Cortisol is a hormone that helps a person respond to life’s challenges, essentially allowing humans to think on their feet and learn from their experiences. However, when stress is prolonged, going on for long periods of time, excessive cortisol is released and can actually impair memory as people age. A new study from the University of Iowa (UI), published in the Journal of Neurosicence this week, is the first to measure how cortisol affects the prefrontal cortex, which is the area of the brain that handles short-term memory.
The connections in the brain that help store, process and recall information are called synapses. As a person ages, long-term, repeated exposure to cortisol can cause the synapses to shrink and disappear. One of the study authors, Jason Radley, said that the hormone cortisol is believed to be responsible for “weathering” of the brain, using the analogy of a rock on a shoreline that eventually wears away with time and disappears. The negative consequences of excessive levels of cortisol can also include anxiety, digestion problems, high blood pressure and weight gain.
UI researchers used rats for their study, comparing 4-month-old rats to elderly rats. The rats were put in a T-shaped maze and given a treat when they remembered which way to run the maze. Depending on how long the rats had to wait to re-run the maze their memory declined, but the older rats with higher corticosterone (the equivalent of cortisol in a human) levels consistently performed worse than the others, choosing the right path only 58 percent of the time. The older rats with low levels of corticosterone were accurate 80 percent of the time.
When researchers examined tissue samples from the rats’ brains they found that the poorer performing animals had 20 percent fewer synapses than the others, indicating memory loss. However, older rats with low corticosterone levels ran the maze nearly as well as the younger rats and showed little memory loss. According to Radley and Rachel Anderson, lead author of the paper, short-term memory impairment connected with higher cortisol levels due to prolonged stress start at about age 65 in humans, which is about equivalent to the 21-month-old rats that were used in the study.
There is a difference between prolonged and acute pressure. Acute stress helps manage short-term incidents, such as a car accident. During periods of traumatic events cortisol increases the brain’s ability to function during stressful incidents, and can actually improve the learning process. However, when stress is long-term and cortisol levels are consistently high, the ability to recall memories can be impaired.
Results of the study are preliminary, but researchers say that memory impairment in aging is affected by the hormones produced during chronic stress. The Mayo Clinic recommends reducing the effects by identifying and reducing situations that trigger tension. Exercising, eating a healthy diet and getting enough sleep can all help a person stay sharper longer.
By Beth A. Balen