Selective Modulation of Interhemispheric Functional Connectivity by HD-tACS Shapes Perception
Figure 4
Modulation of interhemispheric coherence during stimulation.
(A) Grand mean coherence average over four posterior channel pairs: The solid black line depicts average coherence during sham (mean ± SEM). Notch filtering in the γ1-band was applied to all conditions (dark-grey shaded, estimates were obtained after spectral smoothing and not used for statistical analyses; dashed box highlights utilized frequency bands). Dashed lines indicate vertical motion percepts; solid lines depict horizontal percepts. See also Data S1. (B) Relative γ2/3-coherence increase during the horizontal percept (with respect to the vertical percept) revealed that the binding-related coherence increase was still present during tACS (same conventions as in Figure 2C). (C) Absolute γ2/3-power values indicated that coherence changes were not related to gamma-power changes. (D) Coherence change over time (pair of interest). The black dashed line indicated the mean sham value. See also Data S1. (E) Spatial distribution for the coherence modulation. Upper left: In-phase stimulation. Upper right: Anti-phase stimulation. Lower: The Z-score map indicates a significant difference between in- and anti-phasic tACS located over parieto-occipital electrode pairs. Dots highlight the significant cluster. (F) Cluster-based permuted correlation analysis: A baseline corrected motion index (MI) = (MRInPhase − MRShamIn) − (MRAntiPhase − MRShamAnti) was correlated with the baseline corrected ΔCoherence of γ2-coherence values (CohIn-Phase − CohAnti-Phase). Upper panel: The black dots in the topography depict the significant cluster (p = 0.008). Lower panel: Regression line fitted through the mean coherence values as obtained from the cluster test. Dots depict individual subjects. Solid red line depicts the linear regression. (G) Cluster-based permuted correlation analysis indicated that subjects with an individual gamma coherence peak close to the stimulation frequency (40 Hz) exhibit the largest coherence modulation (p = 0.049). (H) Mean gamma power change over time (Data S1). (I) Source reconstruction of gamma activity during in- (green) and anti-phase (orange) stimulation as compared to baseline.