P126 Spatiotemporal and task dependence of broadband aftereffects observed following parietal 10-Hz tACS: A MEG study. Issue 3 (March 2017) - Tesche, C.
Abstract : Introduction: Rhythmic tACS is known to entrain brain oscillations. Less well characterized are aftereffects of tACS that may result from stimulation-driven entrainment and/or cross-frequency coupling or more generally from broadband responses determined by intrinsic and/or task-dependent local and brain network properties (Veniero2015 ). Objective: To characterize aftereffects of 10-Hz tACS within multiple cortical and subcortical brain regions. Materials & methods: 10-Hz active (1 mA, 20 min) and sham (1 mA, 30 s) tACS was applied in separate experimental sessions over bilateral parietal cortex (P3/P4) during performance of a visual global/local attention task. Structural MRI/MEG data were obtained from 8 healthy adult participants. Images presented were "global" letters (H or S) composed of smaller, "local" letters (H or S). A visual cue switched motor responses between global and local features. MEG data were cleaned with Elekta Neuromag MaxFilter TM . Brainstorm was used to remove eyeblink and cardiac artifacts and to extract Morlet time–frequency (TF) waveforms for brain regions in the Desikan-Killany atlas. Power TF plots were averaged across participants and compared (active vs. sham, t -test p 0.05) for a subset of 1612 sham/active global/local trials recorded ∼5 and ∼10 min post stimulation. Results: Significant increases in alpha and beta were seen in bilateral inferior parietal cortex, with increased left hemisphere gamma for "local" but not "global" trials. Task-related decreased activation at alpha, beta, ∼30 Hz and gamma was observed in left hippocampus for both "local" and "global" trials. Aftereffects were also observed in bilateral superior parietal, superior frontal and lateral occipital cortex as well as medial orbitofrontal cortex, precuneus and cerebellum. Conclusion: We found complex frequency- and task-dependence of oscillatory activity following 10-Hz tACS, supporting the notion that aftereffects are modulated by intrinsic and/or task-dependent local and network properties.