Cedric Cannard

Background: The Wim Hof Breathing Method (WHM)—involving controlled hyperventilation interleaved with breath retention—induces acute fluctuations in blood gases and autonomic arousal. However, the concurrent neurophysiological signatures underlying this practice, and how they are shaped by expertise, remain largely uncharacterized. Methods: Seventeen adults (10 Level 2 WHM experts; 7 novices) underwent simultaneous 64-channel EEG, electrodermal activity (EDA), and capnography/oximetry during baseline rest, a standardized WHM breathing bout (~10–12 min), and post-WHM rest. Experts additionally completed a brief, eyes-closed cold-water immersion. We analyzed scalp power, source-level beamforming, and multivariate functional connectivity (FC) across phases using cluster-based permutation testing. Results: WHM induced a physiologically aroused yet internally directed cortical state. Across the whole group, WHM drove widespread increases in beta and gamma spectral power. However, EEG results revealed that expertise profoundly shaped network organization. Experts exhibited structured, posterior-dominant dynamics, characterized by left lateral occipital alpha suppression (focal disinhibition), right precuneus beta enhancement, and robust high-gamma power in the precuneus and paracentral somatosensory regions. FC analyses showed that experts established theta-band coupling across sensorimotor–salience hubs and high-gamma connectivity linking the posterior Default Mode Network (DMN) to the anterior cingulate cortex (ACC) and lateral prefrontal cortex. In contrast, novices showed frontopolar gamma increases and beta-band DMN–visual coupling, suggesting a more effortful, externally guided, sensory-mnemonic processing state. During cold immersion, experts further amplified alpha and gamma FC, driving enhanced posterior-to-frontal and somatosensory-visual integration under thermal stress. Physiologically, WHM concurrently drove robust sympathetic activation (increased phasic EDA and tachycardia) and marked hypocapnia. While both groups experienced CO₂ washout, experts achieved significantly deeper hypocapnia (EtCO₂ ~2.54% vs. 3.48% in novices) with steadier respiratory rates, indicating more efficient ventilatory regulation. Conclusions: WHM acutely couples strong sympathetic and hypocapnic arousal with a highly organized, internally focused brain state. Expertise facilitates a shift from novice-like effortful sensory processing to efficient, top-down regulated interoceptive precision, marked by gamma-band integration across DMN, salience, and frontal control networks. These findings provide the first systematic multimodal characterization of WHM's neurophysiological reconfiguration.