Stress Linked to Increased Risk of Dementia

Chronic stress has become not only a #1 health risk , but also a major way of life for too many of us. If you are honest with yourself, the risk of dementia is more frightening than a heart attack. We can survive a heart attack but once dementia sets in, there is no escape – to date. The important link for all us neuroscientists is how anxiety, fear, and stress affect the brain. Adding to the burgeoning research that has been done on how stress can damage the brain, Dr. Linda Mah and her Colleagues at the Rotman Research Institute at Baycrest Health Sciences in Canada recently published a review article in the journal, Current Opinion in Psychiatry (2016, 29, p 56-63). The article reasoned that stress exacerbates mental illnesses such as depression but also appears to increase the risk of dementia; this suggests a common mechanism for the development of dementia and stress-induced depression.

Chronic stress was defined as a “pathological state caused by prolonged activation of the normal acute physiological stress response.” Once the stress response becomes chronic, damage to the brain occurs by altering the neurocircuitry of fear: enhancing amygdalar functioning,while causing structural degeneration in the prefrontal cortex (PFC), the orbitofrontal cortex, and the hippocampus. This circuit ends by inhibiting PFC/hippocampus control over the stress response.

The hippocampus plays an important role in memory but it also plays a role in the regulation of emotions during a fear experience. Long-term exposure to cortisol and other stress hormones can cause the hippocampus to atrophy. The fear and anxiety neurocircuitry engages when the amygdala detects a threat and generates emotions, such as fear and anxiety. Then the medial prefrontal cortex and hippocampus work to downregulate the amygdala. Emotional regulation is achieved when the amygdala is balanced with the activity of the mPFC and hippocampus. A simplification is that fear and stress can cause the amygdala to become overactive and cause the PFC to become underactive. The end result is an increase in fear and anxiety (stress) and a decrease in the “thinking areas” of the brain that regulate the emotional response. In sum, “pathological anxiety and chronic stress are associated with structural degeneration and poor functioning of the hippocampus and the PFC, which Dr. Mah’s team believes may account for the increased risk of developing neuropsychiatric disorders, including depression and dementia.

While that is definitely sobering, there are some major positive comments to consider. For one thing, we know ways to control “chronic stress” such as mindfulness and exercise. For another, the damage to the hippocampus and the PFC may not be entirely irreversible. Antidepressant treatment and exercise both show promise in repairing the hippocampus. Sleep and power naps are effective in regenerating the PFC. Nonetheless, this brings us back to the most important point: Nothing changes until you do. Just knowing a fix exists doesn’t help unless you use it.

 

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