Single-Session HRV Biofeedback Alters Neural Activity but Not Subjective Anxiety

Anxiety and stress are among the most prevalent mental health concerns worldwide, yet barriers to effective treatment remain high. Biofeedback-based approaches offer a promising, low-cost complement to traditional interventions. The present study examined whether real-time heart rate variability (HRV) biofeedback enhances the efficacy of paced breathing for reducing state anxiety, and whether self-reported and neural measures of anxiety relief converge. Healthy adults completed a speeded Stroop task for stress induction, followed by a ten-minute paced breathing exercise. Participants were randomly assigned to an HRV biofeedback condition, in which real-time cardiac variability was displayed, or a control condition with the same breathing cue and no physiological feedback. State anxiety was assessed using the Spielberger State-Trait Anxiety Inventory (STAI-S), and neural activity was measured via EEG spectral power across delta, theta, alpha, and beta frequency bands. The Stroop task reliably elevated state anxiety, and paced breathing reduced STAI-S scores equivalently in both groups; HRV biofeedback did not confer additional subjective benefit. In contrast, EEG analyses revealed that the biofeedback group showed increases in delta and bilateral theta power relative to controls, and spatially widespread increases in alpha and beta power. Time-frequency analyses further showed more extensive and sustained spectral modulation in the biofeedback condition. These findings reveal a dissociation between self-reported and neural responses to a brief HRV biofeedback intervention: paced breathing alone was sufficient to reduce acute state anxiety, while HRV biofeedback produced distinct changes in neural oscillatory activity without enhancing self-reported anxiety relief. These results show that subjective anxiety recovery and neural recovery can diverge during acute HRV biofeedback, suggesting that physiological engagement with biofeedback emerges before conscious benefits.