Disturbances of antagonistic neck innervation in patients with cerebellar deficits

Fast 60 degree head rotations of nine patients with cerebellar deficits were analysed and compared with those of nine normal subjects. The surface EMG activity from both Splenii capitis muscles were recorded. The triphasic pattern of reciprocal innervated neck muscles with regard to the duration, amplitude and onset of the pulses were analysed together with the dynamic features of head rotation, i.e. position and acceleration profiles. The deviation of the onset of the antagonistic (B) pulse of the EMG-pattern flow was substantially increased. In most cases the onset of the B-pulse was delayed, less premature and sporadic regular onsets occurred. The number of co-contractions and multiple antagonistic pulses was significantly increased. Half of the movements of patients were found to be dysmetric, with an irregular flow of position and acceleration functions. From these, mainly hypermetric movements occurred. The number of irregular pulse patterns was higher than the number of dysmetrias. In this context cocontractions, multiple antagonistic pulses and cortical control can be discussed as strategies of the cerebellar patients to improve their dynamic output. Our experiments support the notion of the cerebellum playing an important part in the temporal integration of an antagonistically innervated movement. The measurement of electromyographic burst patterns can be used as a clinical tool to demonstrate an insufficient timing of the activities of muscles involved.