COMPENSATION FOR GAZE PERTURBATION DURING INACTIVATION OF THE CAUDAL FASTIGIAL NUCLEUS IN THE HEAD-UNRESTRAINED CAT

Muscimol injection in the caudal part of the fastigial nucleus (cFN) l eads, in the head-unrestrained cat, to a characteristic dysmetria of s accadic gaze shifts toward visual targets. The goal of the current stu dy was to test whether this pharmacological cFN inactivation impaired the ability to compensate for unexpected perturbations in gaze positio n during the latency period of the saccadic response. Such perturbatio ns consisted of moving gaze away from the target by a transient electr ical microstimulation in the deep layers of the superior colliculus si multaneously with extinction of the visual target. After injection of muscimol in the cFN, targets located in the contralesional hemifield e licited gaze shifts that fell short of the target in both ''perturbed' ' and ''unperturbed'' trials. The amplitude of the compensatory contra versive gaze shifts in perturbed trials coincided with the predicted a mplitude of unperturbed responses starting from the same position. Tar gets located in the opposite hemifield elicited hypermetric gaze shift s in both trial types, and the error of compensatory responses was not statistically different from that of unperturbed gaze shifts. These r esults indicate that inactivation of the cFN does not interfere with t he ability of the head-unrestrained cat to compensate for ipsiversive or contraversive perturbations in gaze position. Thus the gaze-related feedback signals that are used to compute a reference signal of desir ed gaze displacement are not impaired by cFN inactivation.