The Involvement of Frontally Modulated Attention in Hypnosis and Hypnotic Susceptibility: Cortical Evoked Potential Evidence

The frontal N100 difference wave (N100d) between cortical evoked potentials to frequent and infrequent tones was compared before and during hypnosis in subjects with high and low hypnotic susceptibility (n = 10,11). This was to test putative alterations in attention, novelty detection in particular, modulated by anterior functions including the anterior cingulate to auditory stimuli extraneous to hypnosis. Susceptibility was measured with the HGSHS:A and validated with a laboratory scale during the experiment. Results showed that in the highly susceptible participants the N100d was clearly manifested in the pre-hypnosis control condition, was later attenuated following instructions of hypnosis and was virtually absent after further hypnosis. The effect was due to attenuated responding to the infrequent stimulus, without change to the frequent stimulus. This compromise extended to the later frontal P300 wave whose amplitude was reduced by 50% with hypnosis and was negligible by the end of hypnosis. The parietal P300 was reduced in both hypnosis conditions to a similar degree. These results were consistent with a progressive reduction throughout the hypnotic induction in focused attention to stimuli incidental to hypnosis capable of frontal modulation and frontal activation to the novel stimulus. In contrast the participants with low susceptibility showed an opposite pattern of change in the N100d. Though absent before hypnosis there was a progressive increase in the N100d from the first to the second hypnosis recording. This was underpinned by changes in response amplitudes to both frequent and infrequent stimuli, without systematic changes to the P300. Their results supported a dispersion of attentional resources and an absence of frontal activation in the pre-hypnosis baseline, compatible with a lack of focused attention and engagement of frontal functions theorized to be necessary for hypnosis. Furthermore subjects with low hypnotizability showed a longer P300 latency at the central parietal peak compatible with more prolonged processing of the rare stimulus, in keeping with a more posterior bias in processing. This may militate against the induction of hypnosis, theorized to require initial engagement of anterior processes, and here supported by the results in the highly hypnotizable participants.