Parietal but not temporoparietal alpha-tACS modulates endogenous visuospatial attention

Additionally, we measured offline alpha power immediately before and after tACS using electroencephalography (EEG). The behavioral data revealed an effect of tACS on the endogenous but not exogenous attention bias, with a greater leftward bias during left than right hemispheric stimulation. In line with our hypothesis, this effect was brain area-specific, i.e. present for dorsal parietal but not ventral temporoparietal tACS.

However, contrary to our expectations, there was no effect of ventral temporoparietal tACS on the exogenous visuospatial attention bias. There was no effect of either tACS condition on offline alpha power. The fact that the behavioral tACS effect does not generalize to any lateral posterior tACS montage, renders lateral cutaneous and retinal effects for the spatial attention bias in the dorsal parietal condition unlikely.

Yet the absence of tACS effects on the exogenous attention task suggests that ventral temporoparietal alpha oscillations are not functionally relevant for exogenous visuospatial attention. We discuss the potential implications of this finding in the context of an emerging theory on the role of the ventral temporoparietal node.