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Guillaume Dugué (ENS Paris)

Representation of self-generated head movements in the vestibulo-cerebellum

Head movements are primarily sensed in a reference frame tied to the head, yet they are used to calculate self-orientation relative to the world. This requires to re-encode head kinematic signals into a reference frame anchored to earth-bound landmarks such as gravity, through computations whose neuronal substrates remain to be determined. We studied the encoding of self-generated head movements in the caudal cerebellar vermis, an area essential for graviceptive functions, using a combination of multi-unit electrophysiological recordings and of recordings of head movements in freely moving rats. The firing of most caudal vermis Purkinje cells contained a fused representation of head gravitational acceleration and angular velocity. In a fraction of the cells, this representation was tuned in such a way that it reported how the head was rotating about an « external » axis, defined relative to the direction of gravity. These results suggest that the caudal cerebellar vermis might be involved in the calculation of head rotations in a gravitationally-polarized reference frame, a necessary step for coupling head rotations to vestibulo-postural control functions and for computing head direction in the horizontal plane.