Proprioceptive neck influences modify the information about tilt direction coded by the cerebellar anterior vermis

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Abstract
Objective To verify whether the direction of head tilt coded by the population response of Purkinje (P) cells located in the cerebellar anterior vermis is modified by the relative position of the body with respect to the head. Material and Methods In decerebrate cats, the responses of P cells to wobble of the whole animal were analyzed in order to compute the response vectors of the same cells to the labyrinthine input. These response vectors were used to evaluate the population response (vector) of all the recorded neurons to head tilt in specific directions. Results When the head was aligned with the body, the direction of the population vector closely corresponded to that of head tilt. A 30° body-to-head rotation to the left or right around a C1–C2 vertical axis modified the response vectors of most of the recorded neurons, leading to reciprocal deviations of the population vector from the direction of head tilt of ≈30°. Conclusion We propose that information from neck receptors regulates the convergence of labyrinthine signals with different spatial and temporal properties on corticocerebellar units, thus allowing the P-cell population to code the direction of body tilt.