ABSTRACT

Introduction: Transcutaneous auricular vagus nerve stimulation (taVNS) is an emerging neuromodulation technique showing promise in modulating affective processing. However, comparative evidence between electric and ultrasound modalities remains limited. This study aimed to investigate and compare the acute effects of electrical (E-taVNS) and ultrasound (U-taVNS) modalities on emotional bias in healthy young adults.

Materials and Methods: A total of 59 healthy participants were randomly assigned to E-taVNS or U-taVNS group and completed a single-blind, sham-controlled, within-subject study. Emotional bias was assessed using a facial emotion categorization task using morphed expressions at pre-, during, and post stimulation phases.

Results: Active taVNS significantly enhanced emotional bias scores relative to sham when both stimulation modalities were

pooled (t(58) = 2.09, p = 0.020, d = 0.27), shifting categorization of ambiguous faces toward more positive interpretations. Within

each modality, active stimulation produced significant pre-to-post increases in bias scores, though the active-versus-sham

contrast did not reach statistical significance for either modality individually (E-taVNS: p = 0.107; U-taVNS: p = 0.063, one-

tailed). No significant between-modality differences were detected. In addition, individual differences in interoceptive awareness correlated with treatment response magnitude.

Conclusions: When pooled, active electric and ultrasound taVNS acutely modulated emotional bias relative to sham stimulation.

These findings support taVNS as a promising noninvasive, well-tolerated intervention for research on emotional bias, with potential for further investigation of personalized treatment based on interoceptive awareness.

Keywords: Electrical stimulation, emotional bias, transcutaneous auricular vagus nerve stimulation, ultrasound