Applications of neuromodulation to explore vestibular cortical processing; new insights into the effects of direct current cortical modulation upon pursuit, VOR and VOR suppression

Issue title: The Vestibular System: A Clinical and Scientific Update in Siena. In honor of Professor Daniele Nuti, Siena, Italy, April 5–6, 2013

Guest editors: Marco Mandalàx, Stefano Ramaty and David S. Zee

Article type: Research Article

Authors: Ahmad, H. | Arshad, Q. | Siddiqui, S. | Nigmatullina, Y. | Patel, M. | Bronstein, A.M. | Roberts, R.E.^{; *}

Affiliations: Department of Neuro-otology, Division of Brain Sciences, Charing Cross Hospital Campus, Imperial College London, London, UK | [x] Otological and Skull Base Surgery Department, S.M. delle Scotte Hospital, Siena, Italy | [y] Department of Electrical, Computer and Biomedical Engineering, University of Pavia, Pavia, Italy

Correspondence: [*] Corresponding author: R.E. Roberts, Department of Neuro-otology, Division of Brain Sciences, Charing Cross Hospital Campus, Imperial College London, Fulham Palace Road, London W6 8RF, UK. E-mail: [email protected]

Abstract: Functional imaging, lesion studies and behavioural observations suggest that vestibular processing is lateralised to the non-dominant hemisphere. Moreover, disruption of interhemispheric balance via inhibition of left parietal cortex using transcranial direct current stimulation (tDCS) has been associated with an asymmetric suppression of the vestibulo-ocular reflex (VOR). However, the mechanism by which the VOR was modulated remains unknown. In this paper we review the literature on non-invasive brain stimulation techniques which have been used to probe vestibular function over the last decade. In addition, we investigate the mechanisms whereby tDCS may modulate VOR, e.g. by acting upon pursuit, VOR suppression mechanisms or direct VOR modulation. We applied bi-hemispheric parietal tDCS in 11 healthy subjects and only observed significant effects on VOR gain (tdcs * condition p=0.041) – namely a trend for VOR gain increase with right anodal/left cathodal stimulation, and a decrease with right cathodal/left anodal stimulation. Hence, we suggest that the modulation of the VOR observed both here and in previous reports, is directly caused by top-down cortical control of the VOR as a result of disruption to interhemispheric balance, likely parietal.

Keywords: VOR, pursuit, interhemispheric, brain stimulation, vestibular

DOI: 10.3233/VES-140530

Journal: Journal of Vestibular Research, vol. 24, no. 5-6, pp. 453-458, 2014