Separating contributions of prefrontal cortex subregions to age-related associative memory impairments

Abstract

The anterior prefrontal cortex (aPFC) is believed to play a critical role in integrating the outputs of lower-order processes, such as evaluations of item or inter-item properties. The high-order integration functions attributed to the aPFC have been shown to support complex reasoning. but the region’s role in episodic encoding is less well understood. Emerging data suggest high-order PFC functions may be particularly susceptible to the effects of age and may contribute to older adults’ associative memory impairments. It is currently unknown how aging interferes with aPFC operations necessary for integrating multiple relations for episodic encoding and retrieval. We investigated this issue in the current fMRI study. Young and older adults were presented with an occupation and an object and were asked to judge how likely the two were to interact, either in general or within the context of a given scene. When provided with a scene, participants needed to consider and integrate the distinct relations between the three items to reach a decision: a task dependent on aPFC functions. fMRI data were collected during encoding, and memory for object-occupation pairings and their associated contexts was tested outside of the scanner. fMRI results showed greater left DLPFC activity with increasing integration demands for both young and older adults. Older adults exhibited memory impairments for both the pairs and contexts, despite similar engagement of aPFC regions as the young. This could indicate that integration processes were intact yet inefficient in older adults. Alternatively, performance deficits may have resulted from age-related differences in whole-brain patterns of task-related encoding activity.