International Handbook of Clinical Hypnosis - E-Lib FK UWKS

68 INTERNATIONAL HANDBOOK OF CLINICAL HYPNOSIS
evoked potentials in response to painful trigeminal nerve stimulation to have
several generators: bilaterally in the secondary somatosensory areas of the trigeminal
nerve system, in the frontal cortex probably related to attention and arousal
processes & in a more central region e.g., cingular gyrus) probably associated with
perceptual activation and cognitive information processing.
Our ®rst fMRI research Downs et al., 1998) using stimulation of the left middle
®nger with a painful electrical stimulation found all participants showed activation
of primary somatosensory S1 either unilaterally or bilaterally, supplementary motor
area bilaterally and primary motor area bilaterally or right only.Posterocentral
activation occurred inconsistently.Unilateral or bilateral activation occurred in
superior and inferior parietal areas, precuneus and dorsolateral frontal cortex.
Frontal pole activation was visible in some.All showed unilateral or bilateral
activation in the cingulate cortex, although speci®c areas differed.Anterior and/or
posterior insular, as well as thalamic, activity was observed in some participants.
Thus, like prior research, we found a widespread neuronal network involving
evaluative and sensory-discriminative pain was activated.
The anterior frontal cortex is known to gate or inhibit somatosensory input,
operating at early stages of sensory processing on both cortical and subcortical
structures, from `the periphery through dorsal column nuclei and thalamus to the
sensory cortex' Yamaguchi & Knight, 1990, p.281).Thus, the frontal region is a
prime candidate to become involved during disattention and active inhibition of
pain during successful hypnotic analgesia.Studies of dynamic changes in regional
cerebral blood ¯ow, EEG activity, somatosensory event-related potentials and even
peripheral re¯exes during hypnotic analgesia lend credence to the hypothesis that
the frontal attention system is actively involved in the inhibition of incoming
somatosensory information coming from the pain source during hypnotic analgesia
and works by way of its connections with the thalamus and possibly other brain
structures to regulate the perception of the intensity of pain e.g., Crawford,
1994a,b; Crawford, Gur et al., 1993; Crawford, Knebel et al., 1996, 1997).
Using the 133-xenon inhalation method during attention and hypnotic analgesia
to ischemic pain applied to the arms, Crawford, Gur et al.1993) found different
rCBF activation patterns in low and high hypnotizable subjects.Using the subtractive
technique, only highs showed further substantial increases in rCBF in the
anterior frontal orbito-frontal and somatosensory regions during successful hypnotic
analgesia.This was interpreted as being supportive of the view that hypnotic
analgesia involves the supervisory, attentional control system Hilgard, 1986) of the
anterior frontal cortex in a topographically speci®c inhibitory feedback circuit that
cooperates in the regulation of thalamocortical activities e.g., Birbaumer, Elbert,
Canavan & Rockstroh, 1990).It also suggests that mental effort occurred during
the inhibition of painful stimuli.Thus, hypnotic analgesia and dissociation from
pain requires higher cognitive processing and mental effortÐand the involvement
of the frontal attentional system.
Further research employing fMRI, PET and SPECT neuroimaging techniques