.
Biological Bases of Affective Disorders
The Monoamine Hypothesis
Neuroscientific observations have proven that mood in general is related to the levels of norepinephrine and serotonin in the brain. According to the monoamine hypothesis, depression results from a deficit of diffuse modulatory systems of these monoamine neurotransmitters. Modern antidepressants are based on this discovery by inhibiting the reuptake of these neurotransmitters in the synaptic cleft. By inhibition, the activity of serotonin and norepinephrine is increased, which affects the mood. However, the effects of antidepressants may take weeks to develop, the regulation of mood is more complicated and monoamine hypothesis alone cannot explain it.
The Diathesis–Stress Hypothesis
Scientific evidence indicates that mood disorders, such as depression, are affected by genes which run in families. Therefore, some people have a greater tendency to have depression. This phenomenon is called diathesis. Additionally, stress causing factors, e.g., abuse or neglect in childhood are significant risk factors to having depression in adulthood.
According to the diathesis-stress hypothesis, the main site of depression and other affective disorders is the hypothalamic-pituitary-adrenal (HPA) axis, which in general is responsible for regulating the segregation of the hormone cortisol in response to stress. Its humoral activity is regulated by the hypothalamus, hippocampus, and amygdala. In depressed patients, the feedback controlled by hippocampus is disturbed. Therefore, instead of an inhibiting signal, which would be received in normal HPA function, the loop receives an activating signal. This leads to the hyperactivity of HPA.
Anterior Cingulate Cortex Dysfunction
Brain studies have found that anterior cingulate cortex is more active at a resting state with people who have depression. The activity in this cortex is linked to regions of the hippocampus, amygdala, hypothalamus, brain stem and prefrontal cortex. It has been indicated that the activity in the ACC is increased when a person recalls a sad or other negative memory.
This week’s lecture included a lot of interesting information about mental illnesses that affect many people. We were looking forward to learning about the biological mechanisms of depression. The neuroscience concerning mental illness is developing quickly and it is exciting to follow as new studies about treatments are put out.