Anodal Transcranial Direct Current Stimulation (tDCS) via the Fp3–Fp2 Montage Disrupts Face Recognition Skills

Abstract Over the past fifteen years, transcranial direct current stimulation (tDCS) has been used to modulate face recognition skills. One influential line of work has shown that anodal stimulation delivered with the anode at Fp3, a site overlying the left dorsolateral prefrontal cortex (DLPFC), and the return/cathode at Fp2 reduces the face inversion effect (FIE) by selectively disrupting recognition of upright faces, an effect interpreted as the disruption of perceptual learning. A recurring limitation is that the behavioural paradigms employed have relied on stimulus recognition rather than face identity recognition, because the same images were shown at study and test. It therefore remains unclear whether this procedure modulates face identity recognition or merely image-level recognition. Here we addressed this by applying the tDCS procedure during upright and inverted versions of the Cambridge Face Memory Test (CFMT), a robust identity-recognition paradigm in which learned identities must be recognised across novel images varying in viewpoint, lighting, and noise. Participants (N=64) were randomly assigned in a double-blind, between-subjects design to anodal or sham/control tDCS. A robust FIE was obtained overall, and it was significantly reduced in the anodal group relative to sham. Critically, this reduction was driven by impaired recognition of upright faces under anodal stimulation, with no difference between groups for inverted faces. These results extend the modulation of the FIE from image to face identity recognition, demonstrating that anodal stimulation, via the Fp3–Fp2 montage, disrupts face recognition skills indexed by one of the most widely used tests of face-recognition ability.