Figure 12

Inability to adapt to damping in cerebellar hypometria during fast reverse movements. Movement (top panels) and the associated EMG bursts in a control subject (left panels) and in an ataxic patient (right panels) for an aimed target of 0.3 rad are illustrated. Top panels: superimposition of fast reversal movements performed without damping (blue), with addition of 0.1 Nms/rad (black) or 0.2 Nms/rad (red). EMG bursts in the flexor carpi radialis (FCR) and the extensor carpi radialis (ECR) are calibrated with a reference to a maximal isotonic contraction (MIC) from 0 to 6 Nm (a.u.: arbitrary units). In each position panel, grey areas correspond to the 99% confidence interval of control values of movement amplitudes in the basal mechanical state (no addition of damping); dotted lines in black and red delineate the 99% confidence interval of control values during addition of 0.1 Nms/rad and 0.2 Nms/rad, respectively. In the patient, the first phase of movement (from the starting position to the target of 0.3 rad) remains accurate but the second phase (from the target of 0.3 rad to the return to the initial position) is hypometric. The hypometria is increased with addition of damping. Arrowheads located near the EMG traces indicate the onset of EMG bursts (blue: no damping, black: addition of 0.1 Nms/rad, red: addition of 0.2 Nms/rad). AGO1, AGO2 and ANTA1 correspond to the first burst in the FCR, the second burst in the FCR and the antagonist burst in the ECR, respectively. Arrowheads near AGO1, ANTA1, AGON2 and ANTA2 correspond to the onset of the first burst in the FCR, the first phase of the burst in the ECR, the second phase of the burst in the ECR, and the second burst in the FCR, respectively. AGO1 and ANTA2 are well demarcated in bottom left panel, unlike in the right bottom panel. Flex.: direction of flexion of the wrist; Ext.: wrist extension.