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Abstract:
Using event-related fMRI methods, we have dissociated neural
activity related to top-down attentional control mechanisms from
the resultant modulation of perceptual processing in visual cortex.
Six healthy adult subjects (ages 22-34) participated in a
trial-by-trial spatial cueing study. BOLD fMRI data were analyzed
with SPM97, which allowed the hemodynamic responses to
attention-directing cues and targets to be separately modeled. The
cues produced bilateral inferior parietal cortex activations, with
the left parietal region being differentially activated as a
function of the direction of attention. In addition, the cues
produced activations in extrastriate regions contralateral to the
direction of attention, and this occurred prior to the onset of the
subsequent target stimuli. These extrastriate regions overlapped
with those selectively modulated by attention when the target was
presented. The attention-related modulation of target processing
was observed in the hemisphere contralateral to the attended
hemifield in the lingual and posterior fusiform gyri. The targets,
however, did not evoke activations in inferior parietal cortex.
These data support a model wherein the parietal cortex is engaged
during attentional orienting as part of a cortical network for top-
down attentional control over perceptual processing that
selectively modulates neuronal excitability in extrastriate visual
cortex.
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