Spatial and non-spatial attention effects in the activity of macaque posterior parietal cortex neurons

Abstract

Posterior parietal cortex (PPC) has long been implicated in the control of spatial attention. Recent studies have also suggested a role of PPC in other forms of attention, like attention to object features and task switching. We investigated this by recording single neurons from area 7a of one monkey engaged in spatial and non-spatial attention tasks. Non-spatial attention was explored by instructing the animal to discriminate either the color or the orientation of a small bar presented inside the neuron's receptive field (RF). To explore spatial attention, we compared responses to the same stimuli when the monkey discriminated their color or orientation vs. when attention was directed outside the RF. Firing rates were determined both in a visual response (V) epoch (120–320 ms after stimulus onset) and in a prestimulus (P) epoch (500 ms before stimulus onset). Out of 42 neurons, 34 in the V epoch and 23 in the P epoch showed a significant difference in activity depending on whether attention was allocated inside or outside the RF. Moreover, for 17 cells in the V epoch and 15 in the epoch, activity to identical targets depended on the stimulus feature the monkey was discriminating, revealing non-spatial attentional effects. Importantly, spatial and non-spatial effects often coexisted in the same neuron. Finally, in a new sample of neurons (n=33) we manipulated the order of presentation of color- and orientation-discrimination trials during the session. In the “repeat” condition, the monkey performed the same task for blocks of consecutive trials before switching, while in the “switch” condition the task varied randomly on a trial-by-trial basis. Preliminary data show that in both trial epochs 1/3 of the cells were significantly affected by the task in the “repeat” condition but virtually none in the “switch” condition. Together, the results suggest a role of PPC in multiple aspects of selective perception and selective perception-to-action coupling.