Simultaneous prefrontal-occipital high-definition transcranial direct-current stimulation modulates beta and gamma...

Recent studies have shown that prefrontal, parietal, and occipital cortices are critical for abstract reasoning and other fluid intelligence tasks, although the contribution of individual regions and possible laterality effects remain poorly understood. Herein, we use an innovative dual-montage, high-definition transcranial direct-current stimulation (HD-tDCS) approach to examine the impact of simultaneously stimulating prefrontal and occipital cortices on the neural oscillatory dynamics underlying abstract reasoning in 44 healthy adults. Across three sessions, participants underwent concurrent anodal stimulation of the midline occipital and either left or right dorsolateral prefrontal cortices (DLPFC), or sham to both sites. Participants then completed an abstract reasoning task during magnetoencephalography (MEG) and the resulting data were imaged in the time-frequency domain and examined voxel-wise using 1 × 3 repeated-measures ANOVAs. Significant stimulation-related effects included stronger beta oscillations (i.e., more negative relative to baseline) in the left DLPFC following right DLPFC-occipital HD-tDCS relative to both left DLPFC-occipital stimulation and sham. Stronger beta oscillations were also found in the right temporoparietal junction (TPJ) following either type of active stimulation relative to sham. Additionally, we found increased gamma activity in the left inferior parietal, left supplementary motor area, and left somatosensory cortices following both types of active stimulation relative to sham, and the strength of such gamma activity was significantly related to reaction time. In conclusion, we found that anodal stimulation of the DLPFC-occipital cortices strengthened beta and gamma oscillations in key regions for abstract reasoning, with some evidence for laterality effects on prefrontal stimulation and implications for behavior.