PREDICTION AND SET-DEPENDENT SCALING OF EARLY POSTURAL RESPONSES IN CEREBELLAR PATIENTS

We reported previously that patients with cerebellar deficits were una ble to scale the magnitude of their early automatic postural responses to the predicted amplitudes of surface translations based on central set from prior experience. The present study investigated whether this deficit in set-dependent amplitude scaling was based predominately on the cerebellar patient's disability (i) to predict perturbation ampli tudes on the basis of prior experience, (ii) to scale the gain or magn itude of upcoming postural responses or (iii) to habituate postural re sponses. The increase in size of the early postural response when a la rger than actual platform amplitude was expected and decrease when a s maller one was expected was defined as a measure of set-dependent ampl itude prediction. The suppression of the postural response when the sa me platform velocity was repeated was used as a measure of habituation . The correlation between the size of early postural responses and pla tform amplitudes when presented serially, but not randomly, tested the ability to scale the gain of postural responses based on prior experi ence. Results show that although cerebellar patients could predict per turbation amplitudes based on prior experience, they could not use thi s prediction to modify precisely the gain of responses. The ability to habituate the magnitude of postural responses was not affected by cer ebellar lesions. Thus, the cerebellum might not be critical for predic ting upcoming events or for habituating to repented postural stimuli, although it is important for accurate timing of response gain based on prediction.