We read this paper with great interest. We considered of particular interest the results showing preservation of cortical thickness in specific regions that play a role as hubs of the salience and default mode networks in "superagers", in comparison with older adults with typical age-related expected decline in cognition.
As physical activity is a well know protective factor against cognitive decline, it would...
We read this paper with great interest. We considered of particular interest the results showing preservation of cortical thickness in specific regions that play a role as hubs of the salience and default mode networks in "superagers", in comparison with older adults with typical age-related expected decline in cognition.
As physical activity is a well know protective factor against cognitive decline, it would be interesting to know if any measure of aerobic fitness or exercise index (current or past) are at disposal to examine possible differences between those groups. We believe this would be particularly important considering our recently published data showing metabolic changes measured with FDG-PET in areas that correspond to hubs of both networks in subjects with mild cognitive impairment (MCI) after 24 weeks of aerobic training (Porto et al., 2015). Surprisingly, the areas with more important metabolic changes were the rostral anterior cingulate cortex (ACC) (decrease in resting-state metabolism) and the retrosplenial cortex (increase in resting-state metabolism). Also, physical activity decreased the intensity of the precuneus metabolic impairment in the MCI group in relation to a control group after the aerobic training. We hypothesized an increase in efficacy in the salience network induced by physical training (reflected by its decreased metabolism at rest) may influence the default mode network due to better regulation of brain networks, increasing the metabolism at rest in the precuneus, an important node of this network.
A volumetric increase in the rostral ACC was already shown after an aerobic training program in cognitively normal older adults (Colcombe et al., 2006). Interestingly, while studying the acute effects of aerobic exercise in rest brain glucose metabolism in normal young adults, other authors found a generalized metabolic decrease in all investigated areas, particularly in the dorsal ACC (Kemppainen et al., 2005). When participants were split into two groups ("trained" versus "less trained"), the trained group had a noticeable reduction in the dorsal ACC when compared to the less trained group, suggesting some type of long-term adaptive metabolic changes in the region. This is concordant with our findings. As others studies of "superagers" have been showing preservation of the ACC (Harrison et al., 2012; Rogalski et al., 2012; Gefen et al., 2015), this node of the salience network may have an important role in the relationship between physical fitness and cognitive preservation.
It is possible that neuroplasticity induced by long-term physical exercise may also influence the thickness of the cortex in "superagers", as there is an anatomical concordance between brain regions that changed after our (and others) aerobic program and those preserved in older adults with youthful memory. There might be an important link between both studies, eventually suggesting potential mechanisms between global health and the "superagers" cortical signature.
A suggestion for future studies is to take into account measures of past and current physical fitness when comparing cognition, brain structure and function in different groups of older subjects, once it is possible that better fitness is related to healthier brain aging.
References:
Colcombe SJ, Erickson KI, Scalf PE, Kim JS, Prakash R, McAuley E, Elavsky S, Marquez DX, Hu L, Kramer AF (2006) Aerobic exercise training increases brain volume in aging humans. J Gerontol A Biol Sci Med Sci 61:1166-1170.
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Harrison TM, Weintraub S, Mesulam MM, Rogalski E (2012) Superior memory and higher cortical volumes in unusually successful cognitive aging. J Int Neuropsychol Soc 18:1081-1085.
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Rogalski EJ, Gefen T, Shi J, Samimi M, Bigio E, Weintraub S, Geula C, Mesulam MM (2012) Youthful Memory Capacity in Old Brains: Anatomic and Genetic Clues from the Northwestern SuperAging Project. J Cognitive Neurosci 25:29-36.
Sun FW, Stepanovic MR, Andreano J, Barrett LF, Touroutoglou A, Dickerson BC (2016) Youthful Brains in Older Adults: Preserved Neuroanatomy in the Default Mode and Salience Networks Contributes to Youthful Memory in Superaging. J Neurosci 36:9659-9668.
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