Cortical activity time-locked to the shift and maintenance of spatial attention

Abstract

Attention increases the gain of visual neurons, which improves visual performance. How
attention is controlled, however, remains unknown.  Clear correlations between attention and
saccade planning indicate that the control of attention is mediated through mechanisms
housed in the oculomotor network. Here, we used event-related fMRI to compare overt and
covert attention shifts. Subjects covertly or overtly shifted attention based on an endogenous
cue, and maintained attention throughout a long and variable delay. To insure continued
attention, subjects counted when the attended target dimmed at near-threshold contrast
levels. Overt and covert tasks used identical stimuli and required identical motor responses.
Additionally, a staircase procedure that adjusted the target-dimming contrast separately for
covert and overt trials equated the difficulty between conditions and across subjects. We
found that the same regions along the precentral and intraparietal sulci were active during
shifts of covert and overt attention.  We also found sustained activation in the hemisphere
contralateral to the attended visual field.  We conclude that maps of prioritized locations are
represented in areas classically associated with oculomotor control.  The read-out of these
spatial maps by posterior visual areas directs spatial attention just as the read-out by
downstream saccade generators directs saccades.

From: Ikkai, A. & Curtis, C. E. (2008). Cortical activity time-locked to the shift and maintenance of spatial attention. Cerebral Cortex. 18:1384-1394.

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