The link between cortical excitability and visual oscillatory response: A concurrent tDCS and MEG study

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Neuronal oscillations limit and prioritize neuronal communication during visual information processing. Modulations of alpha-band oscillations (8-12 Hz) are thought to reflect top-down inhibitory modulation of activity in sensory regions representing task-irrelevant visual space, whereas bottom-up processing of visual stimuli is achieved by synchronisation in the gamma band (30-100 Hz). However, the causal interactions between cortical excitability and oscillatory modulations in the alpha- and gamma-band have scarcely been investigated in human participants. We used transcranial direct current stimulation (tDCS) to directly manipulate excitability during the simultaneous recording of MEG data. Participants performed a simple visual task known to reliably induce modulations of alpha- and gamma-band oscillations. We show that alpha- and gamma-band activity in response to the visual stimuli can consistently be retrieved despite substantial signal artefacts in the raw MEG data. Thus, this study provides first evidence that tDCS can be applied over the visual cortex during simultaneous recording of MEG data. However, based on our analysis, occipital tDCS does not appear to systematically modulate alpha and gamma oscillations. We discuss possible reasons for the observed absence of tDCS effects on visual oscillatory activity.
Faculteit der Sociale Wetenschappen