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EEG Correlates of Virtual Reality HypnosisDavid White a; Joseph Ciorciari a; Colin Carbis a; David Liley a

a Swinburne University of Technology, Hawthorn, Melbourne, Australia

Online Publication Date: 01 January 2009

To cite this Article White, David, Ciorciari, Joseph, Carbis, Colin and Liley, David(2009)'EEG Correlates of Virtual RealityHypnosis',International Journal of Clinical and Experimental Hypnosis,57:1,94 — 116

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Intl. Journal of Clinical and Experimental Hypnosis, 57(1): 94–116, 2009Copyright © International Journal of Clinical and Experimental HypnosisISSN: 0020-7144 print / 1744-5183 onlineDOI: 10.1080/00207140802463690

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NHYP0020-71441744-5183Intl. Journal of Clinical and Experimental Hypnosis, Vol. 57, No. 1, Sep 2008: pp. 0–0Intl. Journal of Clinical and Experimental HypnosisEEG CORRELATES OF VIRTUAL REALITY HYPNOSIS

EEG Correlates of Virtual Reality HypnosisDavid White et al.DAVID WHITE, JOSEPH CIORCIARI, COLIN CARBIS, AND DAVID LILEY1

Swinburne University of Technology, Hawthorn, Melbourne, Australia

Abstract: The study investigated hypnosis-related electroencephalo-graphic (EEG) coherence and power spectra changes in high and lowhypnotizables (Stanford Hypnotic Clinical Scale) induced by a virtualreality hypnosis (VRH) induction system. In this study, the EEG from17 participants (Mean age = 21.35, SD = 1.58) were compared basedon their hypnotizability score. The EEG recording associated with a2-minute, eyes-closed baseline state was compared to the EEG duringa hypnosis-related state. This novel induction system was able to pro-duce EEG findings consistent with previous hypnosis literature.Interactions of significance were found with EEG beta coherence. Thehigh susceptibility group (n = 7) showed decreased coherence, whilethe low susceptibility group (n = 10) demonstrated an increase incoherence between medial frontal and lateral left prefrontal sites.Methodological and efficacy issues are discussed.

Two of the central questions associated with psychophysiologicalresearch of hypnosis are whether electrocortical differences exist todistinguish an alert state from a hypnotic state and whether high andlow hypnotizable individuals exhibit contrasting brain functionchange after a hypnotic induction (Ray, 1997). Analysis of electroen-cephalogram (EEG) spectral power and coherence have been impli-cated in distinguishing an alert state from hypnosis and individuals ofhigh and low hypnotic susceptibility. The present study furtheraddressed these findings.

Theoretical ModelsAttentional processes have been implicated in hypnosis (Tellegan &

Atkinson, 1974), with later studies providing further support for a neu-rophysiological model of hypnosis that describes inhibition of frontalattentional processes as central to hypnotic induction (Crawford, 1994;Gruzelier, 1998). According to this model, instruction to focus atten-tion leads to frontal attentional processes being engaged, and thenupon suggestion of relaxation an inhibition of these frontal attentional

Manuscript submitted June 4, 2007; final revision accepted August 29, 2007.1Address correspondence to Dr. Joseph Ciorciari, Brain Sciences Institute, Faculty of

Life & Social Sciences, 400 Burwood Rd. Hawthorn, Swinburne University of Technology,Hawthorn, Melbourne, 3122 Australia. E-mail: jciorciari@swin.edu.au

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EEG CORRELATES OF VIRTUAL REALITY HYPNOSIS 95

processes follows. Finally, the hypnotic state is achieved, and func-tional activity is redistributed depending on the hypnotic suggestion.As part of this model, individuals low in hypnotic susceptibility fail todemonstrate these frontal attentional changes.

The dissociated control model of hypnosis (Bowers, 1992) proposesthat during hypnosis subsystems of control can be automaticallyemployed without being governed by higher executive control medi-ated largely by the frontal lobes (Woody & Sadler, 1998). Neuropsy-chological and psychophysiological empirical support exists for bothmodels.

Frontal Attentional Changes in HypnosisNeuropsychological tests have demonstrated alterations in task per-

formance after hypnosis in high susceptibility groups. Decreased per-formance on a left frontal task (word fluency) in high hypnotizablesafter a hypnotic induction has been reported with no concurrentchanges to right frontal (spatial task) and left temporal (category flu-ency) task performance (Gruzelier & Warren, 1993; Kallio, Revonsuo,Hämäläinen, Markela, & Gruzelier, 2001). This was not observed in thelow hypnotizability group. Decreased performance of high hypnoticsusceptibility groups have been identified on Stroop tasks in the formof increased errors and increased reaction time in several studies(Jamieson & Sheehan, 2004; Kaiser, Barker, Haenschel, Baldeweg, &Gruzelier, 1997; Kallio et al.). This performance can be interpreted asreduced supervisory attentional control in high hypnotizabilitygroups. The suppression of the automatic response and the use of top-down strategy required for successful completion are impacted. Thesefindings support the dissociated control and neurophysiological mod-els of hypnosis in identifying a role for frontal attentional alterations inthe hypnotic experience (Jamieson & Sheehan).

Psychophysiological measures have provided further evidence ofalterations in attention in hypnosis for highly hypnotizable individu-als. Using electrodermal responses, high susceptibility groups exhibitboth a reduction in the orienting response—a measure of focusingattention—and faster habituation in hypnosis, indicative of decreasedattention to a stimulus (Gruzelier, Allison, & Conway, 1988; Gruzelier& Brow, 1985). The opposite results were observed in low susceptibil-ity groups, supporting a role for diminished attentional capacity dur-ing hypnosis in high susceptibility groups. Gruzelier, Gray, and Horn,(2002) exposed high and low susceptibility groups to a frequent andinfrequent tone while recording frontal EEG, focusing on the N100component of the event-related potential (ERP) waveform. The N100difference wave (frequent-infrequent) is generally regarded as havingan attentional component. High hypnotizables demonstrated a largedifference wave at baseline, reducing after relaxed hypnotic induction.

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The low hypnotizability group showed an increased N100 differencewave after hypnotic induction, indicative of increased attentive pro-cesses. This wave discriminated between high and low susceptibilitygroups and highlighted the presence of frontal attentional inhibitionduring hypnosis for high susceptibility groups.

EEG Coherence Studies of HypnosisWith evidence of an inhibition of frontal attentional processes in

hypnosis, EEG coherence has also been used in an attempt to elucidatethe underlying mechanisms through which highly susceptible individ-uals fully experience hypnotic phenomena. EEG coherence is used as ameasure of synchronization between different areas of cortex, wherehigh coherence between sites is interpreted as functional connectivityof those areas (Hogan, Swanwick, Kaiser, Rowan, & Lawlor, 2003).Any alteration in frontal functioning may be evident on such a measure.Egner, Jamieson, and Gruzelier explored frontal attentional processesin hypnosis in a recent event-related Functional Magnetic ResonanceImaging (fMRI) and EEG coherence study (2005). This study used thedeveloping Stroop-task research paradigm to explore conflict process-ing, applying it to changes in response conflict processing associatedwith hypnotic induction. Previous research in the area has implicatedthe anterior cingulate cortex in the process of monitoring conflict causedby different streams of processing such as that initiated by the Strooptask (Botnivick, Cohen, & Carter, 2004; Kerns et al., 2004), while the lateralfrontal cortex has been proposed to exert cognitive control to resolvesuch conflict (MacDonald, Cohen, Stenger, & Carter, 2000).

Egner and colleagues (2005) measured regional cerebral blood flowand electrocortical connectivity in high and low hypnotic susceptibilitygroups during completion of a Stroop task. Participants completed theStroop task during fMRI recording and again during EEG recordings.In both recording sessions, the Stroop task was completed at baselineand then after presentation of an audiotaped hypnotic induction. ThefMRI data showed an increase in anterior cingulate activation in highhypnotizables during hypnosis compared to both baseline and that oflow hypnotizables. This was interpreted as decreased efficiency of con-flict resolution in hypnosis and was not accompanied by an increase incognitive control activation in lateral frontal regions. The EEG coher-ence recordings revealed that the high hypnotizability group showed adecrease in gamma band coherence between a medial frontal electrode(Fz) and lateral electrode placement (F3) in high conflict Stroop trialsduring hypnosis, while low hypnotizables showed an increase. Whencombined, these findings were interpreted as evidence of a functionaldissociation of medial conflict monitoring and lateral cognitive controlprocesses in highly hypnotizable individuals during hypnosis; a trendnot seen in low hypnotizables.

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An unpublished experiment by Kaiser (cited in Gruzelier, 1998,1999) found a significant interaction in the upper alpha frequencyband at a bipolar left frontal lateral electrode pair and a medial pair inhypnosis. High hypnotizables showed a reduction in upper alphaband coherence within these electrode pairs from baseline to hypnosisconditions, while the low hypnotizability group showed an increase inhigh alpha coherence between these electrode pairs. Decreased coher-ence in high hypnotizables was then thought to reflect a reduction insynchronization of left frontal functional processes in hypnosis(Gruzelier, 1998, 1999). Functional connectivity has also been assessedin a case study of a highly hypnotizable individual after a “neutral”hypnotic induction (Fingelkurts, Fingelkurts, Kallio, & Revonsuo,2007). Consistent with the notion of impaired functional connectivity,synchrony between anterior sites was significantly lower across multi-ple frequency bands.

While these findings work to implicate a decrease in functional con-nectivity within left frontal regions in the hypnotic process, the use ofcoherence as a measure of functional connectivity of underlying struc-tures remains controversial. Scalp-recorded EEG coherence can onlyprovide a rough estimate of the locations with which the recordingsare attributed (Ruchkin, 2005), as even focal brain activity results inwidespread EEG voltage patterns being generated. Thus, relating asurface signal to a specific brain region remains problematic due tothese well-known volume conduction effects (Hoechstetter et al.,2004). When combined with the fMRI evidence, the above conclusionsbecome more valid; however, Egner and colleagues (2005) reportedthese patterns of activation typical of deficient performance on theStroop task in the absence of any behavioral manifestations of thisfunctional dissociation. As no differences in performance betweenhigh and low hypnotic susceptibility groups in and out of hypnosiswere identified, and with recordings from a single electrode pair usedin support of this process, further exploration of these coherence findingsappears warranted.

Spectral Power and HypnosisIn a separate line of inquiry within the hypnosis literature, research

has also sought to explore whether differences in spectral power existto distinguish an alert state from a hypnotic state and whether highand low hypnotizable individuals can be discriminated by spectralpower differences. Research in this area has been popular since the1960s, but early research was restricted by technological and method-ological limitations and as such returned largely equivocal findings(for reviews, see Dumas, 1977; Perlini & Spanos, 1991).

Research in this area has returned few consistent findings but hasfocused largely on the theta and alpha frequency bands (for reviews,

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see Crawford, 1994; Graffin, Ray, & Lundy, 1995). Among the morerecent findings, high hypnotizables have been shown to exhibit greaterabsolute theta power at baseline in frontal and posterior regions thanthose of low hypnotic susceptibility (Graffin et al.; Sabourin, Cutcomb,Crawford, & Pribram, 1990). Further studies have reported greater rel-ative theta power at a central electrode site (Montgomery, Dwyer, &Kelly, 2000) and greater relative low theta power (4–6 Hz) in high hyp-notizables at baseline (Sebastiani, Simoni, Gemignani, Ghelarducci, &Sanatarcangelo, 2003). This correlation between baseline theta andhypnotizability has been described as a robust finding in the literature,proposed to result from attentional differences between high and lowsusceptibility groups (Crawford; Graffin et al.).

While baseline differences in spectral characteristics of high and lowsusceptibility groups have been identified relatively consistently in theliterature, research has yet to identify any consistent change in spectralpower after a hypnotic induction that discriminates high and low hyp-notic susceptibility groups. For example, Graffin et al. (1995) found anincrease in theta and alpha power after hypnosis but no differencesbetween high and low hypnotizability groups. Williams and Gruzelier(2001) explored both questions of baseline differences between high andlow susceptibility groups and distinguishing alert from hypnotic states inhigh and low susceptibility groups. This study examined spectral powerchanges in anterior and posterior electrode sites in baseline, hypnosis,and posthypnosis conditions. Unlike previous research, no differenceswere identified between low and high susceptibility groups at baseline inthe theta frequency band. However, alpha power was found to differenti-ate high and low susceptibility groups at both baseline and hypnosis. Inresting recordings, anterior alpha power was greater in the high suscepti-bility group than in the low group. While during hypnosis the high hyp-notizability group showed an increase in alpha power in posteriorelectrode sites, the low susceptibility group showed a reduction in alphapower from baseline to hypnosis. Theta power was found to increasefrom baseline to hypnosis in both high and low susceptibility groups.

Williams and Gruzelier (2001) reported these findings as identifyingalpha power as an index of the hypnotic experience, because it can beused to discriminate the hypnotic experience between high and lowhypnotizables. These researchers challenged the notion of baselinetheta being an index of hypnotic susceptibility, arguing instead thattheta, particularly in the low range, was more likely an index of relax-ation. This was based on results that low theta was found to increase inhypnosis in both susceptibility groups with no baseline differences. Arecent study also found an increase in theta power for all groups afterhypnotic induction over a variety of hypnotic suggestions; however,the high susceptibility group reported significantly higher theta powerat baseline (Stevens et al., 2004). Given the research with which the

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baseline theta power findings of Williams and Gruzelier are in conflictwith and the novel findings of a frequency-band index of the hypnoticexperience, further exploration is warranted.

Aims and HypothesesWith these recent findings in mind, the present study aimed to fur-

ther address and to explore EEG coherence and power spectralchanges from baseline to hypnosis in individuals of varying levels ofhypnotic susceptibility. To further improve the experimental designfor continuous and consistent EEG recording for all participants, thepresent study used virtual reality hypnosis (VRH) to provide a stan-dardized, controlled hypnotic induction with visual stimuli and audi-tory soundtrack of the hypnotist’s voice. As Egner et al. (2005)identified a functional dissociation between medial and lateral frontalregions in hypnosis, it was predicted that this dissociation will mani-fest itself in state coherence alterations in the form of reduced coher-ence in high hypnotizability groups between medial and lateralelectrode placements in upper alpha and beta (13–30 Hz) frequencybands. In line with the findings of Williams and Gruzelier (2001), base-line theta power (4–8 Hz) was not hypothesized to significantly differbetween high and low susceptibility groups and was predicted toincrease after hypnotic induction for both groups. Should alpha power(8–13 Hz) indeed index the hypnotic experience, it was predicted thatthe high susceptibility group would show greater anterior alphapower at baseline, and an increase in posterior alpha power from base-line to hypnosis, and the low hypnotizability group would show areduction in posterior alpha power from baseline to hypnosis.

METHOD

Participants and Hypnotic SusceptibilitySeventeen right-handed participants (mean age = 21.35, SD = 1.58),

9 females and 8 males, gave informed consent to take part in the study,which had ethical approval from the Swinburne University EthicsCommittee. Participants were assigned to hypnotic susceptibilitygroups based on their responses to the Stanford Hypnotic Clinical Scale(SHCS; Morgan & Hilgard, 1978–1979). The SHCS is a standardizedmeasure of hypnotic susceptibility that involves a spoken hypnoticinduction followed by five hypnotic suggestions; each of which isscored either one or zero. Thus, scores range from zero to five. TheSHCS correlates strongly with other established measures of hypnoticsusceptibility, for example, r = .72 with the Stanford Hypnotic Suscep-tibility Scale; Form C (Bryant, Guthrie, Moulds, Nixon, & Felmingham,2003). The 10 participants that scored between 0 and 2 (M = 1.10,SD = 0.88) were assigned as the low susceptibility group, while the 7

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participants that scored between 3 and 5 (M = 3.57, SD = 0.79) weredesignated as the high susceptibility group.

Hypnotic InductionThe present study provided a controlled hypnotic induction in the

form of a VRH technique. Our study was the first identified study touse VRH technology to explore the neurophysiological processesunderlying hypnosis. Patterson, Tininenko, Schmidt, and Sharar (2004)and Patterson, Wiechman, Jensen, and Sharar (2006) have published aseries of clinical case studies that report the use of VRH to providehypnotic analgesia in a group of burn-injury patients. This workreported reduced pain and anxiety ratings and a concurrent halving inopioid medication (Patterson et al., 2006).

The VRH technique adopted in the present study used a spokenhypnotic induction with suggestions to relax, presented with ambientbackground sounds and scenes of predominantly rivers and bushland(from Virtual Medicine, Aus.). The relaxed hypnotic induction lastedthe first 16 minutes of the program, then hypnotic suggestion wasaimed at maintaining the achieved state until the final moments wherecessation of hypnosis was instructed. Patterson and colleagues (2004,2006) have suggested that the use of VRH may be particularly effectivein achieving successful hypnotic inductions in those not at the extremehigh end of hypnotic susceptibility, because VRH induction is thoughtto be less effortful as the visual stimuli can capture and guide atten-tion. To explore whether VRH may be more effective for the midrangeof susceptibility, the present study used a median split of participantsselected from a normative sample rather than prescreening for extremehigh and low ends of hypnotic susceptibility as is done in much of theliterature (e.g., Graffin et al., 1995).

ProcedureParticipants were seated in an armchair in a darkened room with

legs resting on a footrest the same height as the chair. Following this,participants were fitted with the EEG equipment; the VR equipment,consisting of virtual reality goggles; and shielded earphones. An inflat-able neck pillow was also used to provide support to the neck. Record-ings began with a 2-minute baseline period in which the participantswere instructed to sit still with eyes closed. Following the baselineperiod, the hypnosis stimuli began by running the hypnosis DVD. Thehypnotic induction used the VR equipment to present a 22-minutehypnotic induction with relaxed hypnotic suggestion.

EEG RecordingsEEG recordings were taken from a 32-channel electrode cap (Neuro-

medical Supplies), with electrodes placed according to the international

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10–20 system (Jasper, 1958). Signal was acquired using a Neuroscansystem (Scan, version 3.0, and Synamps amplifiers), which was digi-tized at a rate of 1000 Hz. The amplification was set at 500k, with aband pass filter range of 0.05 Hz and 40 Hz. Recordings were refer-enced to the left mastoid, with the nose as ground. While the mastoidis not entirely electrically neutral (Hagemann, Naumann, & Thayer,2003), it is a commonly used site with low impedance that has beenfound to provide strong spectral power values (Yao et al., 2005). Allimpedances were kept at or below 8kΩ.

Data AnalysisRecordings were analyzed offline (Scan, version 4.30), with a low-

pass filter set at 30 Hz (low-pass slope 48 dB/octave) to remove furtherinterference from the VRH equipment. A window of EEG activity wasselected at baseline and after hypnotic induction. As the present studywas interested in state changes in electrical brain activity, 20-secondwindows of artifact-free EEG were selected 1 minute into the eyes-closed baseline condition, and then 16 minutes 30 seconds into theVRH program. The hypnosis time point was selected, because it was atime where eyes were closed and was approximately 30 seconds afterthe last stage of the spoken induction; the remainder of the programwas aimed at maintaining the achieved state. The recordings werevisually inspected for artifact, and where the desired time windowwas identified as having artifact, the first 20 seconds of artifact-freeEEG that followed was then selected. This never extended beyond30 seconds after the desired time point. Graffin et al. (1995) warn thatcaution should be taken in interpreting many EEG studies of hypnosis,because they compare conditions of eyes open to those of eyes closed.For this reason, the present study used a measure of eyes closed forboth baseline and hypnosis conditions.

Each 20-second window was analyzed in 1-second epochs and base-line corrected. In order to test the coherence hypotheses, averagecoherence values were then calculated for all 21 bipolar combinationsof left frontal electrodes (Fz, F3, Fp1, F7, Fcz, Fc3, Ft7) in upper alphaand beta frequency bands. These frequency bands were selectedbecause decreased coherence in these bands has been shown to reflecta specific functional decrease in coupling between areas (Knyazeva &Innocenti, 2001). One-second epochs were extracted from each 20-second recording using a cosine window with 10% overlap, on which aFast Fourier Transform was then applied. A standard power spectrumwas then obtained from the average of all 20 epochs. The 22nd windowfor each condition was comparable to the minimum window length foreach condition in Williams and Gruzelier (2001). The scalp regionsfrom which spectral data were obtained were similar to that of Williamsand Gruzelier, with a frontal average calculated from F3, Fz, and F4.

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However, the present study used P3, Pz, and P4 to calculate the poste-rior averages rather than O1 and O2, due to signal quality. Averagesfor these electrode pairs were obtained in alpha and theta frequencybands.

RESULTS

A series of mixed-design ANOVAs were conducted using SPSS forWindows (version 13.0) to address both the prediction that left frontalcoherence would decrease from baseline to hypnosis in the high sus-ceptibility group and that posterior alpha power would increase frombaseline to hypnosis for those of high hypnotic susceptibility. Bothcoherence and power spectra values were found to be skewed and assuch were log transformed. Means and standard deviations reportedare prior to log transformation. For the coherence hypotheses, 2 (hyp-notizability) × 2 (condition-baseline/hypnosis) × 21 (electrode pairs)ANOVAs were conducted for beta and upper alpha frequency bandswith pair-wise comparisons in order to establish those electrode pairssuitable for further analysis. The assumption of sphericity was alsoviolated, as such results reported were lower bound corrected for themost conservative adjustment. Spectral analysis was conducted with 4participants removed (3 low susceptibility, 1 high), due to poor signalquality in posterior electrodes. Thus, for the spectral analysis, 6 partici-pants remained in the high hypnotizability group, with 7 in the lowgroup.

CoherenceThe ANOVA for coherence in the upper alpha frequency band

revealed no main effect for condition, F(1, 15) = .12, p > .70; no condi-tion by hypnotizability interaction, F(1, 15) = .99, p > .30; and no three-way interaction between condition, hypnotizability, and electrodes,F(1, 15) = 1.977, p > .10, observed power = .26. Pair-wise comparisonsrevealed no significant differences in upper alpha coherence frombaseline to hypnosis in any of the 21 electrode pairs for low and highhypnotizability groups; thus, no further analysis was conducted forupper alpha coherence.

The ANOVA for coherence in the beta frequency band also revealedno main effect of condition, F(1, 15) = .54, p > .4; no condition by hyp-notizability interaction, F(1, 15) = 3.83, p > .06; and no three-way inter-action between condition, hypnotizability, and electrodes, F(1, 15) = .49,p > .4, observed power = .10. However, a distinct trend could be seen inmean coherence scores for high and low susceptibility groups frombaseline to hypnosis that was in line with predictions (Table 1), wherehigh hypnotizables showed a decrease or no change in coherence in allbut two electrode pairs from baseline to hypnosis, and low hypnotizables

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showed an increase between all electrode combinations. Analysis ofthe pair-wise comparisons for each electrode pair showed that highand low susceptibility groups did not differ significantly at baselineapart from one electrode pair, where the high group showed greaterbeta frequency band coherence at baseline (Fz-Fcz). These comparisonsalso revealed a significant (p < .05) coherence decrease from baseline tohypnosis in high hypnotizables between F3-Fc3, while low suscepti-bles showed a significant increase between Fcz-Fp1, Fz-Fp1, Ft7-F7,and Fc3-F7. The alpha level for these comparisons remained at .05, as it

Table 1Mean Beta Band Coherence Scores for High and Low Hypnotizability Groups at Baselineand Hypnosis for Each Electrode Pair

Electrode Pairs High Hypnotizables Low Hypnotizables

n = 7 n = 10

Baseline Hypnosis Baseline Hypnosis

M (SD) M (SD) M (SD) M (SD)

Fcz-Fz .93 (.04) .91 (.04) .83 (.08) .86 (.10)Fcz-Ft7 .44 (.17) .42 (.14) .35 (.16) .47 (.24)Fcz-Fc3 .80 (.09) .75 (.12) .76 (.12) .80 (.14)Fcz-F3 .77 (.09) * .72 (.07) * .66 (.19) * .71 (.19) *Fcz-F7 .47 (.13) .43 (.14) .40 (.18) .49 (.23)Fcz-Fp1 .69 (.13) .64 (.12) .53 (.22) ** .59 (.24) **Fz-Ft7 .45 (.16) .44 (.15) .35 (.16) .46 (.25)Fz-Fc3 .78 (.09) .73 (.12) .72 (.14) .74 (.18)Fz-F3 .86 (.06) .82 (.07) .77 (.19) .80 (.18)Fz-F7 .51 (.14) .46 (.17) .46 (.20) .52 (.23)Fz-Fp1 .81 (.10) .78 (.10) .66 (.24) ** .70 (.24) **Ft7-Fc3 .48 (.21) .59 (.18) .52 (.17) .62 (.22)Ft7-F3 .57 (.19) .58 (.19) .50 (.19) .59 (.27)Ft7-F7 .85 (.17) .90 (.08) .66 (.24) ** .75 (.26) **Ft7-Fp1 .52 (.16) .52 (.16) .43 (.17) .53 (.28)Fc3-F3 .87 (.05) ** .79 (.10) ** .79 (.14) .83 (.13)Fc3-F7 .60 (.15) .57 (.18) .53(.19) ** .63 (.19) **Fc3-Fp1 .69 (.12) * .60 (.11) * .55 (.27) * .62 (.22) *F7-F3 .64 (.16) .61 (.21) .65 (.20) .74 (.15)Fp1-F3 .86 (.11) .81 (.13) .74 (.26) .81 (.16)Fp1-F7 .62 (.15) .59 (.22) .61 (.23) .68 (.18)

Note. Statistical comparisons are made between baseline and hypnosis for both suscepti-bility groups.

* = Approaching significance (p < .10).** = Significant (p < .05).

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was the intention of these comparisons to identify the electrode pairsin which state changes in coherence had taken place after hypnosis,allowing further analysis. At this significance level, 42 comparisonsshould theoretically result in approximately two false positives in thedata. Given the overwhelming trend and the identification of five sig-nificant changes, it is reasonable to conclude that differences have beenidentified that were not obtained by chance. As the present study wasconcerned with changes in coherence during hypnosis associated withlevels of hypnotizability, two further electrode pairs were identified inwhich the change from baseline to hypnosis for both high and low sus-ceptibility groups were approaching significance (p < .10); these pairswere F3-Fcz and Fc3-Fp1.

Each of the five electrode pairs in which a significant changeoccurred, and the further two approaching significance, were subjectto an individual 2 (hypnotizability) × 2 (condition) mixed-designANOVA to explore the interaction between hypnotizability and coher-ence after hypnotic induction. The alpha level was adjusted to p < .01to control for the number of analyses. Results of these analyses areshown in Table 2.

A significant interaction can be seen between Fcz-Fp1, while interac-tions approaching significance can be seen between Fz-Fp1, Fcz-F3,Fc3-Fp1, F3-Fc3, and Fc3-F7. While no significant interaction wasfound for F7-Ft7, F(1, 15) = .57, p = .461; a main effect of conditionapproaching significance was found, F(1, 15) = 7.83, p = .014, η2 = .34,where coherence was found to increase for both hypnotizabilitygroups between these electrodes from baseline to hypnosis. For each ofthe above interactions, the same trend was evident with an increase incoherence from baseline to hypnosis for the low hypnotizability group,and a decrease in coherence for the high hypnotizability group in thebeta frequency band (see Figure 1). Strong effect sizes were found foreach of the interactions using Hedges’s g, which gives a conservative

Table 2Interaction Results of 2 (condition) by 2 (hypnotizability)ANOVAs

F p Hedges’s g

Fcz-Fp1 9.17 .008 1.42Fz-Fp1 7.50 .015 1.28Fcz-F3 6.58 .022 1.20Fc3-Fp1 6.55 .022 1.20F3-Fc3 7.80 .014 1.31Fc3-F7 4.20 .058 0.96

Note. df = 1, 15.

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(a) Low susceptibility group

0.3

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Fcz-Fp1 Fcz-F3 F3-Fc3 Fc3-Fp1 Fz-Fp1 Fc3-F7 F7-Ft7Electrode pair

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Hypnosis

Figure 1. Mean beta coherence values at baseline and hypnosis in the low hypnotizabilitygroup (a) and high hypnotizability group (b).

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Fcz-Fp1 Fcz-F3 F3-Fc3 Fc3-Fp1 Fz-Fp1 Fc3-F7 F7-Ft7Electrode pair

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Hypnosis

(b) High susceptibility group

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106 DAVID WHITE ET AL.

estimate in small sample sizes, providing further evidence of thisdecrease in coherence for the high hypnotizability group with theopposite for the low hypnotizability group (see Figure 2).

Spectral PowerAs in Williams and Gruzelier (2001), a 2 (condition) × 2 (region) × 2

(hypnotizability) ANOVA was conducted for both alpha and thetabands. Unlike the previous study, the present study did not use nar-row band analysis to differentiate high and low alpha and theta as thefindings of the previous study in the alpha band were largely general-ized to the entire frequency band. Mean absolute power in anteriorand posterior electrode placements for theta and alpha frequencybands are provided in Table 3 for high and low susceptibility groups.

For the theta frequency band, no significant main effect for condition,F(1, 11) = .93, p > .35, or region, F(1, 11) = .33, p > .5, and no significantinteraction was observed between condition, region, and susceptibility,F(1, 11) = 1.04, p > .3, observed power = .15. No further main effects orinteractions were significant, with pair-wise comparisons showing nosignificant differences between high and low susceptibility groups for

Figure 2. Sites of beta coherence changes from baseline to hypnosis.

O2O1Oz

PzP4

CP4

P8

C4

TP8

T8

P7 P3

CP3 CPz

Cz

FC4FT8

TP7

FCz

F4F8

T7

FT7FC3

F3

FP2

F7

FP1

C3

Fz

= Increase Approaching Sig. = Significant Interaction = Interaction Approaching Sig.

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EEG CORRELATES OF VIRTUAL REALITY HYPNOSIS 107

baseline and hypnosis. As such, no further analysis was conducted inthe theta frequency band.

In the alpha frequency band, no significant main effect for condi-tion, F(1, 11) = .93, p > .35, and no significant interaction was observedbetween condition, region, and susceptibility, F(1, 11) = 2.48, p > .1,observed power = .30. As could be expected, a significant main effect wasfound for region, with post hoc t tests showing alpha was significantlyhigher in posterior regions than anterior regions, t(13) = 4.74, p < .001.Unlike Williams and Gruzelier (2001), no significant differences inanterior alpha power were observed at baseline, t(11) = .12, p > .90. Inorder to conduct a more direct comparison with Williams’s and Gruze-lier’s results, a 2 (condition) x 2 (hypnotizability) ANOVA was con-ducted on posterior alpha, where the previous study identified thedifferential alpha power changes according to hypnotic susceptibility.Results of this analysis showed an insignificant interaction betweencondition and hypnotizability, F(1, 11) = 2.80, p > .10, observedpower = .33; however, analysis of this interaction showed an insignifi-cant trend in line with the previous research (see Figure 3).

DISCUSSION

The trends reported in the present study are consistent with electro-physiological findings reported in the literature. The results of coher-ence analysis further implicate a role for frontal processes in hypnosis,while the spectral analysis identified a trend in line with the work ofWilliams and Gruzelier (2001). Coherence in the upper alpha banddid not provide any evidence of the hypothesized frontal inhibition ordissociation. However, a clear trend was noted in the beta frequency

Table 3Mean Absolute Power Values in Theta and Alpha Frequency Bands for High and LowSusceptibility Groups

High Hypnotizables Low Hypnotizables

n = 6 n = 7

Baseline Hypnosis Baseline Hypnosis

M (SD) M (SD) M (SD) M (SD)

ThetaAnterior 9.93 (6.57) 23.19 (26.80) 10.95 (8.96) 10.88 (8.06)Posterior 12.17 (12.60) 12.16 (10.70) 13.09 (9.00) 10.73 (6.62)

AlphaAnterior 15.90 (17.66) 16.74 (18.98) 14.96 (8.97) 12.86 (10.51)Posterior 21.63 (11.15) 37.76 (27.69) 44.02 (30.24) 31.26 (19.52)

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108 DAVID WHITE ET AL.

band in which coherence between medial frontal and lateral frontalelectrode placements decreased for those in the high susceptibilitygroup while increasing in the low susceptibility group. In the spectralanalysis, no differences were identified at baseline in either alpha ortheta frequency bands, further contradicting earlier work that identi-fied baseline differences in theta power between low and high suscep-tibility groups but also failing to replicate the work of Williams andGruzelier in resting alpha power. Evidence of theta power as an indexof relaxation could not be found, because no increase in theta powerwas observed from baseline to hypnosis in either susceptibility group.Finally, no significant differences were found in posterior alpha powerduring hypnosis. However, the identified trend was in line with thefindings of Williams and Gruzelier.

Coherence FindingsCoherence analysis produced results similar to the previous research,

identifying a decrease in connectivity within left frontal regions. Unlikethe unpublished experiment by Kaiser (cited in Gruzelier, 1998, 1999),the present study identified no significant changes in upper alpha coher-ence as a result of hypnosis. However, the present study extended thecoherence analysis to the beta frequency band, also shown to decrease

Figure 3. Mean posterior alpha power for high and low susceptibility groups at baselineand hypnosis.

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EEG CORRELATES OF VIRTUAL REALITY HYPNOSIS 109

where functional coupling is decreased (Knyazeva & Innocenti, 2001),and found a similar trend. An interaction between susceptibility wassignificant in one electrode pair and approaching significance for severalfurther pairs. In the high susceptibility group, beta coherence decreasedfrom baseline to hypnosis between frontal electrode placements largelyin the medial and lateral prefrontal regions. This pattern was reversed inthe low susceptibility group, where an increase in coherence wasobserved. As most of these interactions did not reach statistical signifi-cance, they must be interpreted with caution, especially given the impre-cise nature of the coherence technique (Hoechstetter et al., 2004).However, the trend is evident in a number of electrode pairs con-fined to a localized region with strong effect sizes, thus implicating afunctional dissociation within this region. This interaction was notedlargely between electrode pairs located on and near the mid-lineand more lateral prefrontal regions (Fcz-Fp1, Fz-Fp1, Fcz-F3, Fc3-Fp1, F3-Fc3, and Fc3-F7). Interestingly, both high and low suscepti-bility groups showed an increase in beta coherence between onelateral electrode pair approaching significance (F7-Ft7). This suggeststhat the proposed dissociation is not generalized to the entire leftfrontal region but is restricted to connectivity between medialregions and medial to lateral regions, further supporting the workof Egner et al. (2005), Fingelkurts et al., (2007), and Kaiser (cited inGruzelier, 1998, 1999).

As these studies have all identified a decrease in frontal coherencein high susceptibility groups during hypnosis, the evidence implicatinga functional dissociation or inhibition of frontal regions in hypnosis isgrowing. Both the neurophysiological (Crawford, 1994; Gruzelier,1998) and dissociated control (Bowers, 1992) models of hypnosis findsupport in these results. With respect to the dissociated control modelof hypnosis, communication between the executive control and thesubordinate, more automated, systems of control may become com-promised (Woody & Sadler, 1998). This dissociation was evident usingfMRI during completion of the Stroop task and has now been demon-strated in both event-related EEG coherence (Egner et al. 2005) and as astate change as a result of hypnotic induction in the present study.Similarly, the neurophysiological model of hypnosis (Crawford;Gruzelier, 1998) argues that the “letting go” component of hypnoticinduction is characterized by an inhibition of frontal attentional sys-tems. These results also support the view of Dietrich (2003), who hasproposed a model whereby frontal inhibition forms the basis of allaltered states of consciousness.

The present study was able to provide further evidence of statechanges in left frontal functioning, particularly reinforcing the hypothesisof a functional dissociation between medial and lateral prefrontal areasin hypnosis for those of high hypnotic susceptibility (Egner et al.,

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110 DAVID WHITE ET AL.

2005). Medial frontal regions, in particular anterior cingulate cortex(ACC), have been implicated in hypnotic processes using several othertechniques. Croft, Williams, Haenschel, and Gruzelier (2002) reportedthat although subjective ratings of pain in response to electrical stimu-lation were initially predicted by gamma activity over prefrontalregions, this relationship was no longer present in high hypnotizablesafter hypnotic induction. The source of this gamma relationship wasattributed to the ACC region using low resolution electromagnetictomography (LORETA), suggesting that ACC function is compro-mised in hypnosis for those high in hypnotic susceptibility. In aseparate study of hypnotic analgesia, EEG coherence between soma-tosensory regions and frontal sites, including ACC, were found todecrease during successful hypnotic analgesia (Miltner, Trippe,Friederich, Ozcan, & Weiss 1999). Positron emission tomography(PET) studies have suggested that activity in ACC also mediates thesuccessful experience of hypnotic analgesia (Faymonville et al., 2000;Rainville et al., 1999) and that subjective reports of relaxation andabsorption in hypnosis are correlated with ACC activity (Rainville,Hofbauer, Bushnell, Duncan, & Price, 2002). These findings furthersupport neurophysiological and dissociated control models of hypno-sis, as ACC has been proposed as an important part of the executiveattentional network (Fan, McCandliss, Fossella, Flombaum, & Posner,2005). The evidence is mounting in support of altered functioning ofACC in hypnosis, particularly through dissociation in communicationwith other areas. The present study and the work of Egner et al. founddissociation between medial and more lateral frontal areas, whileothers have identified a decrease in coherence between frontalattentional areas and somatosensory sites during hypnotic analgesia(Miltner et al.). As such, compromised function or communicationfrom frontal executive attentional sites and other cortical regionsappears to be a common mechanism underlying several aspects of thehypnotic experience.

Frequency Band FindingsAs in the previous EEG power analysis study (Williams & Gruzelier,

2001), theta power was not found to differ at baseline between the highand low susceptibility groups; however, it was not shown to increaseas a function of relaxed hypnotic induction. One important differencebetween the present study and the work of Williams and Gruzelier isthe analysis of high and low alpha and theta power. In the work ofWilliams and Gruzelier, the trends seen in the alpha band were gener-alized largely to the entire band, while the indexing of relaxation wasconfined largely to the low theta band (3.5–5.5 Hz). This may explainthe failure of the present study to identify changes in theta as a functionof relaxation. An explanation for the lack of differences at baseline may

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lie in the characteristics of the sample adopted in the present study.While the majority of studies in which baseline differences have beenobserved used those at the extreme ends of hypnotic susceptibility,the present study used a normative sample. Williams and Gruzelieridentified no significant differences at baseline between high and lowsusceptibility groups when using the 67th and 33rd percentiles todetermine susceptibility groups; however, when Graffin et al. (1995)adopted a more stringent criteria of 90th and 20th percentiles,baseline differences were noted. Thus, differences in spectral powerat baseline may only be apparent in more extreme susceptibilitysamples.

Finally, limited support was found for posterior alpha power index-ing the hypnotic experience for highs and lows in the form of a nonsig-nificant trend. In line with the previous study, posterior alpha powerwas found to increase in hypnosis for the high susceptibility group,while the low susceptibility group showed a decrease from baseline tohypnosis. As the present study was forced to omit the results of 4 par-ticipants from spectral data analysis due to signal quality, it may bethat the analysis lacked the statistical power to identify any significantfindings. Given the use of a normative sample, it may be that the iden-tification of a nonsignificant trend in line with Williams and Gruzelieris a result of a less dramatic change in hypnosis with insufficientnumbers to detect such an interaction.

Spectral analysis of high and low susceptibility groups at baselineand hypnosis demands further exploration. The present study foundsupport for the idea that no significant differences would be foundbetween high and low susceptibility groups in the theta frequencyband at baseline resting conditions; however, it was suggested that thismay be a product of sample selection criteria. Future research couldexplore the baseline spectral power characteristics of low, medium,and high hypnotic susceptibility groups to further investigate the pos-tulations of Williams and Gruzelier. Resting recordings have moder-ately high test-retest reliability (McEvoy & Smith, 2000). But beingrelatively unable to control for individual cognitive processes at thistime may be an underlying source of these variable findings. Futureresearch could utilize a simple task in an attempt to control for thisvariability to further identify any baseline differences in spectralpower. Narrow band analysis could be utilized to further explore therole of the low theta frequency band in hypnosis and relaxation. Theproposed frequency band index of the hypnotic experience in the formof posterior alpha power remains an exciting prospect after years ofequivocal findings. The trend identified in the present study is in linewith the work of Williams and Gruzelier (2001), but further work in alarger sample could provide further insight into this hypothesizedindex of hypnosis.

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Williams and Gruzelier (2001) suggest that a greater ability to “letgo” in hypnosis is the basis of the increased posterior alpha power.Should future research further support an increase in posterior alphapower as an index of hypnotic experience, then an expansion of thisexplanation is necessary. Pfurtscheller, Stancak, and Neuper (1996)reviewed literature in support of the “idling hypothesis,” which sug-gests that enhanced rhythms within the alpha band are characteristicof an area of cortex that has passed into an “idling” state of reducedcognitive work. Functional imaging studies have identified a negativecorrelation between blood flow and metabolism and alpha activity inposterior regions (Danos, Guich, Abel, & Buchsbaum, 2001; Laufs et al.,2003; Sadato et al., 1998). Should this posterior alpha power index ofhypnotic susceptibility be replicated with future research, it may bethat greater regions of cortex become idle in a deep state of hypnosis.

VRHWhile the spoken hypnotic induction is comparable to a standard

induction, any effect of the VR technology remains unknown. In beingable to obtain results in a normative sample that are comparable tothose previously reported in studies utilizing the more extreme ends ofhypnotic susceptibility, the present study may have also provided evi-dence of the efficacy of the use of VR technology in hypnosis. It hasbeen previously suggested that VRH may be more effective in achiev-ing successful hypnotic inductions in those not at the extreme high endof hypnotic susceptibility, as the visual stimuli can make the inductionprocess less effortful (Patterson et al., 2004, 2006), with the presentstudy supporting this claim. Patterson and colleagues reported theefficacy of VRH in pain reduction in burn patients, and results of thepresent study suggest that this technology is accessible and effectivefor those not on the extreme high end of hypnotic susceptibility. Cer-tainly, the work of Patterson and colleagues taken with the presentfindings would suggest VRH technology warrants further explorationas a tool both in providing a controlled hypnotic induction in hypnosisresearch and in effectively treating a wider clinical population for painmanagement and other medical and psychological settings.

CONCLUSIONS

The present study was able to further implicate frontal attentionalprocesses in the hypnotic process. The ACC was highlighted as beingof particular importance in the hypnotic experience for its role in exec-utive attention, and in light of recent findings in relaxed hypnosis andhypnotic analgesia. Limited support was also found for posterior alphapower indexing the hypnotic experience, and the idling hypothesis wasproposed as an explanatory mechanism. Should future research replicate

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EEG CORRELATES OF VIRTUAL REALITY HYPNOSIS 113

posterior alpha power increasing in hypnosis for those high in hypnoticsusceptibility, a greater abundance of idle brain regions may form theunderlying basis of such a finding. Finally, VRH was proposed as atechnique ideal for providing effective hypnotic induction in those noton the extreme high end of hypnotic susceptibility, making it an excit-ing prospect in providing a controlled hypnotic induction for futureresearch and in medical settings.

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EEG Korrelate von Virtuelle-Realitäts-Hypnose

David White, Joseph Ciorciari, Colin Carbis und David LileyZusammenfassung: Diese Studie untersuchte hypnosebezogeneVeränderungen der elektroenzephalographischen (EEG) Kohärenz undLeistungsspektra an einer Stichprobe von gering und hochhypnotisierbaren Teilnehmern (Stanford Skala). Hypnose wurde mittelseines VR-Hypnose Induktionssystems eingeleitet. In dieser Studie wurdedas EEG von 17 Teilnehmern (Mittleres Alter 21.35, Standardabweichung1.58) unter Einbeziehung ihrer Hypnotisierbarkeitswerte verglichen. DieEEG-Aufzeichungen aus einer 2 Minuten andauernden Ruhephase (Augengeschlossen) wurden mit einem hypnotisierten Zustand verglichen. Diesesneue Induktionssystem konnte EEG Befunde aus der Literatur replizieren.Signifikante Interaktionen wurden für die Beta-Kohärenz beobachtet. DieGruppe hochsuggestibler Teilnehmer (n = 7) wies eine Reduktion derKohärenz auf, wohingegen die Geringsuggestiblen (n = 10) mit einemAnstieg zwischen medial frontalen und linken lateral-präfrontalenSensoren reagierten. Methodologische und effizienzbezogene Themenwerden besprochen.

RALF SCHMAELZLE

University of Konstanz, Konstanz, Germany

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116 DAVID WHITE ET AL.

Corrélation entre l’EEG et l’hypnose en réalité virtuelle

David White, Joseph Ciorciari, Colin Carbis et David LileyRésumé: L’objet de cette recherche concernait les changements dans lacohérence électroencéphalographique (EEG) liée à l’hypnose et dans lesspectres de puissance chez des sujets hautement hypnotisables oufaiblement hypnotisables (selon l’échelle clinique d’hypnotisabilité deStanford), hypnotisés par un système d’induction d’hypnose en réalitévirtuelle. Dans le cadre de cette étude, les électroencéphalogrammes de 17sujets (âge moyen = 21,35 ans, écart type = 1,58) ont été comparés en fonctiondu niveau d’hypnotisabilité des sujets. Les résultats de l’EEG associés à unétat de référence d’une durée de deux minutes, les yeux clos, ont étécomparés avec les EEG effectués durant un état lié à l’hypnose. Ce systèmed’induction novateur a produit des résultats EEG correspondant à ceux depublications précédentes sur l’hypnose. Des interactions significatives ontété relevées avec la cohérence électroencéphalographique bêta. Le groupehautement hypnotisable (n = 7) a montré une cohérence décroissante, alorsque le groupe faiblement hypnotisable (n = 10) a montré une augmentationde la cohérence entre les sites frontal médian et préfrontal latéral gauche.Des enjeux liés à la méthodologie et à l’efficacité font l’objet d’un examen.

JOHANNE REYNAULT

C. Tr. (STIBC)

Correlatos EEG de la hipnosis de realidad virtual

David White, Joseph Ciorciari, Colin Carbis, y David LileyResumen: El estudio investigó cambios electroencefalogáficos (EEG) encoherencia y poder de frecuencia relacionados a la hipnosis en personas conalta y baja hipnotizabilidad (medida según la Stanford Hypnotic ClinicalScale) inducidos por un sistema de inducción hipnótica virtual de realidad(VRH). En este estudio, comparamos el EEG de 17 participantes (edad media =21.35, DE = 1.58) en base a su grado de hipnotizabilidad. Comparamos elregistro EEG asociado a una línea base de 2-minutos con los ojos cerradoscon el EEG asociado a la hipnosis. Este sistema novedoso de inducción fuecapaz de producir cambios EEG consistentes con la literatura previa dehipnosis. Encontramos interacciones significativas en EEG en la coherenciade beta. El grupo con alta susceptibilidad (n = 7) mostró una coherenciadisminuida, mientras que el grupo de baja susceptibilidad (n = 10) mostróun aumento en la coherencia entre las areas prefontales media frontal ylateral izquierda. Discutimos puntos metodológicos y de eficacia.

ETZEL CARDEÑA

Lund University, Lund, Sweden

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