Both aerobic exercise and strength training have been shown to improve memory in older women with likely mild cognitive impairment (MCI). Now a research team has looked into how exercise in older adults with MCI impacts brain structure.
Previous research has shown that physical exercise has a positive impact on cognitive performance in older adults. One study showed that after 12 months of walking three times a day, healthy community-dwelling older adults showed an increase in the size of their hippocampus, compared to a shrinking hippocampus in the control group. (The hippocampus is of particular interest to researchers due to its importance for learning and memory.) However, it was unclear whether exercise would have a similar effect for older adults who were already experiencing mild cognitive decline.
MCI is a greater-than-expected decline of cognitive abilities, but one that does not significantly interfere with an individual’s everyday functioning. However, having MCI does significantly increase the risk of developing Alzheimer’s. Every year, 10 to 30 percent of older adults with MCI develop Alzheimer’s, compared to one to two percent of older adults without MCI. If exercise continues to positively impact the brains of adults with MCI, perhaps an exercise-based intervention could alter the trajectory of cognitive decline and the loss of functional independence in these individuals.
A recent study involved 86 women aged 70 to 80 with probable MCI. These women were randomly assigned to three exercise conditions: aerobic exercise, strength training, and a control group that focused on balance and muscle tone training. Of these women, between 8 and 11 in each group were given MRIs before and after the 12-week exercise programs, which met twice a week. The aerobic program consisted of walking at a pace that would provide aerobic benefit; the strength program included free weights and strength training exercise machines; and the balance and stretching group did stretching exercises, balance exercises, and relaxation techniques. This group served as a useful control, because it eliminated the potential impact of effects of the social interaction in these programs and of potential physical benefits of traveling to the training centers.
The researchers had previously reported that the aerobic group had significantly improved balance, physical mobility, and cardiovascular function compared to the control group. They also found that there was no statistically significant difference in program participation between the three groups, with the average percentage of sessions attended ranging from 54 to 60 percent of all sessions.
When the researchers looked for changes in hippocampus volume six months after the pre-program scans, the aerobic group was found to have significantly larger hippocampus volumes than the control group, on both sides of the brain. The total increase in hippocampus volume was 4 percent, which was a larger increase than was seen for aerobic exercise in an earlier study of older adults without MCI. This may be due to only having women in the MCI study, since women had previously been shown to enjoy greater cognitive benefits from aerobic training than men. The strength training group did not show a significant difference in hippocampus volume compared to the control group. Both the strength and control groups showed a shrinkage in the hippocampus, which is consistent with expected hippocampus shrinkage over time in this age group.
However, the study’s findings on the relationship between increased hippocampus size and performance on cognitive tests provided confusing results. The entire aerobic group, including those who did not receive MRIs, showed greater improvement than the control group in a task of recalling a group of words after being interrupted by being presented a different set of words. However, when researchers looked at how the increase in hippocampus volume related to the performance on these tasks, they found that increased hippocampus size was associated with poorer performance on this task. The reasons for this surprising association remain unclear, and this finding will need to be investigated further. There remains much research still to be done on the relationship of changes in the brain and cognitive performance.
Yet in light of the improvement of the entire aerobic group on this cognitive task and the aerobic program’s impact on hippocampus size during a period of life where the hippocampus is generally shrinking, this study does provide additional evidence for the benefits of aerobic exercise on the brain and cognition.
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