CONVERGENCE OF DIRECTIONAL VESTIBULAR AND NECK SIGNALS ON CEREBELLAR PURKINJE-CELLS

Convergence of spatially oriented vestibular and neck signals within t he cerebellar anterior vermis in decerebrate cats was studied by recor ding the simple spike discharge of Purkinje (P) cells during wobble ei ther of the whole animal (vestibular input) or of the body under a fix ed head (neck input) at 0.156 Hz, 5 degrees and 2.5 degrees, respectiv ely. Both clockwise (CW) and counterclockwise (CCW) rotations were per formed. Units that had equal response amplitudes to CW and CCW rotatio ns (narrowly tuned neurons) were described by a single vector (S-max), characterized by a gain, a direction and a temporal phase. Units with different response amplitudes to CW and CCW rotation (broadly tuned n eurons) were described by two vectors (S-max and S-min). In addition t o these bidirectional units, there were also unidirectional units whic h responded either to CW or CCW rotation; in these cases the gain of S -max equals that of S-min. On the whole, 77% and 63% of the P cells re spending to vestibular and neck stimulation, respectively, showed a b idirectional broadly tuned or unidirectional behavior. These response patterns were attributed to the convergence of signals with different spatial and temporal properties. About 50% of the P cells from which r ecordings were made responded to stimulation of both sensory systems. However, the gains of the S-max vectors of the neck responses were muc h greater than those of the vestibular responses, at least for small a mplitudes of rotation, and were positively correlated with them. Usual ly the differences in the orientation components of the neck and vesti bular S-max vectors were larger, while the differences in temporal pha ses were smaller than 90 degrees. These findings suggest that periodic changes in the phase difference and gain ratio of the neck to the ves tibular response may occur during dynamic displacement of the head ove r the body, depending on the stimulus direction. As a result of these data, the P cells of the cerebellar vermis are expected to show promin ent responses to head rotation, which could affect the spatially organ ized postural responses by utilizing vestibular and reticular targets.