EYE POSITION EFFECTS IN MONKEY CORTEX .2. PURSUIT-RELATED AND FIXATION-RELATED ACTIVITY IN POSTERIOR PARIETAL AREAS LIP AND 7A

We studied the effect of eye position on pursuit-related discharges an d activity during fixation in darkness for neurons of monkey visual co rtical areas (lateral intraparietal area) LIP and 7A. In a first step, neurons were tested for direction-specific activity related to pursui t eye movements while the monkey tracked a moving target. In consecuti ve trials the pursuit target moved in random order in one of four dire ctions on a translucent screen. For 39% of the neurons, located mostly in a dorsoposterior region of area LTP, as well as 42% of the neurons tested in area 7A, a direction-specific pursuit-rejected activity cou ld be found. To test whether responsiveness of these neurons was modul ated by eye position. we employed a pursuit paradigm. In this paradigm , the monkey had to track a target that started to move in the preferr ed direction with constant speed from five different locations on the screen in random order. For the majority of cells in both areas, pursu it-related activity was modulated by eye position. Most of the neurons tested also revealed an influence of eye position on their spontaneou s activity during fixation in darkness (fixation paradigm). For the ma jority of cells (>50%) recorded in both areas, two-dimensional regress ion planes could be approximated significantly (P < 0.05) or nearly si gnificantly (P < 0.1) to the neuronal discharges observed on the fixat ion paradigm and pursuit paradigm. For 79% of the LIP neurons and 83% of the 7A neurons tested In both experimental paradigms, the direction s of the gradients of the regression planes pointed into the same hemi field, suggesting a common neuronal mechanism mediating the eye positi on effect regardless of the behavioral task the monkey was performing. The observed effects very much resemble the effects of eye position o n light-sensitive and saccade-related responses already described for areas LIP and 7A. Regarding also our results observed for the middle t emporal and medial superior temporal areas, it is suggested that the o bserved modulatory effect of eye position on neuronal activity is a co mmon phenomenon in the macaque visual cortical system subserving an in ternal representation of the external space in a nonretinocentric fram e of reference.