Objective: 

A characteristic symptom of cerebellar disease is decomposition of pointing movements. The aim of this study was to analyse characteristic changes in EMG activity leading to such decomposition.

Methods: 

Grip force and pull force were analysed in an isometric prehension task. Pull force had to be increased in a smooth and linear fashion. The time of decomposition initiation (breakpoint) was estimated by a two-spline model. The EMG activity of three muscles (thenar, first digital interossius (FDI), extensor digitorum communis (EDC)) preceding the breakpoint was studied in 11 healthy subjects (CTRL) and in 11 cerebellar patients (CBL) and the first peak of EMG activity was calculated.

Results: 

During the task, CTRL increased the activity of all three muscles continuously whereas CBL showed often rapidly increasing EMG activities before the breakpoint. After the start of pulling thenar and FDI activity first peaked after approximately 205 ms and the EDC after 243 ms. This might imply that thenar or FDI activity may influence the EDC activity. A trial-by-trial analysis, however, showed that the three muscles were not activated in a systematic sequence in CBL.

Conclusion: 

The initiation of decomposition was caused by a rapidly increasing EDC activity followed by a stabilisation of the activity before the breakpoint. EDC activity was not influenced by the activity of thenar or FDI muscles. Supported by the "Else-Kröner-Fresenius Stiftung" (A12/07)