The inhibitory surrounds of neurons in the lateral intraparietal area (LIP) of the monkey can be activated and modulated by top-down processes

Abstract

LIP represents a salience map composed of bottom-up visual, and top-down oculomotor and cognitive components. This salience map is considered to play a role in spatial attention and oculomotor processing. We have recently demonstrated that neurons in LIP have inhibitory surrounds: a maintained saccade plan to a stimulus presented outside the receptive field of a neuron can significantly suppress the visual activity evoked by a task-irrelevant distractor presented in the cell's receptive field during the delay period of the planned saccade (Falkner, Krishna, and Goldberg, SFN 2006). Here we show that this suppression can be modulated by purely cognitive, non-visual (top-down) processes in two distinct ways. First, the response to a distractor is reduced when the monkey plans a memory-guided saccade to the inhibitory surround, indicating that the saccade plan is sufficient to evoke suppression even in the absence of a visual saccade target. Second, when the monkey plans a saccade to the inhibitory surround, the suppression of the distractor response is strongly modulated by the expected reward following the completed saccade. We used the color of the saccade target to indicate the amount of reward to expect on that trial, and ascertained that the monkey learned the reward contingencies since he made shorter latency saccades to earn high rewards than he did to earn low rewards. In accordance with previous studies (Platt and Glimcher, 1999, Sugrue et al. 2004), we also find that signaling a higher reward evokes increased activity in neurons representing the saccade goal. Thus, the salience map in LIP, which determines the locus of attention at a given moment, is sharpened by cognitive factors that increase the activity of behaviorally relevant (highly rewarded) stimuli, and simultaneously suppress the neural response to competing objects in the surround.