A classic, common, neuroendocrine syndrome is the relationship between chronic stress, the hormone cortisol, the brain and its memory functions.
Some studies have looked at this by taking large groups of people and asking them to record how much stress they experience over time. These stressors could involve financial, occupational, marital and health related matters. Subjects also have their cortisol blood levels measured, their memory tested and the size of their hippocampi measured by brain MRI. The hippocampus is situated in the temporal lobes of the brain and is considered the “organ of short-term memory.”
These studies find wide variability in the amount of stress each member of the group reports. Some subjects experience low levels for a short time, while others experience high levels over a long time. The rest fall somewhere in between these extremes. Members in the highest-stress group tend to have the highest daily levels of cortisol in their bloodstreams. Members in the lowest-stress group tend to have the lowest daily levels of cortisol. When the members of these two extreme groups are compared on hippocampal size and memory scores, the high-stress/high cortisol group has smaller hippocampi and poorer memory scores than the low stress/low cortisol group. Importantly, other studies show that if the chronic stress ceases, cortisol levels decline, hippocampal size increases and memory scores improve.
Cortisol is a hormone that helps us deal with stress. Over the short term it actually sharpens memory functioning, presumably allowing us to better deal with the cause of the stress. However, longer-term exposure to high levels of cortisol hurts brain cells, especially those vulnerable cells in the hippocampus. This is thought to be caused by an overuse / overdrive situation. To protect themselves from burnout, the hippocampal cells seem to reduce their connections to each other so they are stimulated less. When done by millions of cells the whole hippocampus shrinks a little and functions a bit less. The MRI and the memory tests can see this.
The good news is if the chronic stress is reduced, this syndrome is reversible.