Flicker-Driven Responses in Visual Cortex Change during Matched-Frequency Transcranial Alternating Current Stimulation.

Philipp Ruhnau,Christian Keitel,Nathan Weisz,Chrysa Lithari,Toralf Neuling

doi:10.3389/fnhum.2016.00184

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.

Highlights

Neural rhythms are prime candidates for a universal means of communication within and across brain regions and may code information from bits up to full objects (Engel et al, 2001; Buzsáki and Draguhn, 2004)
Compared to classic electrophysiological research, transcranial alternating current stimulation (tACS) is in principle a more direct means to probe the role of brain oscillations in cognition: a strictly periodically alternating current is applied to modify brain rhythms directly that have been previously implicated with cognitive function
The present study shows that: (1) recording steady-state responses (SSRs) in MEG during concurrent tACS, and a combination of both methods of brain stimulation, is feasible

Summary

Introduction

Neural rhythms are prime candidates for a universal means of communication within and across brain regions and may code information from bits up to full objects (Engel et al, 2001; Buzsáki and Draguhn, 2004). Compared to classic electrophysiological research, tACS is in principle a more direct means to probe the role of brain oscillations in cognition: a strictly periodically alternating current is applied to modify brain rhythms directly that have been previously implicated with cognitive function. This way, different parameters of brain oscillations (e.g., amplitude, phase, frequency) become the independent variable and behavioral measures the dependent variable, which in turn allows for causal interpretations. TACS targeting different frequency bands and brain functions has been shown to influence behavioral performance. Alpha tACS phase influences detection of near threshold stimuli in a phasic manner (Neuling et al, 2012a), while the IAF can be modulated by tACS, which in turn affects the multisensory double flash illusion (Cecere et al, 2015)

Objectives

Methods

Conclusion