Investigating Cerebral and Systemic Haemodynamics During Hypnosis with Time-Domain Optical Imaging

Clinical hypnosis can relieve pain and anxiety, yet its cerebral and systemic physiological mechanisms remain unclear. Portable optical imaging offers a means to investigate both, provided systemic vascular changes are distinguished from cortical activity. We tested whether time-domain diffuse optical tomography (TD-DOT), which provides separate superficial and model-assigned intracranial estimates, withstands a challenge from each recording’s own scalp field. In processed continuous-wave near-infrared spectroscopy (NIRS) hypnosis recordings (26 participants), low-frequency oxyhaemoglobin variability decreased by 21.8% (P = 0.0067), whereas a network effect did not survive global-signal regression. In a time-domain NIRS auditory cohort (49 participants, two visits), withheld short channels matched reconstructed scalp more closely than intracranial estimates (t(48) = 16.5). In the auditory cohort, scalp-only injection reproduced an apparent intracranial HbR phase lead, whereas attenuated 0.02–0.07-Hz HbO/HbT transfer differed from the specified leakage null (P < 10⁻⁶). In three exploratory hypnosis sessions (novice, intermediate and experienced participants), heart-rate fluctuations at 0.04–0.15 Hz were lower than during induction in all nine phase comparisons, and directly measured forehead pulsatility increased in two participants. These findings support leakage-aware optical monitoring during hypnosis, while intracranial source identity and hypnosis-specific effects require independent validation.