Environmental Influences on Cognitive and Brain Plasticity During Aging

Neurogenesis occurs in the dentate gyrus of the hippocampus throughout the life of a rodent, but the function of these new neurons and the mechanisms that regulate their birth are unknown. Here we show that significantly more new neurons exist in the dentate gyrus of mice exposed to an enriched environment compared with littermates housed in standard cages. We also show, using unbiased stereology, that the enriched mice have a larger hippocampal granule cell layer and 15 per cent more granule cell neurons in the dentate gyrus.

A model of the effects of aging on brain activity during cognitive performance is introduced. The model is called HAROLD (hemispheric asymmetry reduction in older adults), and it states that, under similar circumstances, prefrontal activity during cognitive performances tends to be less lateralized in older adults than in younger adults. The model is supported by functional neuroimaging and other evidence in the domains of episodic memory, semantic memory, working memory, perception, and inhibitory control. Age-related hemispheric asymmetry reductions may have a compensatory function or they may reflect a dedifferentiation process. They may have a cognitive or neural origin, and they may reflect regional or network mechanisms. The HAROLD model is a cognitive neuroscience model that integrates ideas and findings from psychology and neuroscience of aging.