Mon, Jul 28, 2008 - Page 9 News List

Combating stress for a healthier, happier lifestyle

By Bruce McEwen

Stress contributes to the onset of cardiovascular disease and depression, among other illnesses. And it is not only major stressful life events that exact a toll on our bodies; the many conflicts and demands of daily life elevate and sometimes disrupt the workings of our response systems for stress, causing wear and tear on the body and brain.

This burden of chronic stress, called “allostatic overload,” reflects not only the impact of life experiences but also our genetic constitution. Moreover, individual habits such as diet, substance abuse, exercise and the quality and quantity of sleep also play a major role, as do early life experiences that set life-long patterns of behavior and physiological reactivity.

There are three categories of stress: positive stress, for which a person feels rewarded by surmounting a challenge; tolerable stress, which results from serious life events — for example, divorce, death of a loved one, loss of a job — but where the affected person has good support systems; and toxic stress, which involves the same types of serious events, as well as the accumulation of daily struggles, but without good support systems.

DEGREE OF CONTROL

The difference between tolerable and toxic stress depends on the perceived degree of control that a person experiences. Moreover, low self-esteem exacerbates a feeling of helplessness and lack of control. Social support by friends and family is vital to ameliorating the effects of tolerable stress and keeping it from becoming toxic.

These are all functions of the brain — the key organ in our response to stress. The brain interprets what is threatening and, therefore, stressful; regulates behavioral and physiological stress responses — the latter through the autonomic, immune and neuroendocrine systems; and is a target of stress, undergoing structural and functional remodeling of its circuits that affects its performance. This remodeling includes limited replacement of neurons in the hippocampus, a brain region important for spatial memory and memory of events in our daily lives.

The recognition of the brain’s vulnerability and plasticity under stress began with investigations of the hippocampus, and it now includes the amygdala, a brain region involved in fear, anxiety and mood, and the prefrontal cortex, which is important in decision making, memory, and top-down control of impulsive behavior, as well as regulation of the autonomic nervous system and stress hormone axis. Repeated stress causes neurons in the hippocampus and the prefrontal cortex to shrink and lose connections with other nerve cells, while it also causes neurons in the amygdala to grow and form new connections.

BOUNCING BACK

Because the remodeling of neurons by stress is reversible, researchers now believe that chronic anxiety disorders and depression represent a lack of resilience, or spontaneous recovery, in susceptible individuals.

Such a lack of recovery then requires medication, behavioral interventions, or both.

Hormones associated with stress protect the body and brain in the short run and promote adaptation, but the chronic activity of these hormones brings about changes in the body that cause allostatic overload, along with potential follow-on diseases.

For example, the immune system is enhanced by acute stress but suppressed by chronic stress. By the same token, the brain shows enhanced activity during acute stress, with improvement in certain types of memory, but undergoes structural changes that increase anxiety and decrease mental flexibility and memory capacity as a result of chronic stress.

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