FIG. 1.

Temporal representation of effects of stimulation of the omnipause neuron (OPN) region on head-unrestrained gaze shifts. Horizontal amplitude (left) and velocity (right) are plotted as a function of time for rightward gaze shifts directed to a target that was briefly flashed at a 60° eccentricity in tangential coordinates. Several, individual control trials are shown in cyan and stimulation trials are shown in red. A, 1–3: effect of stimulation delivered prior to the onset of gaze shifts. Panels plot the gaze, head, and eye-in-head components of coordinated eye-head movements. The trials are aligned on target onset. For the 5 stimulation trials shown here, stimulation onset occurred 150 ms after target onset and lasted for 300 ms. B, 1–3: effect of stimulation triggered on the onset of gaze shifts. Panels plot the gaze, head, and eye-in-head components, each aligned on gaze onset, as a function of time. Stimulation was triggered as either gaze or head position left its computer controlled window around the fixation point. Stimulation duration for the illustrated red trials was 250 ms. Datasets shown in A and B have the same target configuration and were collected from the same stimulation site in 1 animal. →, reacceleration of head movements that accompany gaze shifts after stimulation offset. Also note that the gaze and eye velocity traces illustrated in this figure do not show the dual-peak modulation reported previously (Freedman and Sparks 2000). We speculate that this effect is most robust during visually guided movements. The movements illustrated here were performed in the memory-guided task, and the absence of visual information is shown to reduce peak velocity, at least of head-restrained saccades (Edelman and Goldberg 2003 excitatory postsynaptic potential). A preliminary examination of the appropriate data collected in the gap task was comparable to the modulation in movement kinematics (data not shown).