Stress and Depression

The stress response is important for survival and adaptation. The stress response, which involves both emotional and physiological changes, is an adaptive response that motivates our behavior so we can protect ourselves. It is turned on by the brain working in specific neural circuits modulated by neurotransmitters and hormones.

There are important individual differences in humans. Some people may have the ability to quickly shut down their emotional, behavioral, and hormonal responses to stressful situations, while others may have prolonged responses. Over time, these prolonged responses could affect physiology and brain function.

For example, increased release of cortisol over a long time could affect glucose regulation, bone density, immune function, and the function of specific brain cells. These individuals could become vulnerable to developing physical and mental diseases. Evidence suggests that overactivity of corticotropin-releasing factor, a brain neurochemical, may play a role in why some people become excessively anxious and depressed. About 50 percent of depressed patients have overactivity of the stress hormone response, which is regulated by corticotropin-releasing factor. Whether this overactivity causes or contributes to depression is unclear. It is also possible that overactivity of this system may play a role in altering the structure and function of certain brain cells.

Studies of childhood experiences may reveal a connection between stress hormone levels and depression. A study in 1945 by Spitz examined the psychological condition of orphans who were hospitalized and provided with a clean and healthy environment but with very little contact or comfort by the nurses. These children were described as withdrawn, and social interactions with them became increasingly difficult. In more recent studies, data suggests that children who have been deprived of contact or comfort develop alterations in their stress hormonal responses.

Studies of monkeys also can provide some insight into the relationship between stress hormones and depression. One long-ago experiment by Harlow focused on monkeys who were raised apart from their mothers with little or no physical contact with other animals. When these monkeys became mothers, they were either indifferent and withdrawn or violent and abusive to their offspring; they were unable to regulate their own emotions. This suggests that their early experience promoted the development of a vulnerability that proved to be very important when they became adults.

The offspring of these motherless mothers, moreover, began to exhibit similar abnormal behavior. The fact that some of the motherless monkeys were withdrawn and others were abusive reflects the differences among individuals who experience trauma. We can't give a complete answer as to why one individual responds in one way and another responds in a completely different manner. We're dealing with very complicated brain systems involving numerous brain chemicals interacting across many brain regions.

Scientists hope that by studying how the stress response system relates to development and depression they may be able to develop early recognition and new treatment strategies, perhaps targeting early environmental factors as well as the hormonal systems that may be affected.

Source: National Institute of Mental Health