The Compensatory Role of the Hippocampus in Working Memory Among Older Adults With Low MoCA Scores

Evidence suggests that working memory (WM) capacity decreases with age, resulting in cognitive decline. Given the link between aging and reduced hippocampal volume, this study examined whether and how hippocampal volume is associated with WM. 46 participants aged 65-85 years (Mage = 71.80, SD = 5.05, 17.4% male) took part in the study. WM was assessed with the Numbers Reversed test, cognitive functioning with the Montreal Cognitive Assessment (MoCA), and hippocampal structural data were obtained via magnetic resonance imaging. We hypothesized that hippocampal substructure volume would correlate with WM performance in older adults. Additionally, considering that the hippocampus interacts extensively with the fronto-parietal network, which is regarded as the core WM network, we hypothesized that this association would be stronger in adults with mild cognitive impairment (MCI), reflecting a compensatory role of the hippocampus. The results showed a statistically significant relationship between WM and hippocampus (r_s = 0.35, p < 0.05) and several hippocampal subsections in right and left hemispheres; however, the associations weakened after controlling for estimated total intracranial volume and MoCA scores in a regression model (R² = 0.113, F = 5.61, p = 0.022). At the group level, the MCI group exhibited stronger and more widespread associations between WM and hippocampal subregions than the cognitively intact group (R² values varying from 0.25 to 0.579, p ≤ 0.05). The results suggest that the hippocampus may play a more direct role in WM performance in older adults, particularly in the context of cognitive impairment, pointing to a possible compensatory mechanism and the involvement of long-term memory processes in WM.