Age-related differences in cortical recruitment and suppression: implications for cognitive performance.

The discovery of a coherent set of cortical regions showing activation during rest and deactivation during task performance has reignited an old debate in the field of neuroscience, one that questions the reflexivity of the human brain and provides evidence towards a more intrinsic functional architecture. The default-mode network (DMN) comprising of such consistent cortical regions has become a topic of increasing interest in both healthy and diseased populations. In this study, using a well-examined version of the verbal n-back task, interleaved with periods of rest blocks, we investigated whether the deactivation of the cortical regions comprising the DMN moderates individual differences in behavioral performance in a group of older adults. We recruited 25 young and 25 older adults for our study and presented them with blocks of the n-back task, with varying levels of load, interleaved with periods of fixation. A direct comparison of the young and older participants revealed both a reduction in the up-regulation of the prefrontal and parietal regions in response to increasing task demands, along with a reduction in the down-regulation of DMN regions with increasing cognitive load in the elderly. Better performance in the young adults was associated with the capability to modulate the regions of the working memory network with increasing task difficulty, however enhanced performance in the older cohort was associated with greater load-induced deactivation of the posterior cingulate cortex. This study adds to the existing gamut of aging literature, providing evidence that DMN function is critical to cognitive functioning in older adults.