title: Applications of neuromodulation to explore vestibular cortical processing; new insights into the effects of direct current cortical modulation upon pursuit, VOR and VOR suppression.
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.
authors.affiliation: Department of Neuro-otology, Division of Brain Sciences, Charing Cross Hospital Campus, Imperial College London, London, UK.
authors.forename: H
authors.initials: H
authors.lastname: Ahmad
authors.affiliation: Department of Neuro-otology, Division of Brain Sciences, Charing Cross Hospital Campus, Imperial College London, London, UK.
authors.forename: Q
authors.initials: Q
authors.lastname: Arshad
authors.affiliation: Department of Neuro-otology, Division of Brain Sciences, Charing Cross Hospital Campus, Imperial College London, London, UK.
authors.forename: S
authors.initials: S
authors.lastname: Siddiqui
authors.affiliation: Department of Neuro-otology, Division of Brain Sciences, Charing Cross Hospital Campus, Imperial College London, London, UK.
authors.forename: Y
authors.initials: Y
authors.lastname: Nigmatullina
authors.affiliation: Department of Neuro-otology, Division of Brain Sciences, Charing Cross Hospital Campus, Imperial College London, London, UK.
authors.forename: M
authors.initials: M
authors.lastname: Patel
authors.affiliation: Department of Neuro-otology, Division of Brain Sciences, Charing Cross Hospital Campus, Imperial College London, London, UK.
authors.forename: A M
authors.initials: AM
authors.lastname: Bronstein
authors.affiliation: Department of Neuro-otology, Division of Brain Sciences, Charing Cross Hospital Campus, Imperial College London, London, UK.
authors.forename: R E
authors.initials: RE
authors.lastname: Roberts
mesh_terms: D000328:Adult; D001307:Auditory Perception / Q000502:physiology*; D004558:Electric Stimulation / Q000379:methods; D005133:Eye Movements / Q000502:physiology; D005260:Female; D019416:Head Movements / Q000502:physiology; D006801:Humans; D008297:Male; D012027:Reflex, Vestibulo-Ocular / Q000502:physiology*; D012196:Review Literature as Topic; D065855:Spatial Processing / Q000502:physiology; D050781:Transcranial Magnetic Stimulation / Q000379:methods; D014724:Vestibular Function Tests; D014722:Vestibule, Labyrinth / Q000502:physiology; D055815:Young Adult
keywords: VOR; brain stimulation; interhemispheric; pursuit; vestibular