Verbal and spatial working memory in older individuals: A positron emission tomography study.

Recent reviews of a substantial number of studies have partially resolved questions concerning the brain regions used by working memory for manipulation and representation. We report a large single experiment in middle-aged to older adults (n = 89), classified by hypertensive status. Our design addresses the question of regions related to manipulation and representation, most particularly comparing spatial and verbal working memory. A control, memory search, and 2-back running memory task were performed with identical stimuli and responses during whole-brain 15O water positron emission tomography (PET) scans. Letter or spatial position instructions created verbal or spatial working memory versions of the tasks. We assessed agreement with the literature using regions of interest that were defined by clusters of activation empirically derived from the literature by Wager and Smith (Wager, T.D. and Smith, E.E., Neuroimaging studies of working memory: a meta-analysis, Cognitive, Affective and Behavioral Neuroscience, 3 (2003) 255-274). Our results largely confirmed conclusions from the review on the organization of working memory into dorsal prefrontal manipulation and ventrolateral prefrontal maintenance areas and representation in dorsal and ventral paths. Specific verbal versus spatial comparisons were also concordant with prior work establishing posterior lateralized representation for different contents by working memory. The similarity of results between this older sample and results derived by others from younger participants is notable.