Abnormal Movement-related Cortical Potentials in Patients with Holmes Tremor and Cerebellar Degeneration

Movement-related cortical potential (MRCP) represents function of the cerebello-thalamo-cortical circuit.

To elucidate the functional role of the olivodentatorubral pathway and the cerebellum on the motor cortex (M1), we analyzed MRCP in patients with Holmes' tremor, cerebellar degeneration, and healthy controls.

Three patients with Holmes' tremor in their right arms, four patients with cerebellar degeneration, and eight healthy subjects were studied. MRCP was recorded from 26 scalp Ag/AgCl cup electrodes when a self-paced, brisk voluntary extension of the wrist with a rate of every 7 s was performed. The MRCP components, including negative slope (NS') and frontal peak of the motor potential (fpMP), were analyzed. Nonparametric statistics (Mann-Whitney) were used to calculate the amplitude difference between the groups.

Compared with the healthy control group, the Holmes' tremor group revealed a significant reduction of the fpMP amplitude in the frontal midline electrode FCZ. The reduction of the mean amplitude of NS' was found in the posterior-scalp region for right-hand movement. The cerebellum degeneration group showed a significant prolongation of the fpMP latency and a significant decrease of the fpMP amplitude. In addition, a reduced mean amplitude of the NS' on the midline and the central region contralateral to the hand movement was noted.

Findings suggest that the cerebellum plays a pivotal role in compositing both the negative shifting before the movement onset and the motor potential (MP) after the movement onset. Its associated circuits mediating Holmes' tremor might influence only the amplitude of the MP after the movement onset.