Researchers have found that long-term running as part of an exercise regime in middle age helps in wiring ‘old’ new neurons born in early adulthood, or adult-born neurons, into a network relevant to the maintenance of episodic memory encoding during aging. Episodic memory is a type of long-term memory involving conscious recollection of previous experiences together with their context in terms of time, place, and associated emotions. Published in the journal eNeuro, the researchers from Florida Atlantic University (FAU), US, and the Center for Research and Advanced Studies (CINVESTAV), Mexico, said the study provided novel insight into the benefits of exercise and that it should motivate adults to keep moving throughout their lifetime, especially during middle age.
Deficits in cognitive ability linked with aging are associated with reduced hippocampal volume. The hippocampus and adjacent cortices are brain areas essential for learning and memory. Aging-related memory function decline is also associated with the degradation of synaptic (junction between two neurons) inputs from the perirhinal and entorhinal cortex onto the hippocampus, brain areas that are essential for pattern separation, and contextual and spatial memory.
Along with significantly increasing these adult-born neurons, long-term running was found to enhance the recruitment of presynaptic (sub)-cortical cells to their network. That is, running not only rescued perirhinal connectivity but also increased and altered the contribution of the entorhinal cortices to the network of old adult-born neurons.
“Long-term exercise profoundly benefits the aging brain and may prevent aging-related memory function decline by increasing the survival and modifying the network of the adult-born neurons born during early adulthood, and thereby facilitating their participation in cognitive processes,” said Henriette van Praag, corresponding author, an associate professor of biomedical science in FAU.
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“Long-term running may enhance pattern separation ability, our ability to distinguish between highly similar events and stimuli, a behaviour closely linked to adult neurogenesis, which is among the first to display deficits indicative of age-related memory decline,” said Carmen Vivar, corresponding author, Department of Physiology, Biophysics and Neuroscience, Centro de Investigacion y de Estudios Avanzados del IPN in Mexico. “We show that running also substantially increases the back-projection from the dorsal subiculum onto old adult-born granule cells,” said van Praag. “This connectivity may provide navigation-associated information and mediate the long-term running-induced improvement in spatial memory function. Our study provides insight as to how chronic exercise, beginning in young adulthood and continuing throughout middle age, helps maintain memory function during aging, emphasising the relevance of including exercise in our daily lives,” said Vivar.
In this study, the researchers studied the effects of long-term running on a network of new hippocampal neurons generated in young adult mice, at middle age. More than six months after tagging of the adult-born neurons with a fluorescent reporter vector, they identified and quantified the direct afferent inputs to these adult-born neurons within the hippocampus and (sub)cortical areas, when the mice were middle-aged.