title: Transcranial Direct Current Stimulation Effects on Single and Paired Flash Visual Evoked Potentials.
abstract: Transcranial direct current stimulation (tDCS) applied over the occipital cortex has a controversial effect on the visual cortex excitability. Paired flash visual evoked potentials (paired F-VEPs) offer a unique method to express neural inhibition within the visual system. However, no studies have explored the effects of tDCS on F-VEPs in humans. The aim of this study was to evaluate the changes of single- and paired-F-VEPs during and after tDCS in healthy humans. Twenty-six healthy volunteers participated. F-VEPs were recorded from occipital electrodes with closed eyes. Stimuli were single flashes, intermingled to flash pairs at the interstimulus interval of 125, 62.5, 50, 33.3, 16.6, and 11.1 ms (internal frequency of 8, 16, 20, 30, 60, and 90 Hz). The single F-VEP was split into a "main complex" and a "late response." As to paired stimuli, the "test" F-VEP emerged from electronic subtraction of the single-F-VEP to the paired-F-VEP. In experiment 1, the return electrode was located on the scalp and we studied changes in F-VEPs after anodal, cathodal (1 mA, 15 min) and sham stimulation. A second experiment was performed in which F-VEPs were recorded before, during and after tDCS stimulation (anodal and cathodal) with the return electrode on the neck. F-VEPs recorded in experiment 1 did not detect any significant change after tDCS. In experiment 2 anodal polarization significantly increased the P2 latency (P = .031) and reduced the amplitude of the "late response" of the single F-VEP (P = .008). As for the paired F-VEPs, no significant changes were detected. In conclusion, low-intensity anodal tDCS has weak inhibitory aftereffects on the single F-VEP and no effects on the paired F-VEPs. Further methodological studies are needed to improve polarization efficacy.
authors.affiliation: Sobell Department of Motor Neuroscience and Movement Disorders, University College London Institute of Neurology, London, UK Department of Translational Medicine, Section of Neurology, University of Piemonte Orientale "A. Avogadro", Novara, Italy gionata.strigaro@gmail.com.
authors.forename: Gionata
authors.initials: G
authors.lastname: Strigaro
authors.affiliation: Sobell Department of Motor Neuroscience and Movement Disorders, University College London Institute of Neurology, London, UK Department of Neurology, University Clinic Ulm, Ulm, Germany.
authors.forename: Isabella
authors.initials: I
authors.lastname: Mayer
authors.affiliation: Sobell Department of Motor Neuroscience and Movement Disorders, University College London Institute of Neurology, London, UK Neuroscience Laboratory, Department of Neurology, China Medical University Hospital, Taichung, Taiwan School of Medicine, China Medical University, Taichung, Taiwan.
authors.forename: Jui-Cheng
authors.initials: JC
authors.lastname: Chen
authors.affiliation: Department of Translational Medicine, Section of Neurology, University of Piemonte Orientale "A. Avogadro", Novara, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Cantello
authors.affiliation: Sobell Department of Motor Neuroscience and Movement Disorders, University College London Institute of Neurology, London, UK.
authors.forename: John C
authors.initials: JC
authors.lastname: Rothwell
mesh_terms: D000328:Adult; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D006801:Humans; D007266:Inhibition, Psychological; D008297:Male; D009433:Neural Inhibition / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods*; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D014793:Visual Cortex / Q000502:physiology*
keywords: evoked potentials; flash visual evoked potentials; paired stimulation; transcranial direct current stimulation; visual cortex