Objective neural face recognition neuromodulation within a single transcranial direct current stimulation session

Due to considerable technical and methodological challenges, neuromodulatory effects of online and post-stimulation transcranial direct current electrical stimulation (tDCS) on human cognition remain unclear. Here we evaluated these effects of tDCS on a sensitive, objective and reliable neural marker of human face identity recognition. Eighteen participants took part in this combined tDCS-EEG study. Following a sham tDCS period during rapid periodic individuation of pictures of unfamiliar faces (Phase 1), tDCS was applied for 10 min during the same visual stimulation over the right occipito-temporal cortex (Phase 2), followed by a second sham tDCS period (Phase 3). The face individuation neural electroencephalographic (EEG) response confined to small frequency bins (.014 Hz bandwidth) was significantly reduced by 28% during tDCS. After tDCS, a 66% increase compared to during-tDCS level, i.e., 'rebound' effect, was observed. These effects were of equal magnitude over occipito-temporal regions of the two hemispheres and only limited to neural face individuation, with general neural responses to the global periodic visual stimuli being unaffected. Overall, these observations demonstrate significant and selective neuromodulation of a key human cognitive brain function using a single tDCS session and only two HD-ring electrodes, highlighting the interest of frequency-tagged electrophysiology to quantify neuromodulation effects.