Nabhi Science as a Non-Pharmacological Modality for Stress Reduction: Vagal Modulation and Cortisol Balance

Background: Emotional regulation, the capacity to modulate emotional responses in adaptive ways, is funda-mentally underpinned by autonomic nervous system (ANS) balance - specifically vagal tone. Heart rate variabil-ity (HRV) has emerged as the most widely validated non-invasive biomarker of vagal modulation and autonomic flexibility. Nabhi (umbilical) stimulation, practised as Nabhi Chikitsa in Ayurveda and Shenque (CV8) therapy in Traditional Chinese Medicine (TCM), is increasingly proposed as a non-pharmacological neuromodulatory intervention, yet its neurophysiological mechanisms remain underexplored. Objective: To review and synthesise the available neurophysiological, autonomic, and traditional medicine evi-dence relevant to the proposed correlation between Nabhi stimulation and emotional regulation, with specific emphasis on vagal modulation mechanisms, HRV indices, and limbic-prefrontal regulatory pathways; and to propose a rigorously designed experimental framework for HRV-based and neuroimaging validation of this cor-relation. Methods: A structured narrative synthesis was conducted of peer-reviewed literature from PubMed, Scopus, Web of Science, IndMED, and DHARA (an Ayurvedic literature database) published through December 2024. Search terms included: Nabhi stimulation, Shenque CV8, HRV emotional regulation, vagus nerve emotion, neu-rovisceral integration, polyvagal theory, abdominal somato-visceral reflexes, interoception emotion, acupuncture autonomic, Ayurveda Nabhi Chikitsa, prefrontal limbic HRV, and RMSSD anxiety depression. Mechanistic cor-relations are constructed from convergent evidence streams, and a prospective experimental framework is out-lined. Results: Evidence from vagal neurobiology, HRV-emotion meta-analyses, abdominal somatosensory stimulation studies, and CV8/Shenque acupuncture research converges to support a plausible mechanistic pathway by which Nabhi stimulation may enhance emotional regulation. The proposed pathway proceeds through: (1) activation of abdominal vagal afferents at the T10 dermatome; (2) modulation of the nucleus tractus solitarius (NTS) and dor-sal motor nucleus of the vagus (DMNV); (3) increased parasympathetic cardiac output and elevated HRV (RMSSD, HF-HRV); and (4) improved prefrontal inhibitory control over limbic reactivity through neurovisceral integration. Polyvagal theory provides an additional framework through which Nabhi stimulation may facilitate state transition from sympathetic mobilisation to ventral vagal social engagement. Key HRV metrics (RMSSD, HF-HRV, LF/HF ratio) are identified as primary outcome candidates, with frontal EEG alpha asymmetry and amygdala-PFC functional connectivity as exploratory neuroimaging endpoints. Conclusion: Converging evidence from neurophysiological, autonomic, and traditional medicine supports a the-oretically coherent and pharmacologically plausible correlation between Nabhi stimulation and enhanced emo-tional regulation via vagal modulation pathways. This review provides the first comprehensive mechanistic syn-thesis of this hypothesis and proposes a CONSORT-compliant, HRV- and EEG-based randomised crossover study design to establish causality. Translation of this hypothesis into rigorous clinical evidence would support the integration of Nabhi Chikitsa into non-pharmacological protocols for anxiety, depression, and stress-related emotional dysregulation.