Transcranial direct current stimulation of the occipitotemporal cortex enhances identification of ambiguous faces

Transcranial direct current stimulation (tDCS) has emerged as a promising tool for investigating the neural mechanisms underlying various brain functions and for enhancing related behavioral performance. In this sham-controlled, between-subjects study, we examined the effects of tDCS applied to the right and left occipitotemporal cortex (OTC) on face identification performance using a delayed match-to-sample task with morphed face images of varying discrimination difficulty. Three active montages were tested: (M1) anode on the right OTC and cathode on the left OTC, (M2) anode on the left OTC and cathode on the right OTC, and (M3) anode on the right OTC with the cathode on the left shoulder. A total of 47 participants were randomly assigned to one of four groups: M1 (n = 13), M2 (n = 12), M3 (n = 13), and Sham (n = 9). The results showed a significant improvement in face discrimination performance with the M1 montage relative to the sham condition. Although performance also improved in M2 and M3, these effects were not significantly different from the sham group. Across all montages, the largest impact on non-match discrimination was observed under more ambiguous conditions, particularly at a 30% morph distance, which corresponded to the point of subjective equality. Furthermore, tDCS stimulation led to longer reaction times across all montages, with the significant delays noted in M1 and M3. Findings of this preliminary study suggest a hemispheric laterality bias in face identity discrimination following tDCS-induced neural modulation.