Beneficial Effects of Foreign Language Learning and Aerobic Exercise on Dentate Gyrus Volume and Mnemonic Discrimination in Healthy Older Adults: Results from a Randomized Controlled Trial.

Protecting hippocampal structures, such as the cornu ammonis 3 and dentate gyrus (CA3/DG), that are tied to mnemonic discrimination could be a promising approach to mitigate the age-related decline in episodic memory. This study examines the potential benefits of cognitive and physical engagement, specifically language learning and moderate aerobic exercise, for maintaining hippocampal subfield integrity and memory performance. In a randomized controlled trial involving 142 healthy older adults (aged 63-78 years), we investigated the effects of a 6-month regime comprising language learning, aerobic exercise, and their combination. Participants were assigned to one of four groups: an active control, language-only, exercise-only, or combined language and exercise group. CA3/DG volume remained stable in the language-only and combined groups, while the non-language groups showed a significantly greater decrease in volume, suggesting that foreign language learning may protect against normal aging-related CA3/DG volume loss. Comparatively, the exercise-only and combined groups showed significant improvements in mnemonic discrimination performance, while the non-exercise groups did not, indicating that aerobic exercise can improve this aspect of memory in older adults. Notably, the combined group was the only group to exhibit both preserved CA3/DG volume and improved mnemonic discrimination. No evidence for a boosting effect of the combined intervention on either outcome was observed. This suggests that, while the effects of language learning and aerobic exercise may be independent at the level of measured outcomes, they provide complementary benefits when combined. Finally, the initial volume of the subiculum was found to predict changes in mnemonic discrimination performance across all groups, indicating that this region may play a potential role in episodic memory changes over time. Contrary to our expectations, changes in hippocampal subfields were not directly associated with changes in mnemonic discrimination. In conclusion, this study highlights the potentially separate roles of foreign language learning and aerobic exercise in enhancing aspects of episodic memory in older adults; future research may address whether their combination may yield broader functional benefits than either intervention alone.