Breath-Modulated Biofeedback Loops for Enhancing Autonomic Regulation and Executive Functions through fNIRS and ECG

Breathing is increasingly recognized as a dynamic regulator of autonomic and cognitive systems, yet its integrated impact on cardiac vagal tone, prefrontal hemodynamics, and executive functions remains poorly understood. Here, we introduce a multimodal biofeedback paradigm—combining electrocardiography (ECG), functional near‑infrared spectroscopy (fNIRS), and behavioral cognitive assays—to test how two contrasting yogic breathing techniques acutely modulate the “breath–ANS–PFC–EF” loop in healthy adults (n = 20). Participants performed either Right‑Nostril Yogic Breathing (RNYB; 4-6 breaths min⁻¹) or Bhastrika Pranayama (90-120 breaths min⁻¹) for 5 minutes, following baseline spontaneous breathing. Relative to baseline, Bhastrika (n=9) significantly decreased median interbeat interval (Δ ≈ –20 ms), during breathing, t(8)=7.62, p<0.001, indicating sympathetic activation, whereas RNYB (n=8) selectively increased IBI variance by ~30%, t(8)=–3.55, p=0.008, reflecting enhanced vagal tone. Concurrent fNIRS revealed that RNYB elevated oxyhemoglobin concentration in the right‑lateral prefrontal cortex (median Δ ≈ +0.15 µM; p =0.021), with peak activation exceeding that of Bhastrika (p = 0.034). Behaviorally, RNYB reduced Stroop interference by ~15% (p = 0.029) and improved 2‑back accuracy by ~8% (p < 0.05), whereas Bhastrika yielded faster but less accurate responses. Crucially, across participants, increases in HRV correlated with right‑lateral PFC HbO (ρ ≈ 0.6; p < 0.05) and predicted lower Stroop interference (ρ ≈ –0.5; p < 0.05). These findings demonstrate that volitional respiration can be harnessed to tune an integrated autonomic–cortical–executive control feedback network, offering a blueprint for noninvasive interventions in stress, cognitive aging, cardiovascular and neuropsychiatric disorders.