Question:

In his famous work on patients presenting acute cerebellar injuries (Brain, Vol. 40, pp. 461 - 535, 1917) Gordon Holmes demonstrated that some exemplary patients with unilateral damage (N=3) showed a delayed start of auxometric finger movements as well as incomplete force production. The aim of this study was to investigate these results in more detail.

Methodology:

Patients presenting with cerebellar lesions (N=11, age: 52.1 years) and control subjects (N=11, age: 50.7 years) performed a sequence of precise auxometric finger movements with a custom-made dynamometer. It consists of a hinge (58 mm legs) which was kept open by a leg spring at an angle of 11 deg. The spring had a constant of 39.4 Nmm/deg resulting in a force range of 8.7 N (initial value) to 16.2 N (maximal value). Subjects had to squeeze the hinge each time a 1 kHz tone (duration: 2 s) was presented. During each trial the tone was presented twice with a constant inter-stimulus interval of 2 s. Between each trial a random interval of 10 - 15 s was allowed. Median values for reaction time (RT) and movement time (MT) of both hands were compared statistically. During the procedure electro-myographic activity (EMG) of the thenar muscle (TH) and first dorsal interosseus muscle (FDI) were recorded.

Results:

Regardless of the hand in use, RT and MT of the two movements in the sequence were significantly increased (both p<0.01) in the patient group (CBL) compared with the control group (CTRL). Interestingly, for the right hand RT and MT of the second movement were reduced (both p<0.01) compared with the first movement (RT: 420 vs. 338 ms, MT: 250 vs. 202 ms, respectively) in CBL, indicating an improvement of movement performance when timing is constant. The EMG-onsets of both muscles were significantly later in CBL than in CTRL. Detailed analysis revealed that the median EMG-onset asynchronicity between TH and FDI is significantly greater in CBL (right hand 41 ms, left hand 36 ms) than in CTRL (right hand 13 ms, left hand 17 ms), suggesting better co-ordination of the muscles around the thumb joint in CTRL.

Conclusions:

Patients presenting with cerebellar lesions have more difficulties in starting precise auxometric finger movements. This is, in part, due to the fact that the co-ordination of co-acting muscles around a joint is limited. Nevertheless, they can improve in performing simple movements when timing remains constant.

Supported by the “Else-Kröner-Fresenius Stiftung” (A12/07).