Occipital tACS does not modulate manual performance but fixation variability under visuo-proprioceptive conflict - Neurophysiology

The modulation of oscillations at alpha and beta frequency ranges recorded over sensory cortices has been linked to the top-down weighting of sensory information relative to (competing) information from other modalities. Here, using a virtual reality-based hand-target matching task under visuo-proprioceptive conflict, we tested whether alpha-/beta-tACS over the occipital cortex would improve action performance when conflicting visual movement feedback needed to be ignored in favor of proprioception. Participants had to match a target rhythm with either their unseen real hand (RH) grasping movements, or with the movements of a virtual hand (VH) that displayed their actual movements after a constant time delay. Visual movement feedback was, consequently, either task-relevant (VH task) or a distractor (RH task). In a cross-over, double-blind, within-subject design, we applied either low-intensity (2 mA peak-to-peak) transcranial alternating current stimulation (tACS) at 10 Hz (“alpha”) or 20 Hz (“beta”), or sham, over the occipital cortex during this task. Neither alpha- nor beta-tACS significantly affected hand-target matching performance, but fixation variability in the RH condition significantly decreased during beta-tACS relative to sham stimulation. Thus, despite not directly modulating manual performance, occipital beta-tACS could have facilitated ignoring the mismatching (distracting) visual movement feedback when needed.

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