title: Flicker-Driven Responses in Visual Cortex Change during Matched-Frequency Transcranial Alternating Current Stimulation.
abstract: We tested a novel combination of two neuro-stimulation techniques, transcranial alternating current stimulation (tACS) and frequency tagging, that promises powerful paradigms to study the causal role of rhythmic brain activity in perception and cognition. Participants viewed a stimulus flickering at 7 or 11 Hz that elicited periodic brain activity, termed steady-state responses (SSRs), at the same temporal frequency and its higher order harmonics. Further, they received simultaneous tACS at 7 or 11 Hz that either matched or differed from the flicker frequency. Sham tACS served as a control condition. Recent advances in reconstructing cortical sources of oscillatory activity allowed us to measure SSRs during concurrent tACS, which is known to impose strong artifacts in magnetoencephalographic (MEG) recordings. For the first time, we were thus able to demonstrate immediate effects of tACS on SSR-indexed early visual processing. Our data suggest that tACS effects are largely frequency-specific and reveal a characteristic pattern of differential influences on the harmonic constituents of SSRs.
authors.affiliation: Centre for Cognitive Neuroscience, University of SalzburgSalzburg, Austria; Center for Mind/Brain Science, University of TrentoMattarello, Italy.
authors.forename: Philipp
authors.initials: P
authors.lastname: Ruhnau
authors.affiliation: Centre for Cognitive Neuroimaging, Institute of Neuroscience and Psychology, University of Glasgow Glasgow, UK.
authors.forename: Christian
authors.initials: C
authors.lastname: Keitel
authors.affiliation: Centre for Cognitive Neuroscience, University of Salzburg Salzburg, Austria.
authors.forename: Chrysa
authors.initials: C
authors.lastname: Lithari
authors.affiliation: Centre for Cognitive Neuroscience, University of Salzburg Salzburg, Austria.
authors.forename: Nathan
authors.initials: N
authors.lastname: Weisz
authors.affiliation: Centre for Cognitive Neuroscience, University of Salzburg Salzburg, Austria.
authors.forename: Toralf
authors.initials: T
authors.lastname: Neuling
keywords: MEG; NIBS; alpha rhythm; brain oscillation; entrainment; frequency tagging; steady-state response; tACS