AUDITORY AND VISUAL-ATTENTION ASSESSED WITH PET

Brain mechanisms involved in the maintenance of attention to auditory and visual stimuli at different spatial locations were assessed using positron emission tomography with [O-15]water to measure regional cere bral blood flow (rCBF) changes in 13 normal volunteers. Simultaneous a uditory [dichotically presented consonant-vowel-consonants (CVCs)] and visual stimuli (vertically oriented, CVCs presented to the left and r ight of fixation) were presented on every trial. In different conditio ns subjects attended for targets in a specified stimulus channel (left or right ears or left or right visual fields) while maintaining fixat ion on a central x. Attending left or right for auditory stimuli incre ased rCBF in primary auditory cortex in Heschl's gyrus and in temporal lobe auditory association cortices in both hemispheres. Attending lef t or right for visual stimuli did not change rCBF in primary visual co rtex, and only attention to the right significantly increased rCBF in contralateral occipital cortex. Visual attention caused significant rC BF changes in a widespread network that included frontal, parietal, an d temporal cortical regions as well as the cerebellum, whereas rCBF ch anges due to auditory attention were largely localized in the temporal lobes. The results suggest that spatially directed attention is media ted by different mechanisms in the auditory and visual modalities. (C) 1997 Wiley-Liss, Inc.