Well-known environmentally generated brain dysfunctions include the following:
- Fetal alcohol syndrome: Fetal alcohol syndrome develops when the mother drinks excessive alcohol during pregnancy. Alcohol crosses the placental barrier and can damage neurons and brain structures leading to cognitive and functional disabilities such as attention and memory deficits, impulsive behavior, and stunted overall growth. Fetal alcohol exposure is a significant cause of intellectual disability, estimated to occur in about 1 per 1,000 live births. It is associated with distinctive facial features, including a short nose, thin upper lip, and skin folds at the corner of the eyes.
- Maternal stress: If a mother is highly or chronically stressed while pregnant, her child is more likely to have emotional or cognitive problems, such as attention deficits, hyperactivity, anxiety, and language delay. The fetal environment can be altered when maternal stress changes the mother's hormone profile. It is thought that this occurs through the hypothalamic-pituitary-adrenal axis via the secretion of cortisol, a stress hormone that has deleterious effects on the developing nervous system. More recently, it has been shown that epigenetic changes in DNA expression can affect germ cells and, therefore, be inherited.
- Post-traumatic stress syndrome (PTSD): PTSD is a severe anxiety disorder that develops after psychological trauma, such as the threat of death, as in war, or a significant threat to one's physical, sexual, or psychological integrity that overwhelms the ability to cope, as in sexual assault. Traumatic events cause an overactive adrenaline response, which persists after the event, making an individual hyper-responsive to future fearful situations.
PTSD is characterized by cortisol dysregulation and high catecholamine secretion characteristic of the classical fight-or-flight response. These hormones divert resources from homeostatic mechanisms, such as digestion and immune responses, toward those needed for immediate, intense muscular exertion. Extreme or chronic stress can eventually damage the brain as well as the body.
Some evidence shows that desensitization therapies, in which the PTSD sufferer re-experiences aspects of the stressor in a controlled environment, can mitigate some of its effects. Such therapy, if successful, may be superior to generic anti-anxiety medication that may deal only with the symptoms, rather than the cause of the disorder.
