Objective: Investigate whether frequency- and phase-specific transcranial alternating current stimulation (TACS) over the primary motor cortex and cerebellum influences tremor in dystonia and essential tremor.

Background: Tremor is caused by pathological oscillatory activity in the cerebello-thalamo-cortical circuit. Possibly, this pathological rhythm can be suppressed by TACS. To achieve this, stimulation should be fine-tuned to the ongoing tremor frequency and phase as was previously shown to be effective in Parkinson’s disease [1]. Here we explore this intervention in essential tremor and dystonia.

Methods: In this ongoing study, currently 7 patients were studied (5 with tremor and dystonia, and 2 with essential tremor). Patients were instructed to assume an individually defined hand posture that evoked tremor, during 30s trials. On each trial, TACS over the central sulcus (contralateral to tremor) or the cerebellum (ipsilateral to tremor) was applied at the individual tremor frequency at 10 different phase angles with regard to the ongoing tremor (36 degree increments, 10 trials for each of the two stimulation sites). This was achieved by a closed-loop system that used the ongoing tremor, as measured with accelerometry, to deliver frequency- and phase-specific stimulation with a 2 mA peak-to-peak amplitude. Power at the tremor frequency (measured with an accelerometer) provided a measure of tremor severity during each trial.

Results: During central sulcus stimulation, tremor power was dependent on the phase difference between the ongoing tremor and the TACS signal [figure1]. We observed reduced tremor power during stimulation with a 72-degree and a 252-degree phase difference. This pattern was clear at the group level, but also detectable in each individual. Cerebellar stimulation did not affect tremor amplitude.

Conclusions: These preliminary data suggests that phase-specific TACS over the primary motor cortex can reduce tremor severity in essential tremor and dystonia. More patients will be included in the upcoming months, which will enable well-powered statistical testing and a comparison between dystonic and essential tremor patients. Final data will be presented at the meeting.

References: 1. Brittain, J.S., et al., Tremor Suppression by Rhythmic Transcranial Current Stimulation. Current Biology, 2013. 23(5): p. 436-440.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/tremor-suppression-by-phase-specific-transcranial-alternating-current-stimulation-in-dystonia-and-essential-tremor/