MECHANISMS OF HYPNOTIC ANALGESIA EXPLAINED BY FUNCTIONAL MAGNETIC RESONANCE (fMRI).

Hypnotic-focused analgesia (HFA) was produced in 20 highly hypnotizable subjects receiving nociceptive stimulations while undergoing functional magnetic resonance imaging (fMRI). The fMRI pattern in brain cortex activation while receiving a painful stimulus was recorded both during nonhypnosis and during HFA. The scanning protocol included the acquisition of a T1-weighted structural scan, 4 functional scans, a T2-weighted axial scan, and a fluid attenuated inversion recovery (FLAIR) scan. Total imaging time, including localization and structural image acquisitions, was approximately 60 minutes. Without HFA, the subjects reported subjective presence of pain, and the cortex primary sensory areas S1, S2, and S3 were activated. During HFA, the subjects reported complete absence of subjective pain and S1, S2, and S3 were deactivated. The findings suggest that HFA may prevent painful stimuli from reaching the sensory brain cortex, possibly through a gate-control mechanism.

Hypnosis prevents the cardiovascular response to cold pressor test.

To highlight the effects of hypnotic focused analgesia (HFA), 20 healthy participants underwent a cold pressor test (CPT) in waking basal conditions (WBC) by keeping the right hand in icy water until tolerable (pain tolerance); subjective pain was quantified by visual scale immediately before extracting the hand from water. The test was then repeated while the participants were under hypnosis and underwent HFA suggestions. Cardiovascular parameters were continuously monitored. Pain tolerance was 121.5+/-96.1 sec in WBC and 411.0+/-186.7 sec during HFA (p < 0.0001), and visual rating score 7.75+/-2.29 and 2.45+/-2.98 (p < 0.0001), respectively. CPT-induced increase of total peripheral resistance was non significant during HFA and +21% (p < 0.01) in WBC. HFA therefore reduced both perception and the reflex cardiovascular consequences of pain as well. This indicates that hypnotic analgesia implies a decrease of sensitivity and/or a block of transmission of painful stimuli, with depression of the nervous reflex arc.

Local and systemic vasodilation following hypnotic suggestion of warm tub bathing.

During hypnosis it is easy to induce hallucinations having, for the hypnotized subject, the characteristics and the concreteness of reality. This study was performed to put in evidence the physical effects of hypnotic suggestion of warm tub bathing. 18 volunteers screened for high hypnotizability were studied. They underwent suggestion of forearm in warm water (30 min), suggestion of body in warm water (30 min), and hypnosis without any thermal suggestion (30 min), while blood pressure, heart rate, body temperature, forearm flow and resistance, stroke volume, cardiac index and total peripheral resistance were monitored. During suggestion of forearm in warm water, local vasodilation was recorded, with decrease of forearm resistance (-18%, P<0.01) and increase of forearm blood flow (+43%, P<0.01) like in real local passive warming. During suggestion of whole-body in a warm water tub, there was a systemic vasodilation with decrease of total peripheral resistance (-29%, P<0.01) and increase of cardiac index (+54%, P<0.01), like in real total-body passive warming. Body temperature, arterial blood pressure and heart rate were unchanged. During simple hypnosis (sham procedure) no haemodynamic variations were observed. These results are in keeping with the possibility to induce through hypnotic suggestion of heat a physical pattern that is typical of hyperthermia, even without increase in body temperature.