Spatially tuned auditory responses in area LIP of macaques performing delayed memory saccades to acoustic targets

Abstract

1. The lateral intraparietal area (area LIP) of the macaque's posterior parietal cortex (PPC) lies in the dorsal stream of extrastriate visual areas. It receives extensive visual inputs and sends outputs to several eye movement centers. It contains neurons with visual and saccade-related responses suggesting a role of area LIP in programming saccadic eye movements to visual targets. Because primates can also orient to nonvisual stimuli, we investigated whether LIP neurons process stimuli of other modalities besides the visual one by comparing their activity in auditory and visual saccade tasks. 2. We recorded the activity of single neurons of Macaca mulatta monkeys while they performed memory saccades to acoustic and visual targets. We analyzed the activity during stimulus presentation (stimulus period, S) and during the delay (memory period, M) between stimulus presentation and the saccade to its remembered location. 3. Among 80 area LIP neurons tested, we found 44 that had S period and/or M period responses following presentation of the auditory stimulus. Most of these responses were spatially tuned, i.e., selective for the left or right stimulus location (27 of 29 S responses; 25 of 29 M responses). 4. The majority of neurons with responses in the auditory memory saccade task also responded in the visual version of the task. Eighty-nine percent (24/27) were clearly bimodal in the S period, and 88% (23/26) were bimodal in the M period. 5. Almost all the neurons with spatially tuned auditory responses that were bimodal were also spatially tuned in their visual responses (20/22 for S responses; 18/19 for M responses). The spatial tuning for the two modalities was the same in 85% (17/20) of the tested neurons for the S responses, and in 83% (15/18) of the tested neurons for the M responses. 6. Area LIP contains a population of neurons that respond to both visual and auditory stimuli. This result is consistent with our finding that the memory activity of many LIP cells encodes the next planned saccade. If cells are coding planned movements, they should be active independently of the sensory modality of the target for the movement, as was the case for most of the neurons described in the present study.