Objective: 

A characteristic symptom of cerebellar disease is decomposition of pointing movements. A similar symptom was found in an isometric precision grip task, in which the process of picking a raspberry is simulated. The aim of this study was to quantify such decomposition.

Methods: 

Pull force had to be increased in a smooth and linear fashion for a duration of 3 - 5.5 s. Decomposition was measured as systematic deviation of pull force from a single linear time trend in cerebellar patients (CBL, N=11) and healthy subjects (CTRL, N=11). The time of decomposition initiation (breakpoint) was estimated by a two-spline model.

Results: 

Decomposition of the task was found in both groups. The mean pull-force slope in CTRL was 2.4 times steeper before the breakpoint than afterwards (4.5 N/s and 1.8 N/s, respectively). In contrast, in CBL this pull-force slope was 9.6 times steeper before the breakpoint than after (7.3 N/s and 0.8 N/s, respectively). In addition, the time from the start of pulling to the breakpoint was significant shorter in CBL (mean = 1257 ms) than in CTRL (mean = 1551 ms).

Conclusion: 

The decomposition in the "picking the raspberry" task is a general behaviour in all subjects. Cerebellar patients, however, differ from control subjects since their pull act is restricted mainly to the first part of the movement with a hypermetric pull force slope compared with that of CTRL. Supported by the "Else-Kröner-Fresenius Stiftung" (A12/07)