Stress, Depression and Memory Loss
Research Reveals How Chronic Stress Impacts Brain Health
Managing stress and depression, even the tolerable, yet chronic manifestations that seem an unavoidable part of modern life, may be even more important to long-term brain health than once thought. Research from the last 20 years indicates that it may be the duration and not the severity of traumatic or depressive episodes that determines how much damage occurs or the body’s ability to recover from stressful events. Studies indicate that stress hormones kill or inhibit the growth of brain cells and adversely affect memory. The more prolonged the stress or depression, the more extensive the damage. Experiments also show that antidepressant medications and therapy may counteract and reverse the impact of stress by encouraging the growth of new cells.
The Role of the Hippocampus
Studies in the 1990s revealed that the hippocampus, the seahorse-shaped region of the brain that was once considered to be a storage spot for memories, actually gathers memories from incoming sensory experiences, and then assigns them to other parts of the cortex for long-term storage. In effect, the hippocampus’ job is to turn short-term memories into long-term ones. One of the ways the hippocampus sorts through all the sensory input it receives to determine what to do with it is through special receptors that interpret signals coming from outside the cells of the hippocampus. These receptors are how the hippocampus “hears” what’s going on around it.
When stress induces the release of hormones from the hypothalamus, the part of the brain that regulates instinctive behaviors, the receptors in the hippocampus pick them up and trigger a series of biochemical “fight-or-flight” responses. And while this ability to react to acute stress such as physical danger is critical to survival, recent evidence suggests that chemicals released in the stress response are responsible for damaging cells in the hippocampus, and that prolonged stress is much more harmful to the body than acute stress.
Joe Dispenza, author of Evolve Your Brain: The Science of Changing Your Mind, a 2007 book from Health Communications Inc. indicates that while acute stress is unavoidable, our bodies were not designed to withstand chronic emotional/psychological stress. Dispenza and other researchers believe that long periods of stress desensitize the body to stress hormones so that it requires higher and higher levels of biochemicals to initiate a response. He likens what occurs in the hippocampus-hypothalamus feedback loop in the presence of chronic stress to the cycle of addiction. Without recovery time between stressful events, the brain remains on high alert with the hypothalamus cranking out more and more hormones to alert an ever-shrinking hippocampus.
A Shrinking Hippocampus Affects Memory
The potential hazards of chronic stress on memory were discovered when neuroscientists studied the hippocampus in patients suffering from depression or who had been exposed to chronic stress or childhood trauma. The hippocampus is significantly smaller in these subjects. Scientists speculated the smaller hippocampus might be keeping depressed or stressed individuals from forming long-term memories. They found the longer the depression, stress or trauma continues, the more the hippocampus shrinks, and the more permanent the damage. Additionally, studies of depressed individuals showed that trauma that occurs before puberty predisposes the effected brain to stress-related illness for life.
Stress and Depression Management Can Rebuild the Hippocampus
Yet there is also evidence that neurogenesis (the birth of new brain cells) is very active in the hippocampus and that stress and depression management can mitigate the damage caused by stress hormones. Not only have animal studies shown that antidepressants increase the number of stem cells that become new brain cells in the hippocampus, but research into people who have recovered from depression, either through pharmaceutical or therapeutic intervention, indicates that memory improves, perhaps because the hippocampus has grown back. There is also increasing evidence that stress and antidepressant treatment stimulate gliogenesis (the birth of new glial cells which are the cells that provide energy, nutrition and more chemical receptors in support of the cells of the nervous system), thus indicating that monitoring stress and depression can improve long-term memory by revitalizing the hippocampus.
References:
Begley, Sharon. Train Your Mind, Change Your Brain: How a New Science Reveals Our Extraordinary Potential to Transform Ourselves. NY: Ballantine Books, 2007.
Doidge, Norman. The Brain That Changes Itself: Stories of Personal Triumph from the Frontiers of Brain Science. NY: Penguin Books, 2007.
Stress Blurs Memory
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