CORTICAL SITES OF SUSTAINED AND DIVIDED ATTENTION IN NORMAL ELDERLY HUMANS

Human brain mechanisms subserving attention have been assigned to pref rontal, midfrontal, and posterior parietal cortices, as well as to the anterior cingulate and the thalamus. To map these mechanisms in the b rain, most studies have used selective attention tasks; few studies ha ve mapped the brain under sustained or divided attention. The present study was designed to create maps of regional activity associated with sustained and divided attention using two different sensory modalitie s: visual checkerboard stimulation and vibrotactile stimulation of the right hand, Five cerebral PE-tomograms of O-15-labeled water uptake w ere acquired from 16 elderly healthy subjects during sustained or divi ded attention to the frequency of stimulation. To locate active brain regions, the t-statistic map of relative changes in cerebral blood flo w was coregistered to the subjects' averaged brain MR images and to th e standard Talairach brain coordinate system. Attention was associated with activity in two sites, the right middle frontal gyrus (Brodmann area 46) and the right inferior parietal lobule (Brodmann area 40). Th e frontal site was more active when the subjects attended to the visua l stimulus and when the attention was divided, while the parietal site was more active during attention to the vibrotactile stimulus and dur ing simple sustained attention, Our observations are consistent with t he hypotheses (1) that the right posterior parietal attention center s ubserves attention to several sensory modalities and (2) that a cortic al network of specific neuronal sites subserves both sustained and div ided attention. These hypotheses must be tested in further studies. (C ) 1997 Academic Press.