Hypocapnia, Autonomic Signatures, and Gamma-Band Reconfiguration During Wim Hof Breathing Method and Cold Immersion: A comparative study between naive and Level 2 experts

Background: The Wim Hof Breathing Method (WHM), which involves controlled hyperventilation interleaved with breath retention, has been proposed to modulate interoception and autonomic tone; however, neural signatures in trained versus naïve practitioners remain incompletely characterised.Methods: Seventeen adults (10 Level 2 WHM experts; 7 novices) completed eyes closed baseline rest, a standardised WHM bout (~10-12 min; three rounds of nasal power breaths with a low lung volume retention and a recovery inhalation), and post WHM rest; experts also underwent brief eyes closed cold water immersion.A 64-channel EEG dataset was acquired.Spectral power, source-level beamforming, and multivariate functional connectivity were compared across phases using cluster-based permutation testing.End tidal CO₂ (EtCO₂), SpO₂, heart rate, respiratory rate and autonomous activity were monitored.Results: Compared to baseline, WHM yielded distinct patterns.Experts: scalp-frontopolar delta, left-posterior low-beta, strong posterior gamma; source-left superior temporal delta, left lateral occipital alpha suppression, right precuneus beta, left precuneus/right paracentral highgamma; connectivity-theta in sensorimotor-salience hubs and gamma linking posterior DMN to ACC/lateral PFC; physiology-deeper hypocapnia (~2.54%EtCO₂), steadier RR (~10.1/min),higher pulse (~76.4 bpm).Novices: scalp-posterior alpha/beta and frontopolar gamma; source-right temporal-pole delta, right parahippocampal alpha, right fusiform beta, left pericalcarine gamma; connectivity-beta DMN-visual and posterior-temporal gamma; physiology-shallower hypocapnia (~3.48%), higher RR (~11.96/min),lower pulse (~69.9 bpm).Conclusions: WHM acutely induces a physiologically aroused yet internally directed cortical state, marked by gamma enhancement and integration across interoceptive-salience-DMN networks, with clear sympathetic activation.Expertise is associated with more organised, posterior-dominant dynamics.