Montage matters: the influence of transcranial alternating current stimulation on human physiological tremor.
Bottom Line: We implemented a sham-controlled experimental protocol where the position of the stimulating electrode remained fixed, overlying primary motor cortex, whilst the position of the return electrode varied between two cephalic (fronto-orbital and contralateral primary motor cortex) and two extracephalic (ipsilateral and contralateral shoulder) locations.Altering only the position of the return electrode had a profound behavioral effect: only the montage with extracephalic return contralateral to the primary stimulating electrode significantly entrained physiological tremor (15.9% ± 6.1% increase in phase stability, 1 S.E.M.).Photic stimulation also entrained tremor (11.7% ± 5.1% increase in phase stability).
Affiliation: Experimental Neurology Group, Division of Clinical Neurology, Nuffield Department of Clinical Neurosciences, Medical Sciences Division, University of Oxford, Level 6, West Wing, John Radcliffe Hospital, Oxford OX3 9DU, United Kingdom.Show MeSH
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Mentions: To address the principal question of whether the position of the return electrode significantly influences the effect of stimulation, we kept the primary stimulation site constant (left primary motor cortex, M1), whilst the return electrode was rotated between four possibilities: two cephalic positions – fronto-orbital (FO) and contralateral (right) primary motor cortex (cM1) – and two extracephalic positions – right and left shoulder (RSh and LSh, respectively; Fig. 1). These locations reflect the most common arrangements used by the tES motor community, and have been chosen to offer a broad range of expected current flow patterns. In particular, the cephalic positions have traditionally dominated motor tES studies, offering distinct current density distributions (e.g., Ref. ), whilst extracephalic positions have already proven effective in similar tremor paradigms , , .
Affiliation: Experimental Neurology Group, Division of Clinical Neurology, Nuffield Department of Clinical Neurosciences, Medical Sciences Division, University of Oxford, Level 6, West Wing, John Radcliffe Hospital, Oxford OX3 9DU, United Kingdom.