Motor Dynamics Encoding in Cat Cerebellar Flocculus Middle Zone During Optokinetic Eye Movements

Departments of 1 Physiology, 2 Neurosurgery, and 3 Otolaryngology, Yamanashi Medical University, Tamaho, Yamanashi 409-3898, Japan Kitama, Toshihiro, Tomohiro Omata, Akihito Mizukoshi, Takehiko Ueno, and Yu Sato. Motor Dynamics Encoding in Cat Cerebellar Flocculus Middle Zone During Optokinetic Eye Movements. J. Neurophysiol. 82: 2235-2248, 1999. We investigated the relationship between eye movement and simple-spike (SS) frequency of Purkinje cells in the cerebellar flocculus middle zone during the optokinetic response (OKR) in alert cats. The OKR was elicited by a sequence of a constant-speed visual pattern movement in one direction for 1 s and then in the opposite direction for 1 s. Quick-phase-free trials were selected. Sixty-six cells had direction-selective complex spike (CS) activity that was modulated during horizontal (preferring contraversive) but not vertical stimuli. The SS activity was modulated during horizontal OKR, preferring ipsiversive stimuli. Forty-one cells had well-modulated activity and were suitable for the regression model. In these cells, an inverse dynamics approach was applied, and the time course of the SS rate was reconstructed, with mean coefficient of determination 0.76, by a linear weighted superposition of the eye acceleration (mean coefficient, 0.056 spikes/s per deg/s 2 ), velocity (5.10 spikes/s per deg/s), position ( 2.40 spikes/s per deg), and constant (mean 34.3 spikes/s) terms, using a time delay (mean 11 ms) from the unit response to the eye response. The velocity and acceleration terms contributed to the increase in the reconstructed SS rates during ipsilateral movements, whereas the position term contributed during contralateral movements. The standard regression coefficient analyses revealed that the contribution of the velocity term (mean coefficient 0.81) was predominant over the acceleration (0.03) and position ( 0.17) terms. Forward selection analysis revealed three cell types: Velocity-Position-Acceleration type ( n = 27): velocity, position, and acceleration terms are significant ( P