Objective Neural Face Recognition Neuromodulation within a Single Transcranial Direct Current Stimulation Session

Because of substantial technical and methodological difficulties, the cognitive neuromodulatory impact of transcranial direct current stimulation (tDCS), both during and after stimulation, is still uncertain in humans. In this study, we examined these effects using a sensitive, objective, and reliable neural indicator of face identity recognition. Participants first underwent a sham tDCS condition while rapidly individuating images of unfamiliar faces (Phase 1). tDCS was then delivered for 10 minutes over the right occipito-temporal cortex during the same visual stimulation (Phase 2), followed by another sham stimulation period (Phase 3). The electroencephalographic (EEG) response associated with face individuation, confined to narrow frequency bins (0.014 Hz bandwidth), decreased significantly by 28% during tDCS. After stimulation, the response increased by 66% relative to the during-tDCS level, indicating a rebound effect. These changes were comparable in magnitude across occipito-temporal areas of both hemispheres and were specific to face individuation, while broader neural responses to the periodic visual stimulation remained unchanged. Taken together, these findings provide evidence of a significant and selective modulation of an essential human cognitive function following a single tDCS session using only two HD-ring electrodes, and they emphasize the usefulness of frequency-tagged electrophysiology for quantifying neuromodulation effects.