Essential tremor (ET) probably represents the most common movement disorders in adults. Dysfunction of cerebellar system involving cerebello-rubral-thalamic loop was mostly suggested in the pathogenesis of ET. However, tremor eliminated after cerebral vascular insults over the corresponding motor cortex were reported in some patients. Electrophysiological studies demonstrated regional cortical activity in accordance with the tremor frequency and the tremor easily being reset by single magnetic shock over primary motor cortex, implying the cerebral cortex may participate in the tremor generation.To investing the mechanisms response for alternating the amplitude of electromyogram (EMG) response to transcranial magnetic stimulation (TMS) after prior conditioning of continuous theta-burst stimulation (cTBS), a well-known efficient intervention tool producing transient plastic change over regional cortex, to primary motor cortex (M1) or premotor cortex (PM) in patients with ET.We compared the physiological parameters including motor evoked potential (MEP), cortical silent period (CSP) and short-interval intracortical inhibition (SICI) before and after applying cTBS of 600 pulses at an intensity of 80% action motor threshold to M1 or PM in normal control (NC) and patients of ET.(1) Although cTBS given to either M1 or PM was capable of producing suppression effect on the motor cortical excitability in ET patients, the effects lasted much shorter as compared to those on NCs. (M1 cTBS, Fig. 1; PM cTBS, Fig. 2) (2) The amount of intra-cortical inhibition was decreased in NCs after applying cTBS on either M1 or PM. In contrast, no signify change was found after applying the same method to ET patients. (3) CSP was insignificantly prolonged by either M1 or PM cTBS in control group but not in ET patients.In this study, we failed to clarify the role of PM in the pathogenesis of ET. However, reduced plasticity and less modifiable motor cortical inhibitory circuits in response to M1 and PM TBS supported the theory of GABA defect in ET.
