Researchers linked elevated levels of a stress hormone to memory deficits later in life.
A recent study found aged rats that had elevated levels of the stress hormone corticosterone showed signs of structural changes in the brain as well as short-term memory deficits, a Society for Neuroscience news release reported.
Most people experience some extent of mental decline as they get older, but how rapidly this progresses varies from case to case. Researchers are looking into what causes some people to experience more severe or faster-developing mental decline.
Studies suggest the body's response to stress can speed up the processes. The stress hormone corticosterone (similar to cortisol) has been linked to structural and functional decline of the hippocampus in several animal studies.
The researchers measured the amount of stress in the blood of both young and old rats as well as looked at the cells in the prefrontal cortex (which is responsible for short-term memory).
The team found that older animals with high levels of corticosterone had fewer connections between the cells in the prefrontal cortex; in the younger mice the cell connections were similar regardless of hormone levels.
"Older animals with higher levels of stress hormones in their blood have 'older' frontal cortexes than animals with less stress hormones," Stanford University professor Robert Sapolsky, PhD, an expert on the damaging effects of long-term stress who was not involved with this study, said in the news release. "Thus, stress may act as a pacemaker of aging in this key brain region."
Older rats with higher stress levels had a 20 percent reduction in the density of the dendritic spines, which form connections between cells.
The team looked at how well rats of different ages and stress levels performed on a working memory test; older animals with higher hormone levels tended to make more mistakes.
"These findings are not meant to indicate that high stress hormones are the only factor in determining the decline of mental abilities during aging," Jason J. Radley of the University of Iowa, said in the news release. "Nonetheless, this study suggests that the effects of these stress hormones on the brain may be much more widespread than we previously thought."
