Hippocampal volume as mediator between physical fitness and cognitive performance in old age – preliminary results

Abstract

AbstractBackgroundPrevious studies show that physical activity counteracts age‐related memory decline and is positively associated with hippocampal volume. However, only few studies examined if hippocampal volumes mediate the effect of physical activity on cognitive performance. Furthermore, exercise modalities other than aerobic activity are rarely considered in this context. Since sarcopenia (muscle atrophy) is associated with age‐related cognitive decline, muscular capacity seems to be another essential fitness indicator.MethodForty‐one cognitively unimpaired older adults (age: 72.94 ± 7.85yrs; 24 female) underwent a comprehensive neuropsychological test battery assessing, i.a., global cognitive performance using CERAD‐Plus (Consortium to Establish a Registry for Alzheimer’s Disease) and PACC5 (preclinical Alzheimer’s cognitive composite). Their physical fitness was measured in the form of both aerobic (VO2max) and muscular capacity (z‐normalized composite: grip strength, appendicular skeletal muscle mass and walking performance). Anterior (aHCV), posterior and whole hippocampal volumes (wHCV) were extracted from their T1w MRI images (3T MEMPRAGE, 0.8×0.8×0.8mm resolution) using the T1‐ASHS segmentation algorithm (manual correction of 32 hemispheres). Total gray matter volumes (GMV) were extracted using CAT12 in SPM12. Mediation analyses were performed to test the hypothesis that GMV or hippocampal volumes (corrected for intracranial volumes) mediate the positive effect of physical fitness on cognitive performance including age, sex and education years as covariates (bootstrapping approach: 10000 iterations).ResultHigher aerobic capacity (VO2max) was related to better cognitive performance (CERAD, p = .048), as was higher muscular capacity (CERAD, p = .002; PACC5, p = .002). Higher muscular capacity, but not VO2max, further predicted aHCV (p = .021) and wHCV (p = .035). Only wHCV mediated the relationship between muscular capacity and global cognitive performance (PACC5, p = .045).ConclusionOur results provide further evidence that higher aerobic and muscular capacity are associated with better global cognitive performance in older adults. While preliminary, the results suggest that muscular capacity exerts its neuroprotective effects at least partially via greater structural integrity of the hippocampus. The absence of a mediation effect of GMV may support the specific importance of maintained hippocampal structural integrity against cognitive decline. However, our small sample size may limit the statistical power to detect effects.