The neuroanatomy of inhibitory control in healthy aging: Evidence from event-related fMRI

Working memory is an important cognitive function for selecting, maintaining, and manipulating relevant information and thoughts. Inhibitory control, or the ability to suppress irrelevant or interfering stimuli, is a crucial component of working memory. Impaired inhibitory control has been proposed to account for decreased efficiency in cognitive processing for older adults, particularly in working memory tasks. Previous imaging studies with older adults, although limited in number and scope, suggest that activation in older adults is more bilateral and more diffuse compared to younger adults. Three theories have been proposed to account for activation differences between younger and older adults: Recruitment, Reorganization, and Sigmoid Function. Thus, event-related fMRI was used with a response inhibition task to test these three theories and to expand on previous findings on inhibition in aging by examining successful and unsuccessful inhibition trials. Both younger and older adults were expected to exhibit primarily right prefrontal and parietal activation during inhibition, based on some preliminary studies. In addition, because older adults have exhibited greater activation compared to younger adults during successful inhibition in the left inferior frontal gyrus, left inferior parietal lobule and bilateral dorsomedial thalamic nuclei, similar findings were expected in the current study. There were eleven young adults and thirteen healthy older adults as participants in the current study. Contrary to expectations, older adults were not impaired in inhibitory performance when compared to younger adults, likely due to poorer than expected performance by younger adults. Cerebral activation during successful inhibition was predominantly in bilateral prefrontal and right parietal regions for older adults, but not in left parietal or bilateral thalamic areas. Unexpectedly, activation in younger adults was of greater relative magnitude compared to older adults in bilateral prefrontal areas, including the anterior cingulate. In addition, the bilateral frontal activation for younger adults was evident at the easiest level of the task. The present results best support the Recruitment theory. Finally, older adults exhibited greater activation for unsuccessful inhibition in several limbic, visual, and motor association areas, while younger adults did not, supporting the utility of using event-related fMRI in separating behavioral events within imaging studies