The development of Alzheimer’s disease, as we know, has been linked to certain genetic markers. However, as scientists have come to learn more and more about the brain, they have been of the opinion that genetics alone rarely dictates the course of an illness. Rather, the interaction that occurs between a person’s genes and his environment is responsible for determining the nature and course of a disease. In this regard, a set of recent studies has discovered that stress is an important environmental correlate for Alzheimer’s disease.

Stress is already known to negatively impact a person’s psychological condition, which involves effects such as depression and anxiety. The finding that stressful conditions might be associated with neurodegenerative diseases, however, is relatively new.

Research on environmental factors involved in the development of the Alzheimer’s disease began when researchers noted that some twins did not develop the disease when they were expected to. Twin studies showed that when one twin had developed the disease, the other twin developed the disease only 40 percent of the time. Thus it was concluded that there must be other factors involved, too, since, if genes alone led to the development of the disease, then every twin must share the disease when the other twin had developed it. But clearly this was not the case.

Studies suggested that although stress alone does not degrade memory, it does seem to push animals at risk over the edge, making them less able to learn and remember new things. Stress may also hasten the onset of Parkinson’s disease, a neurodegenerative disorder characterized by motor difficulties, namely impaired motor coordination, tremor and rigidity. Parkinson’s symptoms result due to loss of brain cells that produces dopamine, which is a neuro transmitter essential for voluntary movement. In an experiment, a team of researchers found that a group of rats, which had been given corticosterone shots in brain areas comprising dopaminergic neurons elevating their stress hormones and then further exposed to experimentally produced stress, showed poor performance on motor tasks. They concluded that stress hinders the ability of dopamine cells to function normally which might either triggering or aggravating Parkinson’s symptoms.

This article is based upon the Scientific American publication, MIND.