Neural Mechanisms of Hypnotic Analgesia

Abstract

There is increasing evidence demonstrating that hypnosis could be effective in the down-modulation of pain sensation in both acute and chronic pain states. In the neurophysiological context, recent evidence has deciphered, to a certain extent, the mystery of pain relief upon hypnosis. It is probable that hypnotic suggestions of analgesia are able to modulate pain processing at multiple levels and sites within the central nervous system (CNS). At the peripheral level, hypnosis may modulate the nociceptive input through the down-regulation of the stimulation of A delta and C fibers and reduction of sympathetic arousal. At the spinal level, sensory analgesia occurring during hypnosis has been demonstrated to be linearly associated with the reduction in the nociceptive flexion (RIII) reflex, a polysynaptic spinal reflex. At the supraspinal cortical level, neuro-imaging and electrophysiological studies have demonstrated that hypnotic suggestions of analgesia could directly modulate both sensory and affective dimensions of pain perception, and the affective dimensions exhibit more significant reduction compared to the sensory ones. Moreover, highly hypnotizable subjects possess stronger attentional filtering abilities in comparison to the low hypnotizable subjects; this greater cognitive flexibility of the former might result in better focusing and diverting the attention from the nociceptive stimulus as well as in better ignoring of the irrelevant stimuli in the environment. Cognitive control processes are associated with a “supervisory attentional system” which involves fronto-temporal limbic cortices. Multiple hierarchical pain control systems functioning during hypnotic suggestions of analgesia, demonstrating specific patterns of peripheral and central activation associated with the hypnotic state and with the processing of hypnotic suggestions, provide a novel description of the neurobiological basis of hypnotic analgesia.