Abstract
Atrophy of the medial temporal lobe (MTL) occurs with aging, resulting in impaired episodic memory. Aerobic fitness is positively correlated with total hippocampal volume, a heavily studied memory-critical region within the MTL. However, research on associations between sedentary behavior and MTL subregion integrity is limited. Here we explore associations between thickness of the MTL and its subregions (namely CA1, CA23DG, fusiform gyrus, subiculum, parahippocampal, perirhinal and entorhinal cortex,), physical activity, and sedentary behavior. We assessed 35 non-demented middle-aged and older adults (25 women, 10 men; 45–75 years) using the International Physical Activity Questionnaire for older adults, which quantifies physical activity levels in MET-equivalent units and asks about the average number of hours spent sitting per day. All participants had high resolution MRI scans performed on a Siemens Allegra 3T MRI scanner, which allows for detailed investigation of the MTL. Controlling for age, total MTL thickness correlated inversely with hours of sitting/day (r = -0.37, p = 0.03). In MTL subregion analysis, parahippocampal (r = -0.45, p = 0.007), entorhinal (r = -0.33, p = 0.05) cortical and subiculum (r = -0.36, p = .04) thicknesses correlated inversely with hours of sitting/day. No significant correlations were observed between physical activity levels and MTL thickness. Though preliminary, our results suggest that more sedentary non-demented individuals have less MTL thickness. Future studies should include longitudinal analyses and explore mechanisms, as well as the efficacy of decreasing sedentary behaviors to reverse this association.
Highlights
Growing evidence from clinical trials, epidemiological and neuroscience research suggests that physical exercise is a promising intervention for delaying the onset of dementia and Alzheimer’s disease [1,2,3,4]
Several mechanisms have been postulated for how physical activity improves brain health [24,25], including increased blood flow in the brain to promote the development of new neurons [26] and delaying brain structural and functional decline; in contrast, only few studies [27] have looked at sedentary behavior from a mechanistic perspective
The whole brain voxel-based structural analyses found no regions of significant differences by physical activity levels or time spent sitting. In this neuroimaging study examining relationships between self-reported sedentary behavior, physical activity and thickness of medial temporal lobe (MTL), we found that sedentary behavior, but not physical activity, was associated with less thickness in the MTL and its subregions
Summary
Growing evidence from clinical trials, epidemiological and neuroscience research suggests that physical exercise is a promising intervention for delaying the onset of dementia and Alzheimer’s disease [1,2,3,4]. Several mechanisms have been postulated for how physical activity improves brain health [24,25], including increased blood flow in the brain to promote the development of new neurons [26] and delaying brain structural and functional decline; in contrast, only few studies [27] have looked at sedentary behavior from a mechanistic perspective. It has been suggested that sedentary behavior may have deleterious effects on glycemic control, and the increased glycemic variability and resultant decreased cerebral blood flow may lead to worse brain health [27] In this preliminary analysis, we explore associations between physical activity levels, sedentary behavior and thickness in MTL and neighboring cortical sub-region structures in nondemented middle-aged and older adults, examining the relationship of physical activity and time spent sitting simultaneously on brain thickness. We hypothesized that both lower levels of physical activity and time spent sitting will be associated with less thickness in MTL and its subregions
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