Aging-related changes of neural mechanisms underlying visual-spatial working memory

Capacities of the prefrontal cortex (PFC) such as working memory (WM) are known to decline with increasing age. However, it is unclear which neurofunctional mechanisms may underlie this aging-related cognitive decline. The finding that PFC activity tends to be less lateralized in older subjects has led to the assumption of a hemispheric asymmetry reduction in the PFC associated with aging (HAROLD). Using functional magnetic resonance imaging (fMRI), we here investigated aging-related neurofunctional alterations during the performance of a visual-spatial WM task with differential levels of difficulty. Older volunteers activated dorsolateral PFC regions bilaterally while young subjects recruited these areas only in the left hemisphere. These data corroborate the hemispheric asymmetry reduction in the PFC associated with aging (HAROLD) account. However, we also observed functional reorganizations in parieto-occipital areas, and with increasing WM demands, an aging-related reversed hemispheric asymmetry of prefrontal activations. Importantly, neither PFC nor parieto-occipital reorganizations prevented older participants from showing worse WM performance than young volunteers. We conclude that frontal-parietal functional reorganizations may reflect compensational mechanisms related to aging, but do not obviate diminished visual-spatial WM performance in older people.