Figure 1.

Experimental design. A, The schedule of the experiment. In this example, a recording/stimulation electrode is located in the oculomotor region in the left caudate. In each experiment, the monkey performed three sessions of a visually guided saccade task: prestimulation control, stimulation after saccades, and follow-up test. Each session consisted of 100 trials in which the saccade target was presented randomly on the right or left. Only during the “stimulation after saccades” session was electrical stimulation applied to the caudate after saccades in a fixed direction (e.g., to the right or contraversive as shown in the top panel). In another experiment, the stimulation was applied after saccades to the other direction (e.g., to the left or ipsiversive as shown in the bottom panel). In each panel, the schematic horizontal eye position is shown, upward indicating rightward (or contraversive) and downward indicating leftward (or ipsiversive). B, Time events. After the animal fixated on the central fixation point for 1200 ms, a target appeared either in the right or left to which the monkey made a saccade. On a stimulation trial, after the monkey fixated on the target for 100 ms, electrical stimulation was applied for either 400 or 800 ms (current, up to 50 μA; pulse duration, 0.5 ms; frequency, 100 Hz). A liquid reward (0.1 ml) was given twice per trial: 500 ms after fixation onset and 200 ms after the end of the stimulation. On a nonstimulation trial, the animal kept fixating on the target for the same period of time as stimulation period (i.e., 400 or 800 ms plus 100 ms) to obtain the same amount of reward.