Changes in conditioned postural responses. Comparison between cerebellar patients and healthy subjects

Postural responses elicited by external perturbation change characteristically during classical conditioning. This is assumed to be controlled by the cerebellum. In this study conditioning of postural responses in cerebellar patients was compared with that of healthy subjects. Subjects were tested when standing on a platform. Perturbations consisted of platform tilts (unconditioned stimulus, US), preceded by an auditory signal (conditioned stimulus, CS). The recording session consisted of US-alone and paired CS-US trials. In healthy subjects, unconditioned response (UR) amplitude decayed significantly with time in the recording session, especially strongly during paired trials. Amplitudes of cerebellar patients, however, decayed modestly and continuously, independently of the presence (paired trials) or otherwise of a CS. In addition, only healthy subjects established conditioned responses. Our data suggest that the prior auditory information is used to prepare postural responses. Deficits in cerebellar patients suggest a possible role of the cerebellum in controlling this plastic motor-related process.