The effect of heart rate variability biofeedback on cortical arousal and its subsequent influence on vigilance: a randomized controlled study

Heart rate variability biofeedback (HRVBF) has been investigated as a breathing-based intervention to enhance cognitive function, yet its efficacy varies across studies. Understanding the mechanisms underlying this variability is essential for optimizing HRVBF protocols. This study examined the effects of HRVBF and the relationship between cortical arousal and vigilance using multimodal assessments. Fifty-one healthy young adults were randomly assigned to HRVBF (n = 25) or an active control group (n = 26). Participants completed 15-min HRVBF or control breathing with pre- and post-assessments of physiological (heart rate variability, electroencephalography), behavioral (sustained attention to response task), and subjective arousal measures. The results indicated that the HRVBF group had no significant effects on any outcomes compared to the control group. Both groups showed increased root mean square of successive differences, N2 event-related potential Go amplitudes, commission error rates, and subjective arousal, along with decreased N2 No-Go amplitudes and reaction times. Polynomial regression revealed a significant quadratic relationship between changes in alpha band power and commission error rates in the HRVBF group (R² = 0.276, p = 0.029), whereas no significant relationship was found in controls. Although HRVBF did not outperform control breathing, the quadratic association between cortical arousal and vigilance suggests that HRVBF may regulate arousal toward optimal levels. This inverted U-shaped pattern may help explain variability in HRVBF efficacy and highlights the importance of considering non-linear arousal–vigilance dynamics in future research Trial Registration: UMIN-CTR UMIN000058098 (June 5, 2025). https://center6.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000066395