Neuronal Response To Reward And Luminance In Macaque LIP During Saccadic Choice

Recent work in decision neuroscience suggests that visual saliency can interact with reward-based choice,and the lateral intraparietal cortex(LIP)is implicated in this process.However,to the best of our knowledge,no studies have examined whether or how single LIP neurons integrate visual saliency and reward in a choice setting,and the neural mechanisms involved are unclear.Adding to the complexity of this question is the increasing evidence that the LIP is not a functionally homogeneous area.These results highlight the urgency for broader sampling when examining the contribution of the LIP to saccadic choice using single-unit recordings.In this context,we conducted this study to investigate how LIP encodes both reward and visual salience,and whether coding related neurons are evenly distributed in the LIP.To address these issues,we performed an unbiased sampling of LIP neurons covering its anterior-posterior(AP)extent while monkeys performed a two alternative choice task in which the reward and luminance associated with each offer were varied independently.We discovered that the animal’s choice was dictated by the reward amount while the luminance had a marginal effect.In the LIP,neuronal activity corresponded well with the animal’s choice pattern,in that a majority of reward-modulated neurons encoded the reward amount in the neuron’s preferred hemifield with a positive slope.In contrast,compared to their responses to low luminance,an approximately equal proportion of luminance-sensitive neurons responded to high luminance with increased or decreased activity,leading to a much weaker population-level response.Meanwhile,in the non-preferred hemifield,the strength of encoding for reward amount and luminance was positively correlated,suggesting the integration of these two factors in the LIP.Moreover,neurons encoding reward and luminance were homogeneously distributed along the anterior-posterior axis of the LIP.Overall,our study provides further evidence supporting the neural instantiation of a priority map in the LIP in reward-based decisions.