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

Published: 10 February 2026| Version 1 | DOI: 10.17632/sh76m2vgbc.1
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Description

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.

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1. Participants Fourteen healthy adults (18–30 years, right-handed, normal or corrected vision, no neurological or psychiatric history) participated after written informed consent. The protocol was approved by the local ethics committee (Lorraine University) and conducted in accordance with the general ethical principles of the Declaration of Helsinki (2013) . 2. Experimental design Each participant completed three consecutive phases: • Phase 1: pre-stimulation sham (baseline) • Phase 2: active tDCS • Phase 3: post-stimulation sham In each phase, participants performed identical 10-minute visual stimulation blocks. 3. Fast periodic visual stimulation (FPVS) Unfamiliar face images were presented on a 27-inch LCD monitor (60 Hz, 1280×1024, viewing distance 80 cm). Faces appeared at 6 Hz (one image every 166.66 ms). Every fifth image was a different identity, generating a 1.2 Hz oddball frequency indexing face identity discrimination. Each sequence lasted 71 s (85 cycles). Face size varied (74–120%) and contrast was sinusoidally modulated. Participants maintained fixation and pressed a key when the fixation cross briefly changed color to ensure attention. 4. tDCS protocol tDCS was delivered using a Soterix MxN-9 HD stimulator with two HD-ring electrodes (4.52 cm²). Anode: P10 (right occipito-temporal cortex) Cathode: FT9 (left fronto-temporal cortex) Intensity: 2 mA (~0.44 mA/cm²). Active stimulation lasted 20 min (10 min before and 10 min during FPVS). Sham consisted of 30 s ramp-up and ramp-down. Electrode impedance was ≤10 kΩ. 5. EEG recording EEG was recorded using a Biosemi ActiveTwo system (64 Ag/AgCl electrodes, extended 10–20 system), sampled at 512 Hz (24-bit). EOG channels monitored eye movements. 6. Preprocessing Data were processed with Letswave 6.0 (MATLAB): • 0.1–100 Hz filtering • 50 Hz notch filtering (and harmonics) • Downsampling to 256 Hz • Segmentation by sequence • ICA blink correction when needed • Interpolation of noisy channels (<5%) • Average reference 7. Frequency analysis After removing fade-in/out periods, 71-s epochs were averaged and Fast Fourier Transform applied. Responses were extracted at: • Face-selective frequency: 1.2 Hz and harmonics • Base visual frequency: 6 Hz and harmonics 8. Shared measures For each participant, electrode and phase (before, during, and after tDCS), we provide: - Baseline-corrected amplitude (µV) for face-selective responses (1.2Hz + harmonics) ; upright faces condition - Baseline-corrected amplitude (µV) for face-selective responses (1.2Hz + harmonics) ; inverted faces condition - Baseline-corrected amplitude (µV) for base visual responses (6Hz + harmonics) The dataset contains electrode-level frequency-tagged EEG measures allowing replication of the neuromodulation analysis without raw EEG data.

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Neuromodulation, Electroencephalography, Transcranial Direct Current Stimulation, Cognitive Neuroscience

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