Cerebral Cortex Advance Access originally published online on October 5, 2007
Cerebral Cortex 2008 18(6):1384-1394; doi:10.1093/cercor/bhm171
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Cortical Activity Time Locked to the Shift and Maintenance of Spatial Attention
Department of Psychology and Center for Neural Science, New York University, 6 Washington Place, New York, NY 10003, USA
Address correspondence to Clayton E. Curtis, Department of Psychology and Center for Neural Science, New York University, 6 Washington Place, New York, NY 10003, USA. Email: clayton.curtis{at}nyu.edu
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 functional magnetic resonance imaging 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 readout of these spatial maps by posterior visual areas directs spatial attention just as the readout by downstream saccade generators directs saccades.
Key Words: attention • control • eye field • fMRI • saccade • salience • spatial