Effects of slow oscillatory HD-tDCS on creative cognition and prefrontal cortex activity: A multimodal EEG-fNIRS study

Creativity relies on the dynamic interaction between the default mode (DMN) and frontoparietal control (FPCN) networks, supported by controlled attentional processing and associative strategies. Slow wave activity (SWA: 0.1- 1 Hz) is a critical component of network reorganization during non-REM sleep; while slow oscillatory tDCS (so-tDCS) at 0.75 Hz has been shown to acutely modulate SWA to enhance cognition. This study employed a novel concurrent EEG-fNIRS multimodal imaging approach to investigate whether so-tDCS at 0.75 Hz over the bilateral dorsolateral prefrontal cortex (DLPFC) and medial prefrontal cortex (mPFC) modulates brain oscillations and haemodynamics to promote creativity. Participants (N = 39) completed the Unusual Uses and Picture Completion (PC) creative tasks while receiving sham/so-tDCS at 0.75 Hz using a 2 × 1 high-definition (HD) montage with two anodes (F3, F4) and one cathode (Fpz) for 30 min in a double-blind, sham-controlled, crossover experiment. Compared to sham, so-tDCS significantly increased originality in PC (p = .014, g = 0.40) and was accompanied by sustained increases in oxygenation in the left prefrontal cortex (PFC, p = .003). Post-stimulation, functional connectivity (FC) within left PFC was increased and within right was reduced, accompanied by significantly lower SWA in the left PFC. In addition, asymmetrical fNIRS-derived FC patterns were observed: higher left intrahemispheric PFC (p = .007), and lower interhemispheric PFC (p = .015). These findings suggest that so-tDCS using a HD montage over the bilateral DLPFC and mPFC enhances visual creativity by dynamically adjusting the left PFC resources, which subsequently may trigger downscaling mechanisms.