Coupling of hand and foot voluntary oscillations in patients suffering cerebellar ataxia: different effect of lateral or medial lesions on coordination

Pediatric Slow-Progressive, but Not Non-Progressive Cerebellar Ataxia Delays Intra-Limb Anticipatory Postural Adjustments in the Upper Arm

We recently investigated the role of the cerebellum during development, reporting that children with genetic slow-progressive ataxia (SlowP) show worse postural control during quiet stance and gait initiation compared to healthy children (H). Instead, children with genetic non-progressive ataxia (NonP) recalled the behavior of H. This may derive from compensatory networks, which are hindered by disease progression in SlowP while free to develop in NonP. In the aim of extending our findings to intra-limb postural control, we recorded, in 10 NonP, 10 SlowP and 10 H young patients, Anticipatory Postural Adjustments (APAs) in the proximal muscles of the upper-limb and preceding brisk index finger flexions. No significant differences in APA timing occurred between NonP and H, while APAs in SlowP were delayed. Indeed, the excitatory APA in Triceps Brachii was always present but significantly delayed with respect to both H and NonP. Moreover, the inhibitory APAs in the Biceps Brachii and Anterior Deltoid, which are normally followed by a late excitation, could not be detected in most SlowP children, as if inhibition was delayed to the extent where there was overlap with a late excitation. In conclusion, disease progression seems to be detrimental for intra-limb posture, supporting the idea that inter- and intra-limb postures seemingly share the same control mechanism.

Postural Control in Children with Cerebellar Ataxia

Controlling posture, i.e., governing the ensemble of involuntary muscular activities that manage body equilibrium, represents a demanding function in which the cerebellum plays a key role. Postural activities are particularly important during gait initiation when passing from quiet standing to locomotion. Indeed, several studies used such motor task for evaluating pathological conditions, including cerebellar disorders. The linkage between cerebellum maturation and the development of postural control has received less attention. Therefore, we evaluated postural control during quiet standing and gait initiation in children affected by a slow progressive generalized cerebellar atrophy (SlowP) or non-progressive vermian hypoplasia (Joubert syndrome, NonP), compared to that of healthy children (H). Despite the similar clinical evaluation of motor impairments in NonP and SlowP, only SlowP showed a less stable quiet standing and a shorter and slower first step than H. Moreover, a descriptive analysis of lower limb and back muscle activities suggested a more severe timing disruption in SlowP. Such differences might stem from the extent of cerebellar damage. However, literature reports that during childhood, neural plasticity of intact brain areas could compensate for cerebellar agenesis. We thus proposed that the difference might stem from disease progression, which contrasts the consolidation of compensatory strategies.

Temporal disruption of upper-limb anticipatory postural adjustments in cerebellar ataxic patients

Voluntary movements induce postural perturbations, which are counteracted by anticipatory postural adjustments (APAs) that preserve body equilibrium. Little is known about the neural structures generating APAs, but several studies suggested a role of sensory-motor areas, basal ganglia, supplementary motor area and thalamus. However, the role of the cerebellum still remains an open question. The aim of this present paper is to shed further light on the role of cerebellum in APAs organization. Thus, APAs that stabilize the arm when the index finger is briskly flexed were recorded in 13 ataxic subjects (seven sporadic cases, four dominant ataxia type III and two autosomal recessive), presenting a slowly progressive cerebellar syndrome with four-limb dysmetria, and compared with those obtained in 13 healthy subjects. The pattern of postural activity was similar in the two groups [excitation in triceps and inhibition in biceps and anterior deltoid (AD)], but apparent modifications in timing were observed in all ataxic subjects in which, on average, triceps brachii excitation lagged the onset of the prime mover flexor digitorum superficialis by about 27 ms and biceps and AD inhibition were almost synchronous to it. Instead, in normal subjects, triceps onset was synchronous to the prime mover and biceps and AD anticipated it by about 40 ms. The observed disruption of the intra-limb APA organization confirms that the cerebellum is involved in APA control and, considering cerebellar subjects as a model of dysmetria, also supports the view that a proper APA chain may play a crucial role in refining movement metria.

Effects of olivo-ponto-cerebellar atrophy (OPCA) on finger interaction and coordination

OBJECTIVES

We investigated changes in finger interaction and coordination in patients with olivo-ponto-cerebellar atrophy (OPCA) using the recently developed approach to motor synergies based on the principle of motor abundance.

METHODS

OPCA patients and control subjects performed sets of maximal and submaximal force production tasks by the fingers of each of the hands. Indices of multi-finger synergies were quantified within the framework of the uncontrolled manifold hypothesis.

RESULTS

The patients showed lower maximal forces, higher indices of finger interdependence (enslaving), and lower indices of multi-finger synergies stabilizing total force in four-finger tasks. In addition, the patients showed an impaired ability to adjust synergies in preparation to a quick action (small and delayed anticipatory synergy adjustments). The synergy indices showed significant correlations with the clinical scores (both UPDRS total motor scores and ataxia related sub-scores). The observed changes in the indices of finger interaction and coordination were qualitatively similar to those reported earlier for patients with Parkinson's disease; however, the magnitude of the changes was much higher in the OPCA group.

CONCLUSIONS

These findings fit the hypotheses on the role of the cerebellum in assembling motor synergies and in the feed-forward control of action. They suggest that the synergy index measured in artificial, constrained laboratory tasks may be predictive of more general changes in motor behavior.

SIGNIFICANCE

The results suggest that studies of multi-digit synergies may be particularly sensitive to subcortical disorders and may provide a much-needed tool for quantitative assessment of impaired coordination in such patients.

Cerebellar ataxia: pathophysiology and rehabilitation

This series of articles for rehabilitation in practice aims to cover a knowledge element of the rehabilitation medicine curriculum. Nevertheless they are intended to be of interest to a multidisciplinary audience. The competency addressed in this article is 'The trainee consistently demonstrates a knowledge of management approaches for specific impairments including spasticity, ataxia.'