Encoding of hindlimb kinematics by spinocerebellar circuitry

Earlier work from our laboratory showed that principal component waveforms (PCs) from an ensemble of DSCT movement responses correlated with either the waveform of the limb axis length or orientation trajectories, suggesting that DSCT circuitry might elaborate an explicit representation of limb endpoint kinematics independent from limb geometry. In this study, we tested this idea by decoupling limb geometry from endpoint position with mechanical constraints that blocked the motion of the knee joint during step-like movements applied passively to the hindlimb of anesthetized cats. Only about half of the 50 cells studied showed statistically different response patterns when the limb was constrained compared to the unconstrained condition (control). However, the PC waveforms extracted from responses that showed significant changes with the knee constrained were found to be identical to those extracted from control responses. Instead, the differences between constrained and control responses could be accounted for by changes in the weighting of PCs suggesting a modulation of global response components rather than an explicit representation of local parameters.