Saccade-related activity in the lateral intraparietal area. I. Temporal properties; comparison with area 7a

Abstract

1. The cortex of the inferior parietal lobule (IPL) contains neurons whose activity is related to saccadic eye movements. The exact role of the IPL in relation to saccades remains, however, unclear. In this and the companion paper, we approach this problem by quantifying many of the spatial and temporal parameters of the saccade-related (S) activity. These parameters have hitherto been largely unstudied. 2. The activity of single neurons was recorded from Macaca mulatta monkeys while they were performing a delayed-saccade task. The analysis presented here is based on 161 neurons recorded from the lateral intraparietal area (LIP), a recently defined subdivision of the IPL; and 54 neurons recorded from the neighboring part of the IPL, area 7a. Overall, 409 IPL neurons were isolated in this study. 3. The typical activity of IPL neurons during the delayed-saccade task has three basic phases: light sensitive (LS), memory (M), and S. These basic phases are common to neurons of both areas LIP and 7a. In each phase (LS, M, and S), individual neurons may or may not be active. Most LIP neurons, however, are active in more than one phase. 4. To compare the activity levels of different neurons, the actual firing rate was weighted by each neuron's background level, yielding an "activity index" for each neuron, in each phase of the task. We calculated the activity index for the LS and M phases and for three phases related to the saccade: a presaccadic (Pre-S), a saccade-coincident (S-Co), and a postsaccadic (Post-S) phase. For area LIP neurons the median values of the activity index were high for the LS, M, Pre-S, and S-Co activities, and slightly lower in the Post-S period. In area 7a the median values were low for the LS phase and, in particular, for the M and Pre-S phases, somewhat higher coincident with the saccade, and high post-saccadically. 5. In area LIP, in each phase, 49-63% of the neurons had excitatory activity, and 10-17% had inhibitory responses. 6. In contrast, in area 7a excitatory responses were most frequent in the Post-S phase (56%). Excitation was particularly infrequent during M (28%) and Pre-S (22%). The incidence of inhibitory responses varied too (4-18%). The time course of inhibition was roughly opposite that of excitation; the highest frequency of inhibitory responses occurred during the saccade.(ABSTRACT TRUNCATED AT 400 WORDS)

Integration of Visuospatial and Effector Information during Symbolically Cued Limb Movements in Monkey Lateral Intraparietal Area

“…Figure 1b shows population activity on the memory saccade task with saccades directed toward the RF center (thick trace) and toward the other locations tested during the search task (thin traces). These responses unambiguously identify our neurons as belonging to the LIP, because in no other parietal area can one find this strength and prevalence of delay and presaccadic activity (Barash et al, 1991;Murata et al, 2000;Snyder et al, 2000a).…”

Multimodal Representation of Space in the Posterior Parietal Cortex and Its Use in Planning Movements

“…Although adjacent to LIP, area 7a does not appear to play a direct role in saccades (Barash et al 1991a), and unlike LIP, which has relatively smaller and contralateral visual receptive fields (Blatt et al 1990), area 7a has large, bilateral fields (Motter & Mountcastle 1981).…”

Remapping for visual stability

“…Since this discovery many other brain areas have been shown to have neurons that remap, including the FEFs [32] and the SC [33,34]. These three brain areas are all strongly interconnected [29,31,[35][36][37] and contain neural signals related to both visual stimuli and saccadic eye movements [38][39][40][41].…”