Following numerous recent studies showing that aerobic exercise is good for maintaining memory, a group of neuroscientists set out to explore whether the opposite is also true: Does a sedentary lifestyle impair memory?
The Los Angeles-based researchers used MRI imaging to examine the brains of 35 healthy adults, aged 45 to 75, without cognitive problems or psychiatric disorders and took detailed lifestyle histories using a self-reported questionnaire.
Though the investigation is limited by its small size, the results, now published in PLOS ONE, show that brain volume in the region associated with fact and event-based memory is lower in older individuals who spend more hours per week sitting – suggesting that the lack of activity may cause this region to waste away over time.
After adjusting for differences that may be caused by age, sex, body mass index, and education level, a statistical analysis of the datasets revealed a trend toward a negative linear relationship between thickness in the medial temporal lobe (MTL) and the number of sedentary hours. This means that although there were exceptions to the pattern, the overall graph of brain volume vs hours spent sitting is a downward sloping line.
When assessing individual areas within the MTL, the authors found the association between volume and sedentary behavior was strongest for the parahippocampal cortex, a section known to mediate memory creation and retrieval related to recognizing one’s surroundings.
Contrary to the authors’ expectations, there was no association between increased MTL volume and the average number of hours of physical exercise that participants did each week. Thus, they speculate that “sedentary behavior is a more significant predictor of brain structure, specifically MTL thickness, and that physical activity, even at higher levels, is not sufficient to offset the harmful effects of sitting for extended periods of time.”
As with other non-interventional control studies, the findings represent correlations between lifestyle factors and health outcomes and can’t definitively say that one causes the other – meaning we shouldn’t immediately jump to conclusions and reprimand anyone who doesn’t use a standing desk or pace nervously all day.
The authors concede that “time spent sitting” is a vague quantification of sedentary behavior that does not take into account habits that could affect cognitive decline.
“It is possible that there may be two distinct groups: mentally active sitting and mentally inactive sitting,” they wrote. “In mentally active sitting, individuals may be attending to cognitively demanding tasks such as crossword puzzles, documentation, writing, or computer games. In mentally inactive sitting, individuals may be engaging in less demanding, passive tasks such as watching television or movies.”
Another caveat: Since the participants weren’t followed over time, it’s impossible to determine whether or not their current MTL volumes are the result of previous degeneration or simply represent their baseline brain size.