Cerebellar ataxia: abnormal control of interaction torques across multiple joints

Abstract

1. We studied seven subjects with cerebellar lesions and seven control subjects as they made reaching movements in the sagittal plane to a target directly in front of them. Reaches were made under three different conditions: 1) "slow-accurate," 2) "fast-accurate," and 3) "fast as possible." All subjects were videotaped moving in a sagittal plane with markers on the index finger, wrist, elbow, and shoulder. Marker positions were digitized and then used to calculate joint angles. For each of the shoulder, elbow and wrist joints, inverse dynamics equations based on a three-segment limb model were used to estimate the net torque (sum of components) and each of the component torques. The component torques consisted of the torque due to gravity, the dynamic interaction torques induced passively by the movement of the adjacent joint, and the torque produced by the muscles and passive tissue elements (sometimes called "residual" torque). 2. A kinematic analysis of the movement trajectory and the change in joint angles showed that the reaches of subjects with cerebellar lesions were abnormal compared with reaches of control subjects. In both the slow-accurate and fast-accurate conditions the cerebellar subjects made abnormally curved wrist paths; the curvature was greater in the slow-accurate condition. During the slow-accurate condition, cerebellar subjects showed target undershoot and tended to move one joint at a time (decomposition). During the fast-accurate reaches, the cerebellar subjects showed target overshoot. Additionally, in the fast-accurate condition, cerebellar subjects moved the joints at abnormal rates relative to one another, but the movements were less decomposed. Only three subjects were tested in the fast as possible condition; this condition was analyzed only to determine maximal reaching speeds of subjects with cerebellar lesions. Cerebellar subjects moved more slowly than controls in all three conditions. 3. A kinetic analysis of torques generated at each joint during the slow-accurate reaches and the fast-accurate reaches revealed that subjects with cerebellar lesions produced very different torque profiles compared with control subjects. In the slow-accurate condition, the cerebellar subjects produced abnormal elbow muscle torques that prevented the normal elbow extension early in the reach. In the fast-accurate condition, the cerebellar subjects produced inappropriate levels of shoulder muscle torque and also produced elbow muscle torques that did not very appropriately with the dynamic interaction torques that occurred at the elbow. Lack of appropriate muscle torque resulted in excessive contributions of the dynamic interaction torque during the fast-accurate reaches. 4. The inability to produce muscle torques that predict, accommodate, and compensate for the dynamic interaction torques appears to be an important cause of the classic kinematic deficits shown by cerebellar subjects during attempted reaching. These kinematic deficits include incoordination of the shoulder and the elbow joints, a c...

Coordinated Turn-and-Reach Movements. I. Anticipatory Compensation for Self-Generated Coriolis and Interaction Torques

“…It means that the movements were not segmented so as to minimize self-generated Coriolis torques incumbent on torso rotation. This finding may be contrasted with those from investigations of pathological populations: in particular, decomposition of elbow and shoulder joint motions [a strategy that reduces the interaction torques at the moving joint (Bastian et al 1996)] and transient locking of the elbow joint (Sainburg et al 1993) have been observed in slow reaching movements performed by cerebellar subjects and in "slicing" gestures performed by deafferented subjects, respectively.…”

Cerebellar learning of accurate predictive control for fast-reaching movements

“…Moreover, both populations exhibited shifts in activity during movements. Bastian et al (1996a) found that cerebellar subjects performing fast-reaching movements often generate inappropriate muscle torques relative to the dynamic interaction torques. The inability to produce muscle torques that compensate for the dynamic interaction torques appears to be an important cause of the de®cits shown by cerebellar subjects during reaching.…”

Force related activations in rhythmic sequence production

“…Functional imaging studies have identified the cerebellum in the regulation of velocity and extent of movement (Turner et al, 2003a). However, in these studies, interaction torques may have played a significant role, especially given that altered control of interaction torques underlies impaired multijoint reaching movements observed in cerebellar disease (Bastian et al, 1996). However, in the near isometric conditions of the present study, no such torques arise, which identifies the cerebellar activation with pure force control, although this may have included monitoring of force either through efferent or afferent signals.…”