Date Published: November 22, 2013
Publisher: Public Library of Science
Author(s): Vilfredo De Pascalis, Emanuela Russo, Ryouhei Ishii.
A working model of the neurophysiology of hypnosis suggests that highly hypnotizable individuals (HHs) have more effective frontal attentional systems implementing control, monitoring performance, and inhibiting unwanted stimuli from conscious awareness, than low hypnotizable individuals (LHs). Recent studies, using prepulse inhibition (PPI) of the auditory startle reflex (ASR), suggest that HHs, in the waking condition, may show reduced sensory gating although they may selectively attend and disattend different stimuli. Using a within subject design and a strict subject selection procedure, in waking and hypnosis conditions we tested whether HHs compared to LHs showed a significantly lower inhibition of the ASR and startle-related brain activity in both time and intracerebral source localization domains. HHs, as compared to LH participants, exhibited (a) longer latency of the eyeblink startle reflex, (b) reduced N100 responses to startle stimuli, and (c) higher PPI of eyeblink startle and of the P200 and P300 waves. Hypnosis yielded smaller N100 waves to startle stimuli and greater PPI of this component than in the waking condition. sLORETA analysis revealed that, for the N100 (107 msec) elicited during startle trials, HHs had a smaller activation in the left parietal lobe (BA2/40) than LHs. Auditory pulses of pulse-with prepulse trials in HHs yielded less activity of the P300 (280 msec) wave than LHs, in the cingulate and posterior cingulate gyrus (BA23/31). The present results, on the whole, are in the opposite direction to PPI findings on hypnotizability previously reported in the literature. These results provide support to the neuropsychophysiological model that HHs have more effective sensory integration and gating (or filtering) of irrelevant stimuli than LHs.
Hypnotizability, generally defined as the ability to enter a hypnotic state, is a complex behavioural phenomenon with biological, cognitive and social components. Hypnosis requires an individual to mainly attend the hypnotist’s voice while disattending/ignoring distracting thoughts and stimuli. Accordingly, there is a broad consensus in considering hypnotic susceptibility as an individual characteristic closely related to the ability to focus and sustain attention on relevant stimuli and to shut-off irrelevant ones , . A number of studies have demonstrated a more effective frontal attentional control system in high hypnotizable (HH) individuals than low hypnotizable (LH) individuals –. The HHs, as compared to LH individuals, typically demonstrate faster reaction times during complex decision-making tasks – and shorter peak latencies for auditory, visual, and somatosensory components of the event-related potential (ERP) –. While the neurobiological substrates of hypnosis have not been resolved, recent findings indicate that the attentional skills involved in hypnotizability may correlate with central dopaminergic activity , .