Role of cerebellum in the control of hand and foot associated movements

Motor co-ordination was investigated in seven subjects who underwent surgical treatment because of vascular or neoplastic lesions confined to the cerebellar vermis (3) or to one of the hemispheres (4) and in six subjects affected by olivo-ponto-cerebellar atrophy (OPCA). Subjects, tested ipsilaterally to the lesion, were asked to couple in a parasagittal plane in-phase rhythmical oscillations of the prone hand and the ipsilateral foot. Movement frequency, paced by a metronome, varied in different series (10sec each) from 0.6 to 3 Hz. Hand and foot angular displacements were measured by a potentiometric technique; EMGs from Extensor Carpi Radialis (ECR) and Tibialis Anterior (TA) were recorded by surface electrodes. The phase-relations between hand and foot movements, as well as between ECR and TA EMG onsets, were calculated. For each segment, the phase-relation between EMG onset and the onset of the related movement was also determined over the whole frequency range (frequency-response curve). The experiment was repeated with the same schedule after applying a mass of 3 kg concentric to the rotation axis of the wrist (inertial momentum 15 gm2). All subjects with primary cerebellar lesion performed in-phase oscillations up to frequencies of 2.2-2.8 Hz, i.e. slightly lower then healthy subjects. In each of them hand and foot had similar mechanical properties, as revealed by the similar frequency-response curves, but “hemispheric” and “vermian” patients showed distinct behaviours in the inter-limb phase relations. In “hemispheric” patients, the phase-lag of the hand movement, with respect to foot movement, increased with frequency. The same did, given the similar mechanical properties of the two segments, the phase-lag between the onset of ECR EMG and onset of TA EMG. Thus, to account for this progressive increase of phase-lag, these subjects generated a constant time-delay between hand and foot activation, the contrary of what happen in normal subjects. In contrast, in “vermian” patients the hand movement lagged that of the foot of about 40° over the whole frequency range and parallely the ECR onset lagged the TA onset of about 10°. These subjects were then able to generate a variable time-delay between ECR an TA activation, which decrease with frequency. This suggests that “vermian” patients could still monitor the movement and use this information to compensate for frequency. In all these patients hand loading resulted in a sensible reduction of the movement maximal frequency (1.8-2 Hz) but, unexpectedly, the phase-shift between movements was only slightly worsened. This indicates that all patients detected the new biomechanical conditions and could compensate for it. However, this compensation was larger in patients with “vermian” lesions Also in OPCA patients, who performed the task only up to 1.6 Hz, hand and foot had similar mechanical properties, as witnessed by the frequency-response curves. It was thus required that they synchronised muscle activation to produce synchronous movements. However, this strategy was adopted only at low movement frequency. At high frequency, instead, they displayed a small but progressive phase-delay in TA activation that resulted in a progressive lag of foot oscillation. In all patients, a small lag (10-20°) of the hand cycle was present at the lowest frequencies, which gradually faded, and reverted in a hand advance (40-50°) above 1.2Hz. A similar behaviour was observed between ECR and TA onsets. Hand loading resulted in all subjects, but one, in a strong reduction of the maximal frequency of oscillation (0.8Hz) and in a dramatic increase of the hand phase-lag, as if they could not compensate for the new mechanical properties of the hand. Thus these patients seems to apply, as normal subjects do, a scheme of compensation to frequency increase, without perceiving the mechanical properties of two segments.