TMS excitability study in essential tremor: Absence of gabaergic changes assessed by silent period recordings

Summary Background Essential tremor (ET) is thought to emerge from activity in a distributed cerebello-thalamo-cortical network. It has been proposed that the network goes into oscillation because of abnormal GABAergic inhibitory transmission. Objective To test this idea by investigating GABAergic circuitry in motor cortex using transcranial magnetic stimulation (TMS). Methods Motor cortex excitability was examined using TMS in 21 patients with essential tremor and in 20 control subjects. Resting and active motor threshold (RMT, AMT) and input–output curves examined corticospinal excitability. Contralateral silent period (cSP) at a different range of stimulation intensities, and the ipsilateral silent period (iSP) using a stimulus intensity of 150% RMT were used as measures of GABAergic function. Results RMT and AMT were significantly lower in patients than controls and patients had a steeper I/O curve. However, there were no significant differences in either cSP at different intensities or in iSP. Conclusion We found no evidence in favour of the GABA hypothesis in ET.