Contribution of the cerebellar anterior vermis to the gain and spatiotemporal properties of the vestibulospinal reflexes: a behavioural and cellular analysis.

Abstract Functional inactivation of the lobules IV-V of the cerebellar vermis obtained by local microinjection of the GABA-A agonist muscimol, depresses, in decerebrate cats, the amplitude of the VS reflex recorded from the forelimb extensor TB and may occasionally affect its spatial and/or temporal properties. The activity changes induced by tilting the animal head in all the possible directions were uniformly reduced. Experiments of unit recording from the same region submitted in other experiments to the drug injection, revealed that a large proportion of P-cells (67%) showed spatially tuned responses to the labyrinth input, characterized by preferred directions which were uniformly scattered over the horizontal plane. Neurons with opposite orientations could be found within a relatively narrow volume of corticocerebellar tissue, that could have been easily inactivated by injected volumes (0.25 μl, 8 μg/μl) of muscimol. We proposed that the spatial tuning of the P-cell responses to the labyrinth input is a basic property which allows the cerebellum to control the gain of VS reflexes elicited by head tilts in a broad directional range.