Encoding of smooth-pursuit eye movement initiation by a population of vermal Purkinje cells.

Lesion studies suggest that the oculomotor vermis (OMV) is critical for the initiation of smooth-pursuit eye movements (SPEMs); yet, its specific role has remained elusive. In this study, we tested the hypothesis that vermal Purkinje cells (PCs) may be needed to fine-tune the kinematic description of SPEM initiation. Recording from identified PCs from the monkey OMV, we observed that SPEM-related PCs were characterized by a formidable diversity of response profiles with typically only modest reflection of eye movement kinematics. In contrast, the PC population discharge could be perfectly predicted based on a linear combination of eye acceleration, velocity, and position. This finding is in full accord with a role of the OMV in shaping eye movement kinematics. It, moreover, supports the notion that this shaping action is based on a population code, whose anatomic basis is the convergence of PCs on target neurons in the cerebellar nuclei.