Spontaneous Gaze Shifts in Intact Head-free Rats and Following Inferior Olive and Cerebellar Lesions.

Abstract

Recent experiments have shown that after lesions of the inferior olive or of the flocculus and paraflocculus of the cerebellum, in the pigmented rat, spontaneous saccades made when the head is completely restrained are followed by a large postsaccadic drift. The aims of the present paper were to study (i) the strategies and the characteristics of spontaneous eye - head coordinated gaze shifts in intact pigmented rats and to compare them with those described in other mammals, (ii) how they are affected by inferior olive and flocculus - paraflocculus lesions, and (iii) whether in these groups of animals the stability of the gaze is more deficient when the head is free to rotate in the horizontal plane (head-free condition) relative to the head-fixed condition. Three types of gaze shift strategy of intact rats are described and characterized. Following inferior olive or flocculus - paraflocculus lesion the dynamic parameters of such gaze shifts (the main sequences of head, gaze and eye and the timing of eye and head movement onset) are not significantly affected. The main deficits of lesioned animals affect the stability of gaze at the end of gaze shifts. After inferior olive lesion the amplitude of the postsaccadic drift of the gaze is 43.2% of the gaze saccade in the head-fixed condition, which is reduced to 22.9% in the head-free condition. Following flocculus - paraflocculus lesion the postsaccadic drift of gaze is even more reduced than after inferior olive lesion, changing from 39.2% in the head-fixed condition to only 9.7% in the head-free condition.