Cerebellar control of saccade dynamics: contribution of the fastigial oculomotor region.
The fastigial oculomotor region is the output by which the medioposterior cerebellum influences the generation of saccades. Recent inactivation studies reported observations suggesting an involvement in their dynamics (velocity and duration). In this work, we tested this hypothesis in the head-restrained monkey with the electrical microstimulation technique. More specifically, we studied the influence of duration, frequency, and current on the saccades elicited by fastigial stimulation and starting from a central (straight ahead) position. The results show ipsilateral or contralateral saccades whose amplitude and dynamics depend on the stimulation parameters. The duration and amplitude of their horizontal component increase with the duration of stimulation up to a maximum amplitude. Varying the stimulation frequency mostly changes their latency and the peak velocity (for contralateral saccades). Current also influences the metrics and dynamics of saccades: the horizontal amplitude and peak velocity increase with the intensity, whereas the latency decreases. The changes in peak velocity and in latency observed in contralateral saccades are not correlated. Finally, we discovered that contralateral saccades can be evoked at sites eliciting ipsilateral saccades when the stimulation frequency is reduced. However, their onset is timed not with the onset but with the offset of stimulation. These results corroborate the hypothesis that the fastigial projections toward the pontomedullary reticular formation (PMRF) participate in steering the saccade, whereas the fastigiocollicular projections contribute to the bilateral control of visual fixation. We propose that the cerebellar influence on saccade generation involves recruiting neurons and controlling the size of the active population in the PMRF.
Institut de Neurosciences de la Timone, UMR 7289, Centre National de la Recherche Scientifique, Aix-Marseille Université, Marseille, France.
Julie
J
Quinet
Institut de Neurosciences de la Timone, UMR 7289, Centre National de la Recherche Scientifique, Aix-Marseille Université, Marseille, France laurent.goffart@univ-amu.fr.
Laurent
L
Goffart
D000818:Animals; D001703:Biophysics; D001931:Brain Mapping; D002529:Cerebellar Nuclei / Q000502:physiology*; D004558:Electric Stimulation; D007839:Functional Laterality / Q000502:physiology*; D008253:Macaca mulatta; D017711:Nonlinear Dynamics; D009801:Oculomotor Muscles / Q000294:innervation*; D011930:Reaction Time / Q000502:physiology; D012438:Saccades / Q000502:physiology*; D013997:Time Factors
brain stem; cerebellum; dynamics; primate; saccade