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

ABSTRACT 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.

  • [Show abstract] [Hide abstract]
    ABSTRACT: Postural equilibrium is known to be controlled by sensorimotor reflexes and automatic control loops but also depends on high-level body representation in space, probably implicating the right temporoparietal cortex. Indeed, short-term prism adaptation to a 10 degrees rightward visual shift has been shown to reduce predominant postural imbalance in patients with right hemisphere damage, as it did for neglect symptoms. These effects are likely to be explained by a high level effect of prism adaptation on body and space representation, rather than by a sensorimotor effect. Cognitive after-effects of prism adaptation to a leftward visual shift, suggesting neglect-like symptoms, have also recently been shown in normal subjects on line bisection tasks. In the present study, we investigated the effect of wedge prism adaptation on postural control in normal subjects. Two groups of seven healthy subjects were either adapted to a leftward or a rightward visual shift. Results showed that our procedure induced changes in lateral postural control in normal subjects. Furthermore, this lateral postural after-effect was dependent on direction of prism adaptation. Indeed, only adaptation to a leftward visual shift induced significant rightward postural bias in normal subjects. The rightward postural lateral displacement was negatively correlated with the visual vertical. Both transfer and direction specific effect of visuo-manual adaptation to prisms on postural control suggest that effects of adaptation act more on high-level postural control linked to body representation in space or at least reveal close interaction between sensorimotor plasticity and body representation.
    Experimental Brain Research 02/2003; 148(2):219-26. DOI:10.1007/s00221-002-1294-3 · 2.17 Impact Factor
  • [Show abstract] [Hide abstract]
    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.
    Gait & Posture 03/2004; 19(1):16-23. DOI:10.1016/S0966-6362(03)00006-7 · 2.30 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The aim of the current study was to compare postural responses to repetitive platform-evoked perturbations in cerebellar patients with those of healthy subjects using a classical conditioning paradigm. The perturbations consisted of tilting of the platform (unconditioned stimulus: US) at random time intervals, preceded by an auditory signal that represented the conditioning stimulus (CS). Physiological reactions were recorded biomechanically by measuring the vertical ground forces, yielding the center of vertical pressure (CVP), and electrophysiologically by EMG measurements of the main muscle groups of both legs. The recording session consisted of a control section with US-alone trials, a testing section with paired stimuli and a brief final section with US-alone trials. Healthy control subjects were divided into those establishing conditioned responses (CR) in all muscles tested (strategy I) and those with CR in the gastrocnemius muscles only (strategy II), suggesting an associative motor-related process is involved. Patients with a diffuse, non-localized disease were almost unable to establish CR. This was also true for a patient with a focal surgical lesion with no CR on the affected side but who, simultaneously, showed an essentially normal CR incidence on the intact side. During US-alone trials healthy controls exhibited a remarkable decay of the UR amplitude due to a non-associative motor-related process such as habituation. The decay was most prominent in the paired trials section. In contrast, patients showed no significant differences in the UR amplitude throughout the entire recording session. Analysis of the CVP supported the electrophysiological findings, showing CR in the controls only. The differences between the responses of control subjects and those of the cerebellar patients imply strongly that the cerebellum is involved critically in controlling associative and non-associative motor-related processes.
    Experimental Brain Research 10/2004; 158(2):163-79. DOI:10.1007/s00221-004-1889-y · 2.17 Impact Factor