Cardiorespiratory fitness, memory and brain structures: cross-sectional study in eldery humans
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It is well established that physical exercise and cardiovascular fitness are beneficial for brain health. Cardiovascular fitness can attenuate both the neurobiological and cognitive consequences of age-related declines. Epidemiological studies provided converging evidence that exercise has a positive effect on mental health in individuals suffering from neurological disorders, and can reduce the risk for developing Mild Cognitive Impairment (MCI) and Alzheimer’s disease (AD). Although there is a large amount of evidence from animal research suggesting a relationship between aerobic exercise and medial temporal lobe neuroplasticity, the majority of human literature that studied the effect of exercise on cognition have focused on executive control, attention networks along with other prefrontal and posterior parietal -mediated cognitive functions, but not on hippocampus mediated memory function. In a cross-sectional study using established behavioral tasks known to recruit the hippocampus and entorhinal cortex (EC) and structural MRI in healthy older adults, we tested the hypothesis that (1) aerobic fitness levels are positively associated with hippocampus dependent memory task performance. (2) aerobic fitness levels are positively associated with the structure of the hippocampus and EC. (3) the volume of hippocampus and thickness of EC are associated with behavioral tasks performance. In addition, we examined the relationship of aerobic fitness with brain regions known to show cortical thinning that predict AD dementia. Healthy older adult (age 55-85 years) underwent a standard graded submaximal treadmill test to determine cardio-respiratory fitness (Modified-Balke protocol, VO2max). Freesurfer MRI analytic software was used to calculate cortical thickness and volume of T1-weighted MR images. Greater aerobic fitness was associated with greater volumes in the left and right hippocampus before controlling for multiple comparisons but not with EC thickness. Aerobic fitness did not correlate with behavioral task performance. Furthermore, there was a significant negative correlation between fitness level and right supramarginal gyrus, a brain area known to show cortical thinning in AD. Our results indicate that higher fitness level is positively associated with hippocampal volume and may be protective against loss of hippocampal volume with aging. These data extend prior work on the cerebral effects of aerobic exercise and fitness to the medial temporal lobe in healthy older adults thus providing compelling evidence for a relationship between aerobic fitness and structure of the medial temporal lobe memory system. Future studies are needed to examine causal relationships between these variables.