A POSITRON EMISSION TOMOGRAPHY STUDY OF ESSENTIAL TREMOR - EVIDENCE FOR OVERACTIVITY OF CEREBELLAR CONNECTIONS

The origin of essential tremor is unknown. Animal models have suggeste d that the inferior olivary nucleus may act as a tremor generator. We used positron emission tomography to study changes in regional cerebra l blood flow associated with involuntary postural tremor and passive w rist oscillation in patients with essential tremor. Activation due to voluntary wrist oscillation and arm extension without tremor was studi ed in normal control subjects. The essential tremor group had bilatera lly increased cerebellar blood flow at rest (without tremor) compared with the control group. Involuntary postural tremor was associated wit h further bilateral cerebellar activation, and also contralateral stri atal, thalamic, and sensorimotor cortex activation. Voluntary wrist os cillation, maintained arm extension without tremor, and passive wrist oscillation were all associated with significant ipsilateral rather th an bilateral cerebellar activation. We conclude that essential tremor is associated with increased bilateral cerebellar activity both at res t and during tremor.