title: The role of the posterior cerebellum in saccadic adaptation: a transcranial direct current stimulation study.
abstract: The posterior vermis of the cerebellum is considered to be critically involved in saccadic adaptation. However, recent evidence suggests that the adaptive decrease (backward adaptation) and the adaptive increase (forward adaptation) of saccade amplitude rely on partially separate neural substrates. We investigated whether the posterior cerebellum could be differentially involved in backward and forward adaptation by using transcranial direct current stimulation (TDCS). To do so, participants' saccades were adapted backward or forward while they received anodal, cathodal, or sham TDCS. In two extra groups, subjects underwent a nonadaptation session while receiving anodal or cathodal TDCS to control for the direct effects of TDCS on saccadic execution. Surprisingly, cathodal stimulation tended to increase the extent of both forward and backward adaptations, while anodal TDCS strongly impaired forward adaptation and, to a smaller extent, backward adaptation. Forward adaptation was accompanied by a greater increase in velocity with cathodal stimulation, and reduced duration of change for anodal stimulation. In contrast, the expected velocity decrease in backward adaptation was noticeably weaker with anodal stimulation. Stimulation applied during nonadaptation sessions did not affect saccadic gain, velocity, or duration, demonstrating that the reported effects are not due to direct effects of the stimulation on the generation of eye movements. Our results demonstrate that cerebellar excitability is critical for saccadic adaptation. Based on our results and the growing evidence from studies of vestibulo-ocular reflex and saccadic adaptation, we conclude that the plasticity at the level of the oculomotor vermis is more fundamentally important for forward adaptation than for backward adaptation.
authors: Nuffield Department of Clinical Neurosciences, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DU, United Kingdom, muriel.panouilleres@ndcn.ox.ac.uk.
authors: Muriel T N
authors: http://orcid.org/0000-0003-0264-2093
authors: MT
authors: Panouillères
authors: Behavioural Brain Sciences Centre, School of Psychology, University of Birmingham, Birmingham B15 2TT, United Kingdom, and.
authors: R Chris
authors: http://orcid.org/0000-0003-3002-1251
authors: RC
authors: Miall
authors: Nuffield Department of Clinical Neurosciences, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DU, United Kingdom, School of Sport, Exercise and Rehabilitation Sciences, The University of Birmingham, Birmingham B15 2TT, United Kingdom.
authors: Ned
authors: http://orcid.org/0000-0002-6803-486X
authors: N
authors: Jenkinson
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000328:Adult; D000704:Analysis of Variance; D001703:Biophysics; D002531:Cerebellum / Q000502:physiology*; D005260:Female; D006801:Humans; D007259:Infrared Rays; D008297:Male; D011930:Reaction Time; D012438:Saccades / Q000502:physiology*; D013997:Time Factors; D065908:Transcranial Direct Current Stimulation; D055815:Young Adult
keywords: TDCS; adaptation; cerebellum; saccades