The effects of age on the neurocognitive architecture of verbal and spatial working memory.

This study addressed the effects of age and memory load on the neural substrates of verbal and spatial working memory. Using fMRI, 21 young adults and 23 seniors were scanned while performing verbal and spatial delayed-response tasks in which memory load was manipulated. The event-related design allowed for the separation of encoding-, maintenance-, and retrieval-related neural activity. While many neuroimaging studies have examined the effects of memory load, stimulus type, and age on the neural correlates of working memory individually, this experiment is unique in that no study has combined them in a single set of subjects. In young adults, analyses revealed regional load-sensitivity during verbal and spatial working memory. Regional load-sensitivity was observed during verbal maintenance and spatial retrieval, suggesting that the load manipulation affected verbal and spatial working memory at different stages of processing. Analyses also revealed that young adults and seniors activated strikingly similar neural networks during verbal and spatial working memory, suggesting the neurocognitive architecture of working memory remains stable across the lifespan. However, several important age-differences emerged during the maintenance interval. First, while verbal maintenance-related neural activity was largely left-lateralized in the two groups at the two lower memory loads, young adults also activated the right hemisphere extensively at the high verbal memory load, whereas seniors did not. This finding may represent the neural correlate of age-related declines in working memory capacity. Second, during verbal and spatial working memory, at a low memory load, while performance accuracy was age-equivalent, seniors activated right DLPFC more than young adults. However, at the high memory load, seniors were less accurate than young adults and also activated right DLPFC to a lesser degree than young adults. This suggests that at low levels of memory load, seniors can maintain performance in the face of age-related declines in the neural circuitry of working memory via the recruitment of DLPFC-mediated mechanisms. However, at high levels of memory load, these results suggest that have seniors have reached a capacity limitation at which DLPFC recruitment is not sufficient to maintain performance.PhDBiological SciencesCognitive psychologyNeurosciencesPsychobiologyPsychologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/126108/2/3237918.pd