Investigating nociceptive neural responses during focused hypnotic analgesia: local and remote effects

Hypnoanalgesia is used in several clinical contexts to improve pain management et patient comfort, however, its underlying mechanisms are still unclear. Previous research has demonstrated that hypnoanalgesia can selectively modulate pain perception on a specific body area, a technique known as focused hypnotic analgesia (FHA). The present study aimed to further investigate whether this selective modulation already takes place at a cortical level, or reflects later cognitive processes. Contact heat stimuli were randomly applied to the right and left arms of 30 healthy participants before, during and after suggestion of FHA targeting one arm. Participants rated their perceived intensity after each stimulus, while nociceptive evoked-related potentials (N1, N2, P2 and peak-to-peak N2-P2) were recorded. Results show a behavioural modulation, with reduced perceived intensity for stimuli delivered on the protected arm during FHA as compared to pre- and post-hypnosis conditions. A reduction was also observed for the unprotected arm, although in a lesser extent. These effects varied according to the hypnotisability level of participants, with high hypnotizable participants exhibiting greater analgesic responses than medium and low hypnotizable individuals. No corresponding modulation was observed at the cortical level. However, we unexpectedly observed the N2 peak latency to be earlier for the protected arm compared to the unprotected one in HH during FHA. Together, these findings indicate that FHA selectively modulates perceived intensity in response to nociceptive stimuli depending on its location on the body, but does not alter nociceptive cortical processing.