Brain Activity and Functional Connectivity Associated with Hypnosis

Abstract

Hypnosis has proven clinical utility, yet changes in brain activity underlying the hypnotic state have not yet been fully identified. Previous research suggests that hypnosis is associated with decreased default mode network (DMN) activity and that high hypnotizability is associated with greater functional connectivity between the executive control network (ECN) and the salience network (SN). We used functional magnetic resonance imaging to investigate activity and functional connectivity among these three networks in hypnosis. We selected 57 of 545 healthy subjects with very high or low hypnotizability using two hypnotizability scales. All subjects underwent four conditions in the scanner: rest, memory retrieval, and two different hypnosis experiences guided by standard pre-recorded instructions in counterbalanced order. Seeds for the ECN, SN, and DMN were left and right dorsolateral prefrontal cortex, dorsal anterior cingulate cortex (dACC), and posterior cingulate cortex (PCC), respectively. During hypnosis there was reduced activity in the dACC, increased functional connectivity between the dorsolateral prefrontal cortex (DLPFC;ECN) and the insula in the SN, and reduced connectivity between the ECN (DLPFC) and the DMN (PCC). These changes in neural activity underlie the focused attention, enhanced somatic and emotional control, and lack of self-consciousness that characterizes hypnosis.

Keywords: brain activity; fMRI; functional connectivity; hypnosis; resting state.

© The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

Figures

Figure 1.

Experimental design. Four scans were performed in counterbalanced order for each subject (hypnosis conditions, rest, memory). All 4 scans were performed within one session, with each scan preceded directly by either instructions (rest, memory scans) or induction (hypnosis scans). Orange bars indicate timing of instruction/induction reminders during each scan, and blue bar indicates within-scan ratings. Subjects provided post-scan ratings immediately following the entire session.

Figure 2.

fALFF activity in the dACC. Group (high vs. low hypnotizable) by condition (rest/memory vs. hypnosis in random order) differences in dACC activity. Images are displayed in radiologic convention: the left side of the image corresponds to the right side of the brain. (A) Group by condition interaction (upper panel): blue regions show an interaction between group (high vs. low) and condition (hypnosis vs. rest). The interaction is N.S. for memory relative to rest at the same threshold. The two hypnosis conditions do not show significantly different fALFF. Mean z scores extracted from significant dACC cluster are plotted across group and condition (right panel). Hypnosis versus rest within highs (lower panel): blue regions confirm significantly decreased fractional amplitude during hypnosis relative to rest only for highs. The effect is not significant for memory relative to rest at the same threshold. (B) Hypnotic response scores correlate with fALFF: blue regions show decreasing fractional amplitude during hypnosis relative to rest as post-scan intensity of hypnosis ratings increases, among all 36 highs. Scatterplot shows individual mean z scores extracted from the significant dACC region against individual mean intensity of hypnosis ratings.

Figure 3.

Group (high vs. low) by condition (hypnosis vs. rest/memory in random order) differences in functional connectivity during hypnosis between left and right DLPFC and ipsilateral insular cortex and contralateral supramarginal gyrus. Seeds displayed in red. (A) Left DLPFC, Group by condition interaction (upper panel): orange–yellow regions show significantly increased functional connectivity to left DLPFC during hypnosis relative to rest, for highs but not lows. The effect is not significant for memory relative to rest at the same threshold. Hypnosis versus rest within highs (lower panel): orange–yellow regions confirm significantly increased FC to left DLPFC during hypnosis relative to rest for highs alone. The effect is not significant for memory relative to rest at the same threshold. The two hypnosis conditions are not significantly different. Mean z scores extracted from significant left insula cluster are displayed across group and condition (right panel). (B) Right DLPFC, Hypnosis versus rest within highs: orange–yellow regions show significantly increased FC to right DLPFC during hypnosis relative to rest for highs alone. Also, regions in the paracingulate gyrus and left insula showed significantly greater connectivity with right DLPFC in highs relative to lows. (C) Hypnotic response scores correlating with FC: orange–yellow regions (insular cortex and supramarginal gyrus) show increased FC to left DLPFC during hypnosis. For PCC and dACC seeds, no regions in the group by condition comparison survived correction, so no further tests were performed.

Figure 4.

Intensity of hypnosis covaries inversely with DLPFC-DMN connectivity: seeds displayed in red. (A and B) Connectivity during the two hypnotic states (averaged across happy/vacation) covaried with mean intensity of hypnosis ratings for 36 highs: regions in blue exhibit decreased FC with left (A) and right (B) DLPFC among subjects who felt more hypnotized. Scatterplots show individual mean z scores extracted from significant PCC clusters against individual mean hypnotic experience ratings.