Difference between visually and electrically evoked gaze saccades disclosed by altering the head moment of inertia

Difference between visually and electrically evoked gaze saccades disclosed by altering the head moment of inertia. J. Neurophysiol. 83: 1103-1107, 20 00. Differences between gaze shifts evoked by collicular electrical stimula tion and those triggered by the presentation of a visual stimulus were stud ied in head-free cats by increasing the head moment of inertia. This maneuv er modified the dynamics of these two types of gaze shifts by slowing down head movements, Such an increase in the head moment of inertia did not affe ct the metrics of visually evoked gaze saccades because their duration was precisely adjusted to compensate for these changes in movement dynamics. In contrast, the duration of electrically evoked gaze shifts remained constan t irrespective of the head moment of inertia, and:therefore their amplitude was significantly reduced. These results suggest that visually and electri cally evoked gaze saccades are controlled by different mechanisms. Whereas the accuracy of visually evoked saccades is Likely to be assured by on-line feedback information, the absence of duration adjustment in electrically e voked gaze shifts suggests that feedback information necessary to maintain their metrics is not accessible or is corrupted during collicular stimulati on. This is of great importance when these two types of movements are compa red-to infer the role of the superior colliculus in the control of orientin g gaze shifts.