Effects of changes in mechanical state of limb on cerebellar intention tremor

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Abstract
Cooling through cryoprobe sheaths implanted alongside the dentate nucleus of the cerebellum in 3 Cebus monkeys resulted in a 3-5 Hz tremor in the ipsilateral forelimb, which was evident during rapid movements and following arm perturbations. The character of the tremor was altered by mechanical loads applied to the limb: the frequency was increased by addition of spring stiffness and by an increase in constant torque, and decreased by addition of mass. The amplitude of the tremor was decreased by an increase in viscous resistance. Randomly timed perturbations applied to the forearm resynchronized the phase of the tremor. During cerebellar nuclear cooling the EMG [electromyogram] responses to limb perturbations sometimes showed an increase in the segmental response, while later responses exhibited little change. Cerebellar tremor may originate from instability in 1 or more reflex pathways. The lack of increase of the late EMG responses during cerebellar cooling, suggested that the tremor is not due simply to an increase in gain in suprasegmental reflex pathways.

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