Chronic Stress and Memory Decline: A Classic Neuroendocrine Connection

Heads and Tales: The Neuroendocrine Blog of Alan R. Jacobs, MD
Alan Jacobs, MD, Neurology, 05:12PM Mar 23, 2010

A classic, not uncommon neuroendocrine syndrome is the relationship between chronic stress, the adrenal steroid hormone cortisol and both the size of the hippocampus and its memory functioning.

Some studies have looked at this, for example, by taking large groups of people and asking them to record how much stress they have experienced over time. These stressors could involve financial, occupational, marital and health related matters.
Subject also have their cortisol blood levels measured, their memory tested and the volume of their hippocampi measured by brain MRI. The hippocampus is part of the temporal lobes of the brain and is considered the "organ of short-term memory".

Studies like this find a range in the amount of stress each member of the group reports, with some experiencing low levels for a short time, others experiencing high levels over a long time, and the rest falling somewhere in between these extremes. And, members in the part of the group with the highest amounts of stress also have the highest amounts of cortisol in their bloodstreams, while members in the part of the group with the lowest amounts of stress have the lowest amounts of cortisol. If members of these two groups are compared on hippocampal size and memory scores, the high-stress/high cortisol group has smaller hippocampi and poorer memory scores and the low stress/ low cortisol group has larger hippocampi and better memory scores. Importantly, in studies such as -
Decrease in cortisol reverses human hippocampal atrophy following treatment of Cushing''s disease
Biological Psychiatry, Volume 46, Issue 12, Pages 1595-1602, M.Starkman et al - where the chronic stress goes away over time, then cortisol levels decline, the size of the hippocampus increases and memory scores improve back to normal.

Cortisol is a hormone that helps us deal with stress.
Over the short term it can actually sharpen memory functioning, presumably to allow us to better deal with the cause of the stress.
However, longer-term exposure to high levels of cortisol can hurt brain cells, especially those cells in the hippocampus.
This is thought to be caused by an overuse condition.
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 this syndrome is reversible if the chronic stress can be reduced.