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Milena Raffi, Ralph M. Siegel; Optical recordings reveal a functional architecture for spatial attention in the posterior parietal cortex of the behaving macaque. Journal of Vision 2002;2(7):441. doi: 10.1167/2.7.441.
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The influence of spatial attention in the parietal cortex was evaluated using optical imaging of intrinsic signals at 605nm. The most dorsal aspects of area 7a and dorsal prelunate (DP) were imaged. Recordings were made in the right hemisphere of a macaque trained to fixate a 0.1° red dot and perform a cued detection task. Two 10° expanding optic flow stimuli were simultaneously presented 10° to the left and right (or above and below) the target. The monkey responded to a change in the structure of one of the two stimuli. A 2° white cue instructed the monkey as to which stimulus would change. A behavioral catch-trial control was also used for which the cue was incorrect. Behaviorally, there was a decrease in the reaction time of 25–50 msec when the monkey was correctly vs. incorrectly cued indicating a spatial attentional shift. The evoked optical response across the posterior parietal cortex depended on the locus of attention with the appearance of columns corresponding to the location of the attentional cue. We quantified these effects using a linear regression analysis. The columns were seen in all the experiments performed over 10 months and had the same dimension in both horizontal and vertical paradigm. These attentional columns were not seen in controls when just the cue was presented and the animal attended only to the central fixation point. For verification, multi-unit recordings were made using both the attentional task and the control task. The great majority of neurons showed no dependence at the onset of the stimuli upon the cue condition. A control paradigm in which the animal had to detect a central fixation point dimming showed that the cue alone had little or no effect on the firing rate. Thus the observed columns are not likely to result from the cue stimuli, but rather the spatial focus of the attention. The columns represent a novel functional architecture correlated with attention.
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