a b s t r a c tThe cold pressor test (CPT) is an empirically validated test commonly used in research on stress, pain and cardiovascular reactivity. Surprisingly, the equivalent test with water heated to noxious temperatures (hot water immersion test, HIT) has not been thoroughly investigated. The aim of the present study was to characterize the physiological effects and psychophysics of both tests and to analyze whether the autonomic responses are mainly induced by baroreflexes or a consequence of the pain experience itself. The study consisted of a single session including one CPT (4 ± 0.2°C) and one HIT (47 ± 0.5°C; cut-off point 5 min) trial performed on 30 healthy drug free volunteers aged 19-57 (median 24) yrs. The sequence of both trials was alternated and participants were randomly assigned to sequence order and parallelized with respect to gender. Physiological parameters (cardiovascular, respiratory and electrodermal activity) and subjective pain intensity were continuously monitored. In addition, pain detection and tolerance thresholds as well as pain unpleasantness were assessed. Both tests were comparable with regard to the time course and intensity of subjective pain. However, a significantly higher increase of blood pressure could be observed during the CPT when compared to the HIT. The HIT appears less confounded with thermoregulatory baroreflex activity and therefore seems to be a more appropriate model for tonic pain.

The feeling of automaticity reported by individuals undergoing a hypnotic procedure is an essential dimension of hypnosis phenomenology. In the present study, healthy participants rated their subjective experience of automaticity and resting-state arterial spin labelling (ASL) scans were acquired before and after a standard hypnotic induction (i.e., perceived automaticity was positively associated with activity in the parietal operculum (PO) and seed-based coactivation analysis revealed additional associations in the anterior part of the supracallosal cingulate cortex (aMCC). This is consistent with the role of these regions in perceived self-agency and volition and demonstrates that these effects can be evidenced at rest, in the absence of overt motor challenges. Future studies should further examine if/how these changes in brain activity associated with automaticity might facilitate the responses to suggestions and contribute to clinical benefits of hypnosis.

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Hot and ice-water immersions are commonly used for heterotopic noxious counter-stimulation (HNCS) in investigations on endogenous pain modulation. However, coincident sympathetic thermoregulatory activity does not allow to differentiate between perceptual hypoalgesia related to baroreflex sensitivity (BRS) or diffuse noxious inhibitory controls (DNIC). The present study analysed the internal validity of another supposedly less confounded tonic pain model (inter-digital web pinching; IWP) regarding its potential as DNIC trigger. We performed a randomized controlled study in 24 healthy gender-matched drug-free volunteers aged 21-54 (median 25) years. The study protocol comprised the assessment of mechanical and thermal perceptual wind-up before and after an IWP (15N) or hot water immersion trial (HIT; 47.5°C) of 2 min duration. Wind-up was induced either by 10 repetitive (1Hz) contact heat (max. 49°C; 5×5 mm thermode) or ballistic impact stimuli (0.5g at 9 m/s) on the phalanges of the non-dominant hand. Cardiovascular activity, pain experience and corrugator muscle activity were continuously monitored. Although both HNCS forms produced a similar pain experience (45% of scale), a more pronounced cardiovascular activity was observable for the HIT (P<0.01). This indicates a higher baroreceptor activity and stronger contamination of painful water immersion by BRS-related hypoalgesia. Regardless of pain modality, wind-up was significantly reduced by HNCS, although this was stronger for painful water immersion than for noxious pinching (P<0.01). The HNCS types allow a differentiation between BRS-related and DNIC-like hypoalgesia. IWP proved its validity for DNIC induction, being practically non-confounded by BRS.