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

Institute of Physiology, University of Munich, Germany.
Acta physiologica et pharmacologica Bulgarica 02/2001; 26(3):143-6.
Source: PubMed


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.

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    • "This integration and the scaling of gains appear to be mediated by the cerebellum (Dietz 1993). Indeed, cerebellumimpaired patients have difficulty scaling postural (Nashner 1976; Horak et al. 1989; Kolb et al. 2001) and stepping (Timmann and Horak 1998) responses according to context. The basal ganglia also appear to contribute to scaling of posture, as evidenced by poor postural responses in patients suffering from Parkinson's disease (Horak et al. 1992, 1996). "
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    ABSTRACT: The aim of the present study was to investigate the role of the human cerebellum in short-term (STH) and long-term habituation (LTH) of postural responses to repeated platform perturbations. Ten cerebellar patients and ten age- and sex-matched healthy controls participated. Twenty backward platform translations were applied on each of 5 consecutive days. Changes of postural response size within each day were assessed to determine STH and changes across days to determine LTH. Both controls and cerebellar patients showed a significant reduction of postural response size within each day (i.e. STH). No significant reduction of postural response size was observed across days (i.e. no LTH). Both controls and cerebellar patients, however, showed a tendency of response size to increase across days suggesting long-term sensitization. The amount of changes within and across days did not significantly differ between groups. The present findings suggest that changes of postural response size to repeated perturbations do not depend upon the integrity of the cerebellum.
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