Given the heated debate about whether men and women have brain differences that affect cognition, psychologists are searching for definitive answers. However, research in humans is confounded by factors such as diet, medication, lifestyles, rearing and culture. As a result, psychologists are studying non-human primates in controlled setting to get a clearer, less distorted picture.
New cross-sectional studies of Rhesus monkeys spotlight a gender gap in their spatial memory, but only in young adulthood and only with untrained females. The research appears in the February issue of Behavioral Neuroscience, which is published by the American Psychological Association (APA). Says lead author Agnès Lacreuse, PhD, of Emory University, “Rhesus monkeys are good models of human aging because they are similar to humans in terms of endocrine, cognitive and neural characteristics. In addition, they are useful in the study of possible sex differences in cognitive aging because they provide a model that is not confounded by sex differences in longevity or dementia.”
Lacreuse and her co-authors at The Yerkes National Primate Research Center (Emory University) and the Boston University School of Medicine tested spatial memory in 90 adult rhesus monkeys divided among three age groups: Young (less than 15 years old), middle aged (between 15 and 20), and old (20 or older). The monkeys played a sort of shell game, locating where food was hidden after they saw it covered in one of 18 identical covered wells on a tray.
Although young-adult males had better spatial memory than females, choosing the correct food location more often, they peaked early. The performance of the older groups revealed a sharp drop-off in performance. As a result, by old age, male and female monkeys had about the same performance.
A second study of 22 Rhesus monkeys showed that in young adulthood, simple spatial-memory training did not help males but dramatically helped females, raising their performance to the level of young-adult males and wiping out the gender gap. Training probably focused the females’ attention on the spatial features of the task, say the authors, whereas the males seem to have a natural tendency to attend to these features.
The authors say the results have important implications for understanding sex differences in spatial abilities across the life span. Given the impact of both age and training, cognitive ability is clearly not a static quantity. However, longitudinal studies are needed to follow animals over time and, notes Lacreuse, “to find potential causal relationships in each sex between age-related changes in certain factors, such as hormones, and age-related changes in cognition.”
She continues, “A few reports in humans suggest that men show greater age-related cognitive decline relative to women. Our results in monkeys are consistent with these reports, at least concerning the specific domain of spatial cognition.” Lacreuse and her co-authors speculate that declining testosterone might be the culprit because in aging men, declining spatial ability has been linked to a gradual decline in testosterone – perhaps because testosterone affects the hippocampus, a brain area associated with spatial ability.
Lacreuse adds that there the few studies on sex differences in cognitive aging in humans have been inconclusive. “Some of the inconsistencies may come from confounds and also the use of different tasks across studies,” she says. “It is important to note that in the rhesus monkey, we only find the sex difference in spatial memory, not other cognitive domains.”