title: On the relationship between cortical excitability and visual oscillatory responses - A concurrent tDCS-MEG study.
abstract: Neuronal oscillations in the alpha band (8-12Hz) in visual cortex are considered to instantiate 'attentional gating' via the inhibition of activity in regions representing task-irrelevant parts of space. In contrast, visual gamma-band activity (40-100Hz) is regarded as representing a bottom-up drive from incoming visual information, with increased synchronisation producing a stronger feedforward impulse for relevant information. However, little is known about the direct relationship between excitability of the visual cortex and these oscillatory mechanisms. In this study we used transcranial direct current stimulation (tDCS) in an Oz-Cz montage in order to stimulate visual cortex, concurrently recording whole-brain oscillatory activity using magnetoencephalography (MEG) whilst participants performed a visual task known to produce strong modulations of alpha- and gamma-band activity. We found that visual stimuli produced expected modulations of alpha and gamma - presenting a moving annulus stimulus led to a strong gamma increase and alpha decrease - and that this pattern was observable both during active (anodal and cathodal) tDCS and sham tDCS. However, tDCS did not seem to produce systematic alterations of these oscillatory responses. The present study thus demonstrates that concurrent tDCS/MEG of the visual system is a feasible tool for investigating visual neuronal oscillations, and we discuss potential reasons for the apparent inability of tDCS to effectively change the amplitude of visual stimulus induced oscillatory responses in the current study.
authors.affiliation: Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, 6525 EN Nijmegen, The Netherlands. Electronic address: t.marshall@donders.ru.nl.
authors.forename: Tom R
authors.initials: TR
authors.lastname: Marshall
authors.affiliation: Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, 6525 EN Nijmegen, The Netherlands.
authors.forename: Sophie
authors.initials: S
authors.lastname: Esterer
authors.affiliation: Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, 6525 EN Nijmegen, The Netherlands.
authors.forename: Jim D
authors.initials: JD
authors.lastname: Herring
authors.affiliation: Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, 6525 EN Nijmegen, The Netherlands; Institute of Psychology, Christian-Albrechts University of Kiel, 24118 Kiel, Germany; Department of Neurology & Stroke, and Hertie Institute for Clinical Brain Research, University of Tübingen, 72076 Tübingen, Germany; Institute for Medical Psychology and Behavioral Neurobiology, University of Tübingen, 72076 Tübingen, Germany.
authors.forename: Til O
authors.initials: TO
authors.lastname: Bergmann
authors.affiliation: Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, 6525 EN Nijmegen, The Netherlands; Swammerdam Institute for Life Sciences - Center for Neuroscience, University of Amsterdam, Science Park 904, Amsterdam, XH 1098 The Netherlands.
authors.forename: Ole
authors.initials: O
authors.lastname: Jensen
mesh_terms: D001683:Biological Clocks / Q000502:physiology; D001931:Brain Mapping / Q000379:methods; D058256:Brain Waves / Q000502:physiology*; D000071080:Cortical Excitability / Q000502:physiology*; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D006801:Humans; D015225:Magnetoencephalography / Q000379:methods*; D008297:Male; D010775:Photic Stimulation; D065908:Transcranial Direct Current Stimulation / Q000379:methods*; D014793:Visual Cortex / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*; D055815:Young Adult