Consciousness and Cognition 21 (2012) 100–116

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Consciousness and Cognition

journal homepage: www.elsevier .com/locate /concog

Suggested visual hallucination without hypnosis enhances activityin visual areas of the brain

William J. McGeown a, Annalena Venneri b,c,1, Irving Kirsch d, Luca Nocetti e, Kathrine Roberts a,Lisa Foan a, Giuliana Mazzoni a,⇑a Department of Psychology, University of Hull, UKb Department of Neuroscience, University of Sheffield, Sheffield, UKc S. Camillo Research Hospital, IRCCS, Venice, Italyd Harvard Medical School and Beth Israel Deaconess Medical Center, United Statese Azienda Universitaria-Ospedaliera Policlinico, Modena, Italy

a r t i c l e i n f o

Article history:Received 21 February 2011Available online 27 November 2011

Keywords:SuggestibilityHypnosisColorPerceptionBrain imaging

1053-8100/$ - see front matter � 2011 Elsevier Incdoi:10.1016/j.concog.2011.10.015

⇑ Corresponding author. Address: Department ofE-mail address: g.mazzoni@hull.ac.uk (G. Mazzo

1 AV had a collaboration with the Department of Necollection for this study took place.

a b s t r a c t

This functional Magnetic Resonance Imaging (fMRI) study investigated high and low sug-gestible people responding to two visual hallucination suggestions with and without ahypnotic induction. Participants in the study were asked to see color while looking at agrey image, and to see shades of grey while looking at a color image. High suggestibleparticipants reported successful alterations in color perception in both tasks, both in andout of hypnosis, and showed a small benefit if hypnosis was induced. Low suggestible peo-ple could not perform the tasks successfully with or without the hypnotic induction. ThefMRI results supported the self report data, and changes in brain activity were found ina number of visual areas. The results indicate that a hypnotic induction, although havingthe potential to enhance the ability of high suggestible people, is not necessary for theeffective alteration of color perception by suggestion.

� 2011 Elsevier Inc. All rights reserved.

1. Introduction

Hypnosis consists of two components, a hypnotic induction, during which a presumed hypnotic state is induced, followedby a series of suggestions for various changes in experience and behavior (Oakley & Halligan, 2009). Hypnotic inductionstypically contain requests for the participant to relax and enter a hypnotic state. Typical hypnotic suggestions can ask forthe production of automatic movements, temporary paralyses, hallucinations, and alterations in memory or other cognitivefunctions. One of the major unresolved issues in research on hypnosis refers to the relation between these two componentsof hypnosis (Kirsch & Lynn, 1995; Lynn, Kirsch, & Hallquist, 2008; Oakley, 2008; Oakley & Halligan, 2009). Is the induction ofa hypnotic state necessary for the experience of hypnotic suggestions, does it increase the likelihood of responses to sugges-tion, does it enhance the response to a suggestion, or is it merely an epiphenomenon, with no causal relation to theexperience of subsequent suggestions?

We have recently found that in highly suggestible persons, hypnotic induction procedures produced a condition in whichanterior default mode activity was reduced during hypnosis without increasing activity in other cortical regions (McGeown,Mazzoni, Venneri, & Kirsch, 2009). These changes were observed by carrying out an analysis on the brain activity that

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Psychology, University of Hull, Cottingham Road, Hull HU6 7RX, UK. Fax: +44 1482 465599.ni).uroscience at the University of Modena and Reggio Emilia, Italy, funded by a grant from MIUR when data

W.J. McGeown et al. / Consciousness and Cognition 21 (2012) 100–116 101

occurred during numerous rest periods which were found between suggestions to which the participants were instructed torespond. Reductions in default mode activity typically occur when people actively engage in a goal-directed cognitive taskwith an external focus, rather than merely letting their minds wander. The decrease in anterior default mode activity in highsuggestible participants when resting under hypnosis suggests that during the alleged hypnotic state subjects were able tosuspend spontaneous non-goal-directed, internally focused cognitive activity (e.g., daydreaming, self referential processing),in the absence of a task. This change in brain activity reflects an active adjustment in highly suggestible participants duringwhich they may prepare themselves for any suggested future activity that they may be required to perform.

In another previous study, we found that highly suggestible participants reported experiencing suggested visual halluci-nations when no hypnotic state had been induced, and they did so to a similar level as experienced following hypnotic induc-tion (Mazzoni et al., 2009). The data from the study by Mazzoni et al. (2009) suggest that the hypnotic state might be anepiphenomenon, in that it is not required nor does it facilitate the experience of suggestion. As the data reported by Mazzoniand colleagues were based on self-report alone, we used fMRI in the present study to further examine the relation betweenthe induction of a hypnotic state and the experience of suggested visual illusions. Our questions were: does the induction ofhypnosis in highly suggestible subjects enhance the effects of suggestions for perceptual alterations and if so is the increasedability related to alterations in the level of activity in areas of the visual cortex associated with color perception?

The effects of hypnotic induction on neurophysiological activity and on the neurophysiology of suggestion have been theobject of investigation in several studies (reviewed in Oakley & Halligan, 2010). The most pertinent to the study reportedhere was that carried out by Kosslyn and colleagues (2000). The authors used Positron Emission Tomography (PET) tocompare brain activity with hypnotic and non-hypnotic suggestions to alter color perception. Our study was designed asa replication and extension of the Kosslyn et al. study.

Kosslyn et al. (2000) reported that hypnotic suggestions to perceive color in a grey-scale stimulus and to drain color froma colored stimulus altered brain activity bilaterally in the extrastriate visual cortex of highly suggestible subjects. They alsoreported that these changes in activation were limited to the right hemisphere when the participants were asked to imaginechanges in color without the induction of hypnosis. The authors interpreted their results as indicating that suggestion-re-lated perceptual changes require the induction of a hypnotic state. However, this study confounded the induction of hypno-sis with the wording of the suggestions for altered perception. In hypnosis there was a suggestion that they would ‘see’ thecolors as different from what they really were, but in the no-hypnosis condition participants were instead asked to ‘remem-ber and visualize’ the differences in color. Hence, it is not possible to know whether the differences in brain activation weredue to the induction of hypnosis (as the authors suggested) or to the difference in wording used to elicit the reported changesin color perception. Differences in the wording of hypnotic suggestions are crucial, as there is a clear difference in brain acti-vation depending on whether the participant is given a suggestion to experience, or asked to imagine a subjective change(e.g., Derbyshire, Whalley, Stenger, & Oakley, 2004 [pain]; Szechtman, Woody, Bowers, & Nahmias, 1998 [auditoryhallucination]).

In our study the suggestion provided to the participants was kept constant between hypnotic and non-hypnotic condi-tions. This enabled an accurate assessment of the effects of hypnosis per se on color altering ability. The brain areas associ-ated with color perception (veridical viewing) have been reported in a number of research articles. In a study using PET, Zekiet al. (1991) identified an area located across the lingual and fusiform gyri (termed V4) which was uniquely associated withthe perception of color. Activation to color was observed bilaterally, but was greater on the left. Other brain regions were alsoactive for the color stimuli, including the striate cortex (V1) and the adjacent cortical region (V2); however, the activation ofthese brain regions was not specific to color stimuli, in that they also showed changes in activation in response to motionstimuli. Studies using fMRI have also identified a role for the fusiform and lingual gyri in the processing of color (e.g., Beau-champ, Haxby, Jennings, & DeYoe, 1999). Studies of achromatopsia further highlight the association of the lingual andfusiform gyri in color perception (e.g., Bouvier & Engel, 2006). In the current study, the monitoring of changes in brain activ-ity in the fusiform and lingual gyri enabled us to differentiate alterations in brain activity that occurred due to suggestionfrom those resulting from hypnotic induction and suggestion. Rather than focus only on those regions however, in thecurrent study a whole brain fMRI analysis was carried out. This allowed us to identify the neural circuit used to performthe color alteration tasks.

This study differed from the Kosslyn et al. (2000) study in two other ways. First, we had participants report the vividnessof the color they perceived during the tasks using a rating scale, unlike in the study by Kosslyn et al. (2000) in which they hadto only inform the investigators whether they could see color or not. Besides allowing us to compare the effect of hypnoticinduction on self-reported subjective responses, this method also allowed us to analyze correlations between self-reportedexperiences of altered color perception and changes in brain activation. Second, in the current study, the responses of lowsuggestible participants were also assessed. Accepting the conventional presumption that low suggestible participants arenot capable of being hypnotized, we had the opportunity to discriminate induction effects that are specific to hypnosis fromthose that are produced by non-hypnotic aspects of the induction procedure, such as simple relaxation.

To summarize, Kosslyn et al. (2000) did not assess the effect of hypnosis by providing participants with an identically-worded suggestion for visual alterations with and without the hypnotic induction, nor did they assess self-reports of theintensity of the color alterations that occurred in participants. The present fMRI study assessed whether self reports of visualalterations of perception are accompanied by bilateral changes in color-responsive areas of the visual cortex and whether thechanges of experience are associated with alterations in brain activation produced by the induction of hypnosis.

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2. Method

2.1. Participants

Two hundred and sixty-three potential participants were screened for hypnotic suggestibility with a modified version ofthe Carleton University Responsiveness to Suggestion Scale (CURSS) (Comey & Kirsch, 1999; Spanos et al., 1983). Those scor-ing in either the high (5–7) or low (0–1) range of suggestibility were invited for further participation. In a second screeningsession, potential participants were asked individually, both in and out of hypnosis, to respond to suggestions to see a grey-scale stimulus as if it were in full color and to see a colored stimulus as if it were in shades of grey. The CURSS, used in thefirst screening session, consists of a hypnotic induction and seven hypnotic suggestions. Six of the suggestions are scored byparticipants’ ratings indicating whether or not they had responded behaviorally to the suggestion. A score of one is assignedfor each suggestion that the person responds to behaviorally. The seventh suggestion requests temporary amnesia for thefirst six suggestions. A score of one is recorded if there is at least one suggestion that is recalled before the suggestionand after its cancellation, but not in the intervening period. For the second screening session, participants were first informedthat the purpose of the study was to assess their ability to experience colored stimuli as if they were grey and grey stimuli asif they were colored, both in and out of hypnosis. They were then made familiar with the two stimuli (see Fig. 1). On each offour trials, two of which were preceded by a hypnotic induction taken from Kirsch, Lynn, and Rhue (1993), participants wereasked to first see the stimulus as it actually was (in color or in shades of grey). Then, following a pause of 10 s, they wereasked to alter their perception of the stimulus. When shown the grey-scale pattern, the suggestion was to alter their percep-tion by adding color, so that they actually saw it in full color. When shown the colored pattern, the suggestion was to draincolor so that they only saw shades of grey. Most of the highly suggestible participants, but none of the low suggestibleparticipants, reported being able to alter their color suggestion. Eleven highly suggestible participants (CURSS mean = 5.82,SD 0.87) who were able to respond to these color alteration suggestions were included in the fMRI study, along with sevenlow suggestible participants (CURSS mean = 0.29, SD 0.49) who reported that were unable to experience any color alteration.

2.2. Procedure

This study received approval by the local ethics committee at the University of Modena and Reggio Emilia, Modena, Italy,where scanning for this study took place. Participants were informed that the purpose of the study was to assess what hap-pens in the brain when people respond to suggestions for perceptual alterations both in and out of hypnosis. They were toldthat while in the scanner, they would see a screen with a fixation point on which they had to focus their eyes, that thefixation point would be followed by a pattern which they had to look at, and that this would then be followed by a signalto alter their perception of the pattern. They were also told that this would be done in and out of hypnosis. After explainingthe experimental procedure, informed consent was obtained for all participants. Participants were familiarized with thescanning environment and procedures, before the scanning session.

The fMRI task followed a block design. During the time of scanning each participant experienced a rest period (20 s), pas-sive viewing of a greyscale Mondrian-like pattern (30 s), the same greyscale pattern with the suggestion to add color (30 s), aperiod in which they had to rate the intensity of the color that they had seen during the add condition (14 s), another restperiod (20 s), passive viewing of a full color Mondrian-like pattern (30 s), the same color pattern with the suggestion to drainthe color (30 s), and a period in which they had to rate how much color they saw during the drain condition (14 s). Each ofthese conditions was repeated four times in each run and the color and greyscale trials were counterbalanced within andacross runs. There were 4 runs in total (2 which were subsequent to a hypnotic induction, 2 in the absence of a hypnoticinduction). The hypnosis/no hypnosis conditions were counterbalanced across participants with half being imaged underhypnosis first and the other half out of hypnosis first, to ensure that any potential order effects (participant or scannerrelated) would not affect the findings.

Fig. 1. Mondrian-like greyscale and color and patterns used in the fMRI experiment. (For interpretation of the references to color in this figure legend, thereader is referred to the web version of this article.)

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Hypnosis was induced using an abbreviated version of the induction described by Kirsch et al. (1993). Suggestions andtask instructions were kept constant for the hypnosis and no hypnosis runs, thus ensuring that the effects of hypnotic induc-tion on brain activation would not be confounded by these factors. These were composed of perceptual alterations (add colorto the greyscale pattern or drain color from the colored pattern). The Mondrian-like patterns used as stimuli are shown inFig. 1.

During the active tasks of adding and draining color participants rated how much color they perceived during eachcondition with an fMRI compatible response box using a 1–5 point scale, in which 1 indicated no color at all and 5 indicatedfull color.

At the end of the fMRI session participants were also asked to indicate the degree to which they felt hypnotized on acommonly used four point scale (normal state, relaxed, hypnotized, and deeply hypnotized) (Hilgard & Tart, 1966) for boththe hypnosis runs and the no-hypnosis runs. Although the scale might confound relaxation and hypnosis, we used it to facil-itate comparisons with the results of previous studies.

2.3. fMRI methods

Echo planar T2� weighted MRI images were acquired on a 3T Philips Achieva MRI system (TR = 2 s, TE = 35 ms, flipangle = 80�, voxel dimensions 1.88 � 1.88 � 3.00 mm, field of view 240 mm, matrix 128 � 128 � 30). Three hundred andseventy-six volumes of 30 contiguous slices were acquired in each run. Each run was preceded by 30 s of dummy scansto allow the scanner to reach equilibrium. Four runs were obtained, two in hypnosis and two out of hypnosis. During dataacquisition, one of the high suggestible participants had excessive movement and was, therefore, excluded from the analy-ses. This left the high suggestible group with 7 females and 3 males between the ages of 20 and 53 (mean 25.00, SD 10.32).The low suggestible group had 5 females and 2 males between the ages of 20 and 35 (mean 26.86, SD 6.54).

2.4. fMRI data analysis

Imaging data were analyzed using Statistical Parametric Mapping (SPM5) image analysis software (Wellcome Centre forNeuroimaging, London, UK). All volumes from each subject were realigned after creating a mean as reference and re-slicedusing 4th Degree B-Spline interpolation methods to adjust for residual motion related signal changes. Images were spatiallynormalized to the standard EPI template available in SPM5 using non-linear estimation of parameters. Normalized imageswere then spatially smoothed with an 8 mm full width at half maximum isotropic Gaussian kernel to compensate for anyresidual variability after spatial normalization. A boxcar waveform convolved with a synthetic hemodynamic response func-tion (HRF) was used as the reference waveform for each condition. Image data were high-pass filtered with a set of discretecosine basis functions with a cut-off period of 128 s. As described above, head motion was less than 3 mm in all volunteersbut one, whose scans were not included in the analysis. Head motion was included as a regressor in the first level analysesfor the remaining participants.

At first level, all four runs for each participant were entered into an analysis using the general linear model. Contrastswere defined to evaluate changes in brain activity due to color adding (adding color to the greyscale pattern; versus lookingat the greyscale pattern) and color draining (draining color from the colored pattern versus looking at the color pattern), bothin and out of hypnosis. Adding color (Add) refers to the visual hallucination condition, whereas looking at the greyscale pat-tern (Look) refers to veridical perception.

Separate 2 � 2 analyses of variance (ANOVA) with participant (high or low suggestible) and hypnosis (with or without) asthe main factors were carried out on the contrast images produced in the 1st level analysis for each of the tasks (color adding,color draining). This allowed us to investigate whether there were any interactions between participant and hypnosis oneach of the tasks. Paired samples t-tests were used to compare the high suggestible participants when in hypnosis comparedto out of hypnosis. The interaction images from the relevant 2 � 2 ANOVAs were used as an inclusive mask in these analyses.

Random effect analyses were carried out by entering each set of contrast images from the 1st level analyses into one sam-ple t-tests. This enabled the brain areas used in each of the tasks to be identified for the high and low suggestible participantsseparately when in and out of hypnosis.

Correlation analyses were carried out to examine the association between the participants’ self-reports of color percep-tion and the changes in brain activity during the color alteration tasks. The relationship between the level of hypnosis thatparticipants achieved and the changes in brain activity during the color alteration tasks was also examined.

A previous analysis, which focused on the resting state data obtained in these participants (McGeown et al., 2009) showedthat the high suggestible participants had deactivation in anterior default mode areas when hypnotized. Because of this find-ing, a further correlation analysis was carried out for the present article to examine whether greater levels of anterior defaultmode deactivation during hypnosis in rest were related to greater changes in brain activity when performing the color add-ing task when in hypnosis, compared to when out of hypnosis. In other words, we assessed whether the effect of hypnoticinduction on the default mode during rest was correlated with its effect on suggestion-induced changes in brain areas asso-ciated with color perception. This analysis was performed by first extracting the signal from a region of interest (5 mmsphere) centered on the peak voxel of deactivation for the high suggestible group during hypnosis when in rest, comparedwith rest when not in hypnosis, using MarsBaR (http://marsbar.sourceforge.net/). With this method, a value was extractedfor each participant, which represented the level of default mode deactivation that occurred with hypnosis during rest. To

104 W.J. McGeown et al. / Consciousness and Cognition 21 (2012) 100–116

get the other set of values needed for the correlation analysis, a first level analysis was required which examined the differ-ence between hypnosis and no hypnosis conditions when engaging in the color adding task for each participant ([hypnosisadd–hypnosis look]–[no hypnosis add–no hypnosis look]). Due to the nature of the 1st level model specification for thatanalysis, the resulting contrast images had to be masked to ensure that only the brain regions activated by the high suggest-ible participants during hypnosis were specified. The earlier described random effects analysis of the high suggestibleparticipants performing the color adding task when in hypnosis was used as the mask. The default mode ROI values werethen correlated with the masked contrast images from the latter set of analyses.

Unless stated otherwise for all of the analyses the height threshold of significance was set at p < .05 (the type of correctionis specified in the tables). For the interactions a height threshold of p < .01 was used (the type of correction is again specifiedin the tables). Any p-values reported at the voxel level were taken from regions identified a priori only (with an extent size ofgreater than 10 voxels). Anatomical regions were identified using the Talairach Daemon Client (http://www.talairach.org/)(Lancaster et al., 1997, 2000), following conversion of the Montreal Neurological Institute coordinates extracted from theSPM analyses into Talairach coordinates. For all fMRI analyses that are reported in the paper, statistical tables of the results(not present in the article), are available as Supplementary Material Online.

3. Results

3.1. Behavioral data

3.1.1. Hypnotic state reportsWhen out of hypnosis, both high and low suggestible participants reported that they were either in a normal awake state

or very relaxed (M = 1.22, SD = 0.44, and M = 1.29, SD 0.49, for highs and lows respectively). After hypnotic induction threehighs reported being relaxed and eight reported being mildly or deeply hypnotized (M = 3.00, SD = 0.83), whereas lows ratedthemselves as being either relaxed or in a normal awake state (M = 1.57, SD = 0.53). Wilcoxon signed ranks tests revealed asignificant difference in rating before versus after hypnosis in the high suggestible participants (Z = 2.68, p < .01), but not inthe low suggestible participants (Z = 1.41, ns), indicating that the induction of hypnosis produced a self-reported hypnoticstate in high suggestible people only, and it did so only in response to the induction. Thus, the administration of the coloraltering suggestions without a hypnotic induction did not produce the experience of a hypnotic state in any of the partici-pants. This latter finding is consistent with data reported by Mazzoni et al. (2009).

3.1.2. Color perceptionA 2 � 2 � 2 (suggestibility by task by induction) mixed model analysis of variance (ANOVA) carried out on the behavioral

ratings of perceived color revealed a significant main effect for task, F(1,15) = 10.09, p = .006, g2 = .40, qualified by a signif-icant suggestibility by task interaction, F(1,15) = 35.18, p < .001, g2 = .70, and a significant 3-way interaction, F(1,15) = 6.62,p = .021, g2 = .31. The 3-way interaction is depicted in Fig. 2. Post-hoc analyses of the 3-way interaction were conducted byexamination of 95% confidence intervals. When trying to drain color from the color pattern and add color to the greyscalepattern, low suggestible participants saw more color in the color pattern than in the greyscale pattern, and the induction

Fig. 2. Mean self-report ratings for high and low suggestible participants for each of the hallucination tasks in and out of hypnosis. Within-subject errorbars were calculated using the method outlined by Loftus and Masson (1994).

Fig. 3. Brain regions associated with viewing real color. Crosshairs are centred on the left fusiform region (Talairach co-ordinates-26, -68, -8), Brodmann’sarea 19 (part of V4). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Table 1The 2 � 2 ANOVA for the add color task, showing (a) the main effect of group, (b) the main effect of hypnotic induction, (c) the interaction between group (high/low suggestible) and hypnotic induction (with/without) and (d) a paired samples t-test comparing hypnosis to no hypnosis in the high suggestible participants(masked with the results of the interaction). Some regions in the tables are part of the same clusters and therefore do not have a separate voxel count andsignificance level.

Brain area–Brodmannarea (BA)

Left/right Number of voxelsin cluster

Cluster-level p-value(corrected)

Z value at localmaximum

Talairach coordinates

x y z

Panel (a)Main effect of group [add color–look grey]Postcentral Gyrus (BA 3) R 9752 .000 4.24 48 �21 40Postcentral Gyrus (BA 2) R 4.01 53 �21 45Postcentral Gyrus (BA 5) R 3.97 34 �44 56Superior Occipital Gyrus (BA 19) R 3.56 36 �84 21Fusiform Gyrus (BA 37) R 3.38 51 �61 �12Fusiform Gyrus (BA 20) R 3.00 32 �42 �15Inferior Occipital Gyrus (BA 18) R 2.99 44 �74 2Fusiform Gyrus (BA 19) R 2.87 32 �63 �7Lingual Gyrus (BA 18) R 2.86 30 �70 �8Lingual Gyrus (BA 19) R 2.84 30 �62 �4

Middle Frontal Gyrus (BA 6) R 4053 .018 3.65 36 4 40Middle Frontal Gyrus (BA 9) R 3.50 51 7 27

Precuneus (BA 19) L 5708 .002 3.64 �26 �74 30Middle Occipital Gyrus (BA 18) L 3.33 �40 �87 12Inferior Temporal Gyrus (BA 19) L 3.18 �48 �70 0Fusiform Gyrus (BA 19) L 1.68 �26 �68 �8

Panel (b)Main effect of hypnosis [add color–look grey]Lingual Gyrus (BA 18) R 1666 .012* 3.57 �6 �86 �2Lingual Gyrus (BA 18) L 2.98 �2 �76 �1Cuneus (BA 18) R 2.95 14 �99 10

Panel (c)Interaction between group and hypnotic induction [add color–look grey]Cuneus (BA 18) L 64 .002# 2.91 �16 �102 11Middle Occipital Gyrus (BA 18) L .009# 2.37 �18 -95 8

Cuneus (BA 18) R 141 .002# 2.91 10 �99 10Middle Occipital Gyrus (BA 18) R .003# 2.79 20 �98 18Lingual Gyrus (BA 18) R .004# 2.63 20 �97 �2

Panel (d)High suggestible with hypnosis–no hypnosis [add color–look grey] (masked with results of interaction)Cuneus (BA 18) R 132 .000# 3.99 12 �99 10

Cuneus (BA 18) L 61 .001# 3.22 �14 �103 9

Note: Separate clusters are distinguished by blank rows in the table.* p-Values at uncorrected cluster level.

# p-Values at voxel level.

W.J. McGeown et al. / Consciousness and Cognition 21 (2012) 100–116 105

Fig. 4. (a) Brain areas associated with the main effect of group from the ANOVA analysis on the contrast images from the color adding task. (b) Theinteraction between suggestibility (high/low) and hypnotic induction (with/without) on the color adding task. The results of the analyses are shown in red.The brain areas from the earlier analysis to define regions used in viewing color (view color versus view grey) are shown in green. The overlap can be seen inyellow. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 5. Random effects analyses showing (a) the pattern of activation when viewing color was compared to viewing grey, and the activated regions whenadding color to the grey pattern was compared to viewing a grey pattern for (b) the high suggestible people without the hypnotic induction, (c) the highsuggestible people with the hypnotic induction, (d) the low suggestible people without the hypnotic induction, and (e) the low suggestible people with thehypnotic induction. Regions in yellow represent activation cluster corrected, whereas activation in red represents activation not surviving this correction.While performing the color adding task, activation can be seen in the high suggestible people in the fusiform and lingual gyri, bilaterally, with or withoutthe hypnotic induction. Activation is absent in these regions in the low suggestible people both with and without the hypnotic induction. Crosshairs arecentred on the left fusiform region (Talairach co-ordinates-26, -68, -8), Brodmann’s area 19 (part of V4). (For interpretation of the references to color in thisfigure legend, the reader is referred to the web version of this article.)

106 W.J. McGeown et al. / Consciousness and Cognition 21 (2012) 100–116

of hypnosis failed to significantly affect this result, thus failing to show any significant response to either hypnosis or sug-gestion. In contrast, highly suggestible participants in hypnosis saw significantly more color in the greyscale pattern than inthe color pattern, thereby indicating that the effects of the suggestions were stronger than the effects of the stimuli. Whenperforming the add and drain tasks out of hypnosis these participants saw as much color in the greyscale pattern as in thecolor pattern, thus indicating the effectiveness of add and drain suggestions even without hypnosis.

Correlation analyses on the color adding task showed that the deeper the self-reported level of hypnosis experiencedduring the hypnosis trials, the more color was reported in both the hypnosis condition (r = .69, p < .01) and the no hypnosiscondition (r = .55, p < .05). Similarly, on the color draining task, c the deeper the self-reported level of hypnosis, the less colorwas reported in both the hypnosis condition (r = �.74, p < .01) and the no hypnosis condition (r = �.56, p < .05).

Table 2The areas in which a positive correlation was found between activation during the add color task and the ratings of color perception provided by theparticipants when (a) in the hypnosis condition, (b) in the no hypnosis condition. The areas with a positive correlation between the depth of hypnosis achievedin the hypnosis condition only and the activation on the add color task when performed (c) in hypnosis and (d) out of hypnosis. Some regions in the tables arepart of the same clusters and therefore do not have a separate voxel count and significance level.

Brain area –Brodmannarea (BA)

Left/right Number of voxels in cluster Cluster-levelp-value (uncorrected)

Z value atlocal maximum

Talairach coordinates

x y z

Panel (a)Areas that increase in activation with higher ratings of color perception (with hypnosis)Inferior Frontal Gyrus (BA 47) L 894 .032 3.00 �50 27 �1Middle Frontal Gyrus (BA 47) L 2.96 �48 37 �2Inferior Frontal Gyrus (BA 45) L 2.73 �55 22 8Middle Occipital Gyrus (BA 19) R 162 .006# 2.50 32 �83 17

Middle Occipital Gyrus (BA 19) L 61 .012# 2.25 �36 �89 10

Middle Occipital Gyrus (BA 18) L .038# 1.78 �30 �95 12

Inferior Occipital Gyrus (BA 19) R 41 .012# 2.24 42 �78 �1

Lingual Gyrus (BA 18) R 59 .015# 2.18 18 �78 1

Fusiform Gyrus (BA 19) R 83 .017# 2.13 34 �63 �10

Cuneus (BA 7) L 121 .018# 2.09 �24 �78 30Cuneus (BA 18) L .021# 2.04 �18 �84 21

Cuneus (BA 18) R 11 .023# 2.00 16 �100 12

Middle Occipital Gyrus (BA 37) R 33 .028# 1.91 40 �62 1

Lingual Gyrus (BA 18) L 11 .031# 1.86 �16 �82 �6

Panel (b)Areas that increase in activation with higher ratings of color perception (without hypnosis)Precuneus (BA 7) R 1094 .023 3.48 16 �66 40Postcentral Gyrus (BA 5) R 2.20 36 �40 59

Middle Frontal Gyrus (BA 6) R 999 .029 3.32 38 6 44Inferior Frontal Gyrus (BA 9) R 3.06 50 5 26

Claustrum 1137 .021 2.58 36 �10 �10

Middle Temporal Gyrus (BA 39) R 860 .041 2.59 53 �66 11Middle Temporal Gyrus (BA 37) R 2.40 50 �58 3Fusiform Gyrus (BA 37) R 1.73 44 �61 �9

Panel (c)Color adding task activation in hypnosis positively correlated with self-reported hypnotic depth (in hypnosis)Inferior Frontal Gyrus (BA 45) L 1850 .004 3.11 �46 21 3Superior Temporal Gyrus (BA 38) L 3.10 �46 3 �12Insula (BA 13) L 2.93 �42 �6 �1

Middle Occipital Gyrus (BA 19) L 737 .048 3.01 �40 �89 4Middle Occipital Gyrus (BA 18) L 2.97 �36 �89 12

Panel (d)Color adding task activation without hypnosis positively correlated with self-reported hypnotic depth (in hypnosis)Middle Occipital Gyrus (BA 18) L 32 .019# 2.07 �40 �87 12

Inferior Occipital Gyrus (BA 19) L 92 .036# 1.80 �34 �78 �1

Note: Separate clusters are distinguished by blank rows in the table.# p-Values at voxel level.

W.J. McGeown et al. / Consciousness and Cognition 21 (2012) 100–116 107

3.2. fMRI data

3.2.1. Seeing colorTo identify regions of the brain used when veridically viewing color, the contrast images of the color versus greyscale look-

ing comparison were entered in a random effect analysis. Both the scans collected with and without the hypnotic inductionwere used. Significant activation was seen in visual areas including the left lingual gyrus, the left middle occipital gyrus, andthe cuneus and fusiform gyrus, bilaterally (see Fig. 3).

3.2.2. Adding colorThe contrast images obtained in the first level analysis for the add color to greyscale comparison were entered in a 2

(high/low suggestible) � 2 (hypnosis/no hypnosis) ANOVA. There was a main effect of suggestibility with high suggestibleparticipants showing significantly higher activation in a number of visual areas including the left middle occipital gyrus,

Fig. 6. (a) The correlation between lower activity in the default mode network during rest (when hypnosis is compared with no hypnosis) and the activityon the task to hallucinate color (hypnosis versus no hypnosis). (b) Plot of the correlation taken from the peak voxel in the left lingual gyrus.

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the right lingual gyrus, and the fusiform gyrus, bilaterally (for full details see Table 1a, Fig. 4a). There was also a main effect ofhypnosis, with significantly higher activation in hypnosis observed in the right cuneus and in the lingual gyrus, bilaterally(see Table 1b). A significant group by condition interaction was present in the right lingual gyrus, and in the middle occipitalgyrus and cuneus, bilaterally (see Table 1c, Fig. 4b). To clarify the results of the interaction a paired samples t-test was carriedout comparing the hypnosis to the no hypnosis conditions in the high suggestible participants. This analysis was inclusivelymasked with the results from the interaction. The analysis showed that during hypnosis the high suggestible participantshad greater levels of activation in the cuneus bilaterally (see Table 1d). Additional individual group random effects analyseswere also carried out to gain a full understanding of brain regions activated in each of the groups, in and out of hypnosis.Fig. 5 displays these results.

Individual contrast images obtained from first level analysis of all participants when adding color in hypnosis wereentered in a correlation analysis to investigate the link between changes in the blood oxygenation level dependent (BOLD)signal while doing this task in hypnosis and subjective ratings of the intensity of color perceived. The more color participantsreported perceiving, the greater the activation in the left inferior and middle frontal gyri. Significant correlation at the voxellevel was also found in the right inferior occipital and fusiform gyri, and in the cuneus, middle occipital gyrus, and lingualgyrus, bilaterally (Table 2a). A similar correlation analysis was also carried out with the individual contrast images obtainedin the same condition out of hypnosis (Table 2b). The findings showed that as participants’ color ratings increased, activation

Fig. 7. (a) The brain areas associated with the main effect of group (from the ANOVA on the color drain versus color look contrast images). The areas that havesignificantly higher activation in the high suggestible people versus the low suggestible people are shown in red. The areas shown in blue correspond to theadditional ANOVA on the color look versus color drain contrast images. These are the regions that have significantly lower activation in the high suggestibleparticipants than the low suggestible participants when performing the color draining task. (b) Areas in red illustrate those with a significant interactionbetween suggestibility (high/low) and hypnotic induction (with/without) on the color draining task (using the color drain versus color look contrast images).The blue areas correspond to the interaction between group and hypnotic induction on the other ANOVA (using the color look versus color drain contrastimages). The brain areas from the earlier analysis to identify the regions used in viewing color are shown in green in both parts of the figure. The overlapbetween this analysis and the regions of deactivation in both parts of the figure can be seen in light blue. (For interpretation of the references to color in thisfigure legend, the reader is referred to the web version of this article.)

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also increased in the right fusiform gyrus, middle temporal gyrus, precuneus, postcentral gyrus, inferior frontal and middlefrontal gyri and claustrum.

Correlations of subjective ratings of depth of hypnosis with changes in activation during the color adding task showedthat in the hypnosis condition activation increased in the left middle occipital gyrus, inferior frontal gyrus, superior temporalgyrus and insula, as subjective depth of hypnosis scores increased (Table 2c). Correlating the depth of hypnosis that eachparticipant reported in the hypnosis condition with the ratings with the data from the color adding task collected whileparticipants were out of hypnosis, did not reveal any significant associations at either the corrected or uncorrected clusterlevel, however at the voxel level significant correlations were seen in the left inferior and middle occipital gyrus (Table 2d).

In a previously published article (McGeown et al., 2009), we reported alterations in brain activity during rest in highsuggestible individuals. These changes consisted of reductions in activity in brain structures in part of the anterior defaultmode network of the brain while following hypnosis. It follows that there might be a relationship between reductions inanterior default mode network in hypnosis and modulation of activity while individuals were trying to add color to a grey-scale pattern. To test this hypothesis a further correlation analysis was carried out between activity differences during rest inand out of hypnosis and activity difference again in and out of hypnosis when participants were trying to add color to thegreyscale pattern. Voxels of significant correlations were found in the right middle occipital gyrus, and the cuneus andlingual gyrus bilaterally (see Fig. 6a and b). It appears, therefore, that the greater the level of deactivation during rest in hyp-nosis, the greater the level of activation detected in these visual areas during the color adding condition in hypnosis.

3.2.3. Draining colorA parallel set of analyses to those carried out for the adding color condition were also carried out for the draining color

conditions. Individual contrast images obtained at first level analysis comparing the draining color conditions to seeing colorwere entered in a 2 � 2 ANOVA with suggestibility (high/low) and hypnosis (present/absent) as main factors. There was asignificant main effect of suggestibility, with significantly higher levels of activation in high than in low suggestible peoplein the right inferior frontal gyrus, superior parietal lobule, precuneus, cuneus and fusiform gyrus (Fig. 7a and Table 3a). Therewas also a main effect of hypnosis, with a higher level of activation in the hypnosis condition being detected bilaterally inregions such as the anterior cingulate gyrus, hippocampus, insula, caudate nucleus, amygdala and lentiform nucleus (Table3b). A significant group by condition interaction was found in the right fusiform gyrus and the middle occipital gyrus, bilat-erally (Fig. 7b and Table 3c).

Table 3The 2 � 2 ANOVA for the color draining task showing the (a) the main effects of group, (b) the main effects of hypnosis, (c) the interactions between group(high/low suggestible) and hypnotic induction (with/without) for the drain versus look contrast images, (d) a paired samples t-test comparing hypnosis to nohypnosis in the high suggestible participants (masked with the results of the interaction).

Brain area–Brodmann area (BA) Left/right Number of voxelsin cluster

Cluster-level p-value (corrected) Z value at localmaximum

Talairach coordinates

x y z

Panel (a)Main effect of group [drain color–look color]Inferior Frontal Gyrus (BA 44) R 4959 .003 4.55 50 7 22Inferior Frontal Gyrus (BA 45) R 4.05 51 18 19Inferior Frontal Gyrus (BA 47) R 3.46 38 21 �9

Superior Parietal Lobule (BA 7) R 7674 .000 3.98 22 �57 62Precuneus (BA 19) R 3.94 24 �76 35Cuneus (BA 19) R 3.85 32 �86 28Fusiform Gyrus (BA 37) R 2.06 34 �47 �13

Panel (b)Main effect of hypnosis [drain – look]Insula (BA 13) R 30,650 .000 4.65 38 �16 23Lentiform Nucleus L 4.57 �28 �12 �8Hippocampus R 4.32 34 �20 �11Superior Temporal Gyrus (BA 38) R 4.24 44 �3 �12Precentral Gyrus (BA 6) L 3.98 �51 2 11Insula (BA 13) L 3.92 �30 �11 19Caudate L 3.91 �8 16 8Anterior Cingulate (BA 25) L 3.84 �4 19 �4Precentral Gyrus (BA 44) L 3.83 �44 4 11Hippocampus L 3.78 �34 �11 �16Inferior Frontal Gyrus (BA 47) R 3.72 22 11 �19Caudate R 3.69 20 16 10Claustrum L 3.62 �28 �15 17Posterior Cingulate (BA 31) R 3.61 16 �31 38Anterior Cingulate (BA 24) R 3.56 8 32 11Middle Frontal Gyrus (BA 11) L 3.47 �32 36 �12Anterior Cingulate (BA 32) L 3.45 �12 36 18Amygdala L 3.35 �28 �5 �15Precuneus (BA 7) L 3.31 �8 �31 46Lentiform Nucleus R 3.27 16 5 �7Subcallosal Gyrus (BA 25) R 3.27 10 21 �9Amygdala R 3.23 32 �7 �16

Panel (c)Interaction between group and hypnotic induction [drain–look]Middle Occipital Gyrus (BA 19) R 341 .019* 3.84 38 �87 17Middle Occipital Gyrus (BA 18) R 3.20 44 �83 1

Fusiform Gyrus (BA 19) R 133 .001# 3.04 34 �78 �10

Middle Occipital Gyrus (BA 19) L 119 .003# 2.88 �30 �83 13Middle Occipital Gyrus (BA 18) L 2.80 �36 �93 3

Panel (d)High suggestible with hypnosis–without hypnosis [drain–look] (masked with results of the interaction)Middle Occipital Gyrus (BA 19) R 80 .004# 2.69 38 �87 17Middle Occipital Gyrus (BA 18) R .009# 2.37 32 �93 10

Middle Occipital Gyrus (BA 18) L 14 .023# 1.99 �36 �93 3Inferior Occipital Gyrus (BA 18) L .034# 1.83 �32 �97 �2

Note: Separate clusters are distinguished by blank rows in the table.* p-Values at uncorrected cluster level.

# p-Values at voxel level.

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To further understand the interaction a paired samples t-test comparing the hypnosis to no hypnosis conditions in thehigh suggestible participants (masked by the results of the interaction) showed greater activity when doing the task underhypnosis in the left inferior occipital gyrus and the middle occipital gyrus bilaterally (Table 3d). The results of the individualrandom effects analyses for each group in and out of hypnosis can be seen in Fig. 8.

To better investigate possible deactivations in the draining color task, a second 2 (high/low suggestibility) � 2 (hypnosis/no hypnosis) ANOVA was carried out using the individual contrast images obtained from contrasting the look versus draintasks. There was a main effect of suggestibility, with high suggestible participants deactivating bilateral primary visualregions and the posterior cingulate gyrus (Fig. 7a and Table 4a) more than low suggestible people. The main effect of hyp-

Fig. 8. Random effects analyses showing (a) the pattern of activation when viewing color was compared to viewing grey, and the significant differenceswhen the draining color condition was compared to the viewing of a color pattern for (b) the high suggestible people without the hypnotic induction, (c) thehigh suggestible people with the hypnotic induction, (d) the low suggestible people without the hypnotic induction, and (e) the low suggestible people withthe hypnotic induction. Regions in yellow represent activation cluster corrected, whereas activation in red represents activation not surviving thiscorrection. Regions in blue represent deactivation (e.g., the difference between looking at a color pattern versus draining color from a color pattern) at thecluster corrected threshold of significance. Crosshairs are centred on the left fusiform region (Talairach co-ordinates-26, -68, -8), Brodmann’s area 19 (partof V4). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

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nosis did not survive cluster correction, but there were significant decreases at the voxel level in visual areas such as the leftlingual gyrus and the fusiform gyrus and middle occipital gyrus bilaterally (Table 4b). A significant suggestibility (high/low) � hypnosis (present/absent) interaction was observable in the right posterior cingulate gyrus and the anterior cingulategyrus bilaterally (Fig. 7b and Table 4c). A paired samples t-test comparing the hypnosis to no hypnosis conditions in the highsuggestible participants (masked by the results of the interaction) showed greater deactivation in while under hypnosis in anumber of regions in the default mode network (Table 4d). See Fig. 8 for the random effects analyses of each group in and outof hypnosis.

Correlation analyses were carried out to clarify whether the changes in BOLD signal detected in the color draining con-dition were correlated with subjective ratings of intensity of color perceived. In the hypnosis condition lower intensity ofperceived color (successful draining) was negatively correlated with levels of activation in the right middle and inferioroccipital gyri, the inferior parietal lobule and the inferior frontal gyrus (Table 5a). There were also some clusters in whicha significant positive correlation (i.e., lower intensity of color perceived correlating with lower level of brain activity) wasfound in the left inferior parietal lobule, middle temporal gyrus, posterior cingulate gyrus, the right precentral gyrus and par-acentral lobule, the right superior temporal gyrus, and the insula bilaterally (Table 5a).

Subjective depth of hypnosis ratings were significantly correlated with higher levels of activation in visual areas such asthe right inferior and middle occipital gyri (Table 5b). Areas of significant correlation at the voxel probability level werefound in the inferior and occipital gyri, lingual gyrus, and precuneus in the left hemisphere, and in the fusiform gyrus, bilat-erally. Significant associations were also seen between deeper reported levels of hypnosis and decreases in activation in theleft anterior cingulate gyrus, medial frontal gyrus, inferior parietal lobule and postcentral gyrus and in the superior temporalgyrus, bilaterally (Table 5b).

4. Discussion

In this brain imaging study, the effects of hypnosis on suggestions for alterations in color perception were investigated inhigh and low suggestible people. More specifically, we sought to address the questions of whether the induction of a hyp-notic state is necessary for experiencing suggestions for perceptual alterations, as reflected by changes in activation in areasof the visual cortex associated with color perception, and whether, if not necessary, it nevertheless enhances responsivenessto these suggestions. To answer these questions, we assessed whether self reports of visual alterations of perception areaccompanied by changes in color-responsive areas of the visual cortex and whether the changes in the visual experience pro-duced by the induction of hypnosis are associated with unique alterations in brain activation. Our results indicate that theinduction of hypnosis is not necessary for the self-report of suggested perceptual alterations or for the changes in corticalactivity that are associated with those self-reported experiences. However, hypnotic induction enhanced experientialchanges in color and the level of activation in associated cortical areas.

Table 4The 2 � 2 ANOVA for the color draining task showing the (a) the main effects of group, (b) the main effects of hypnosis, (c) the interactions between participant(high/low suggestible) and hypnotic induction (with/without) for the look versus drain contrast images, (d) a paired samples t-test comparing hypnosis to nohypnosis in the high suggestible participants (masked with the results of the interaction).

Brain area–Brodmannarea (BA)

Left/right Number ofvoxels in cluster

Cluster-levelp-value (corrected)

Z value at localmaximum

Talairach coordinates

x y z

Panel (a)Main effect of group [look color–drain color]Cuneus (BA 18) L 5284 .002 3.77 �10 �87 15Cuneus (BA 19) L 3.74 �10 �80 35Cuneus (BA 17) L 3.13 �20 �73 11Cuneus (BA 30) R 3.00 20 �71 11Cuneus (BA 30) L 2.84 0 �71 9Lingual Gyrus (BA 18) R 2.78 8 �54 3Posterior Cingulate (BA 30) L 2.78 �20 �62 9Middle Occipital Gyrus (BA 18) L 2.78 �22 �101 9Posterior Cingulate (BA 30) R 2.76 24 �62 7Cuneus (BA 18) R 2.74 12 �73 17Cuneus (BA 19) R 2.72 16 �84 37Lingual Gyrus (BA 19) L 2.68 �8 �64 2Lingual Gyrus (BA 19) R 2.63 10 �62 1Cuneus (BA 17) R 2.55 8 �79 6Precuneus (BA 7) R 2.54 8 �74 37Parahippocampal Gyrus (BA 30) R 2.43 14 �43 0Posterior Cingulate (BA 29) R 2.34 6 �44 6Posterior Cingulate (BA 29) L 2.31 �2 �46 6

Panel (b)Main effect of hypnosis [look–drain]Fusiform Gyrus (BA 19) R 385 .003# 2.75 24 �63 �10Middle Occipital Gyrus (BA 18) R .004# 2.64 30 �78 �6Fusiform Gyrus (BA 37) R .016# 2.13 40 �53 �12

Lingual Gyrus (BA 19) L 248 .005# 2.60 �26 �70 �3Lingual Gyrus (BA 18) L .005# 2.55 �22 �80 �3Fusiform Gyrus (BA 19) L .016# 2.14 �28 �65 �10

Middle Temporal Gyrus (BA 39) L 284 .006# 2.50 �51 �65 12Middle Occipital Gyrus (BA 19) L .016# 2.14 �55 �70 7Angular Gyrus (BA 39) L .017# 2.12 �46 �69 27

Panel (c)Interaction between group and hypnotic induction [look–drain]Cingulate Gyrus (BA 31) R 1466 .001 5.02 12 �27 36Precuneus (BA 7) L 4.23 �8 �31 46Cingulate Gyrus (BA 24) L 3.58 �10 �19 38

Superior Temporal Gyrus (BA 38) R 2620 .000 4.70 40 1 �14Claustrum R 4.28 38 �6 �5Brainstem L 3.90 0 �25 0

Superior Temporal Gyrus (BA 42) L 599 .003* 3.87 �63 �30 16Inferior Parietal Lobule (BA 40) L 3.42 �59 �35 31

Anterior Cingulate (BA 24) R 580 .004* 3.38 8 30 11Anterior Cingulate (BA 33) L 3.33 �4 20 17Anterior Cingulate (BA 24) L 3.23 �6 28 15

Precentral Gyrus (BA 6) R 270 .034* 3.22 53 �5 9Postcentral Gyrus (BA 2) R 3.13 46 �18 29Precentral Gyrus (BA 4) R 2.98 40 �16 36

Panel (d)High suggestible with hypnosis–without hypnosis [look–drain] (masked with results of the interaction)Anterior Cingulate Gyrus (BA 24) L 327 .002# 2.96 �10 �19 38Posterior Cingulate Gyrus (BA 23) R .002# 2.89 6 �33 29Posterior Cingulate Gyrus (BA 31) R .003# 2.75 10 �27 36

Medial Frontal Gyrus (BA 6) R 13 .006# 2.50 6 �19 53

Inferior Parietal Lobule (BA 40) L 22 .008# 2.42 �53 �42 46

Medial Frontal Gyrus (BA 9) R 17 .015# 2.17 6 38 31

Note: Separate clusters are distinguished by blank rows in the table.* p-Values at uncorrected cluster level.

# p-Values at voxel level.

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Table 5The areas in which the level of activation (during the color draining task) correlates significantly with (a) the ratings of color perception provided by theparticipants when in the scanner in the hypnosis condition, and (b) the ratings of the depth of hypnosis that was experienced in the scanner. Some regions inthe tables are part of the same clusters and therefore do not have a separate voxel count and significance level.

Brain area–Brodmann area (BA) Left/right Number of voxelsin cluster

Cluster-level p-value (corrected) Z value at localmaximum

Talairach coordinates

x y z

Panel (a)Areas that increase in activation with lower ratings of color perceptionMiddle Occipital Gyrus (BA 18) R 2282 .001* 3.65 32 �93 10Inferior Occipital Gyrus (BA 17) R 3.49 20 �92 �7Inferior Parietal Lobule (BA 7) R 3.21 40 �64 47

Inferior Frontal Gyrus (BA 46) R 1054 .018⁄ 3.25 50 47 1Inferior Frontal Gyrus (BA 44) R 2.98 51 5 22

Areas that decrease in activation with lower ratings of color perceptionInferior Parietal Lobule (BA 40) L 3511 .009 4.86 �57 �44 21Middle Temporal Gyrus (BA 39) L 3.83 �46 �63 18Insula (BA 13) L 3.82 �40 �16 �8

Posterior Cingulate (BA 31) L 8264 .000 4.82 �16 �29 42Precentral Gyrus (BA 4) R 4.43 36 �15 50Paracentral Lobule (BA 5) R 4.29 12 �35 48

Superior Temporal Gyrus (BA 22) R 2422 .001* 3.89 67 �32 11Insula (BA 13) R 3.25 40 �30 20

Panel (b)Areas that increase in activation due to increased hypnotic depthInferior Occipital Gyrus (BA 18) R 969 .025* 2.90 22 �90 �7Middle Occipital Gyrus (BA 19) R 2.59 28 �85 8Middle Occipital Gyrus (BA 18) R 2.42 32 �80 �9

Fusiform Gyrus (BA 37) R 309 .001# 3.28 26 �49 �13

Fusiform Gyrus (BA 37) L 586 .001# 3.09 �34 �55 �11Lingual Gyrus (BA 17) L .002# 2.84 �16 �87 1Inferior Occipital Gyrus (BA 18) L .003# 2.75 �26 �86 �6Middle Occipital Gyrus (BA 19) L 609 .002# 2.86 �32 �91 16Precuneus (BA 19) L .006# 2.52 �22 �76 33

Panel (c)Areas that decrease in activation due to increased hypnotic depthMedial Frontal Gyrus (BA 6) L 3936 .006 4.15 6 �7 50Anterior Cingulate (BA 24) L 3.93 4 26 6

Superior Temporal Gyrus (BA 22) R 1385 .009⁄ 3.82 59 �23 5Middle Temporal Gyrus (BA 21) R 3.07 57 �24 �4

Superior Temporal Gyrus (BA 22) L 1586 .006* 3.52 �61 �40 22Postcentral Gyrus (BA 40) L 3.04 �63 �26 18Inferior Parietal Lobule (BA 40) L 2.87 �53 �28 24

Note: Separate clusters are distinguished by blank rows in the table.* p-Values at uncorrected cluster level.

# p-Values at voxel level.

W.J. McGeown et al. / Consciousness and Cognition 21 (2012) 100–116 113

The results of this study confirm previous findings indicating that, when reporting changes in color perception, high sug-gestible individuals concomitantly modulate the neural activation of color-related areas in the brain, such as the fusiformgyrus, bilaterally (Kosslyn et al., 2000), and primary visual areas. Kosslyn et al. (2000) reported changes in the right fusiformarea both in and out of hypnosis, but significant changes in the left fusiform area only when participants had been hypno-tized. The absence of left fusiform activation when out of hypnosis was the basis for their claim that altered perceptionoccurred only when the suggestion was given during hypnosis.

In the present study, the lack of interaction with the induction of hypnosis in fusiform areas bilaterally during the coloradding task suggests that suggestibility, rather than hypnosis per se, is responsible for the patterns of activation observed inthe brain in this task. While the suggestion provided by Kosslyn et al. (2000) was worded differently in the hypnosiscondition than in the no-hypnosis condition, in the present study we gave the same instruction to participants in both con-ditions. Kosslyn et al.’s stated reason for changing wording of the suggestion was their concern that subjects might ‘‘fall intoa hypnotic state during performance of the task (p. 1281),’’ despite the absence of an induction, if the same wording wereused. We have previously shown that people do not slip into a hypnotic state, as judged either by their self report (Mazzoniet al., 2009, and in the present study) or by changes in activation in the default mode network (McGeown et al., 2009), whengiven the color-changing suggestions without a hypnotic induction. Thus, our finding of bilateral changes in fusiform areas

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without an interaction should be taken as indicating that in highly suggestible individuals, perception is changed by sugges-tion both in and out of hypnosis.

The hypnotic state thus seems not to be crucial in experiencing suggested hallucinations, and it might be a product ofsuggestion that has limited relation to the experience of other suggested phenomena (Kihlstrom, 1985; Kirsch, 2011; Wag-staff, 1998).

Although according to our data, suggestibility rather than hypnosis is the primary factor responsible for perceptual alter-ations of color, we also found a significant interaction in visual areas other than the fusiform gyrus, such as the middle occip-ital gyrus, bilaterally, both when adding and when draining color. At least in visual tasks, there is activation in visual areaswhich is specifically linked to the induction of hypnosis, a result which is in accord with the small enhanced effect ofhypnosis obtained in the behavioral data. The significant enhancement due to the induction of hypnosis is also revealedby the correlation between a lower default mode activity at rest in hypnosis and the ability of hypnosis to further activatevisual areas of the brain during the color adding task. In other words, the more participants actively engaged in the hypnoticprocedure, the more successful they were at seeing color on the color adding task. It seems, then, that the induction of hyp-nosis is linked to the brain activation of specific areas that are mainly related to the suggested task and to the modulation ofattention (for a review see Oakley, 2008; Oakley & Halligan, 2009).

Next we discuss the results of the two visual tasks in greater detail.

4.1. Color adding suggestion

Only highly suggestible participants reported seeing color both in and out of hypnosis when looking at the grey stimulus,and hypnosis slightly enhanced their experience. Investigating the patterns of brain activation on the task showed that theseindividuals also had extensive differences in extrastriate color sensitive areas when compared to low suggestible individuals,regardless of the presence of hypnosis. When they reported seeing color while looking at the grey pattern, activation oc-curred in visual regions that overlap with the color regions identified in the current study during the veridical viewing ofcolor, and with regions (e.g., the left fusiform region) identified in the literature on color perception (e.g., Zeki et al.,1991). The primary role of suggestibility was further confirmed by the significant positive correlations that were presentboth in and out of hypnosis, between the self-reported depth of hypnosis and the self-reported color perception ratings,as well as between the self-reported depth of hypnosis and the level of activity in the left middle occipital gyrus.

Taken together, these data indicate that the ability to respond to imaginative suggestions (i.e., primary suggestibility) isassociated with color altering abilities in general, and not specifically when under hypnosis. However, the induction ofhypnosis did appear to significantly enhance behavioral responsiveness to the add color suggestions in high suggestible indi-viduals. The enhancement due to the hypnotic induction is also evident when considering the interaction showing greateractivation in some visual areas in high suggestible individuals when in hypnosis compared to being out of hypnosis, whereasin low suggestible individuals hypnosis had no effect.

4.2. Color draining suggestion

Only high suggestible participants reported seeing less color in the color stimulus during the drain task, and hypnosisslightly enhanced their experience. Whereas the pattern of brain activation involving the color adding suggestion seemedto be clear and easily interpretable, a complex pattern of brain activity was identified for the successful completion of thecolor draining task. This involved activation in extrastriate visual areas and deactivation in regions which included theprimary visual cortex. This pattern of results could be seen in high suggestible participants, while performing the task inor out of hypnosis.

In addition to greater activation in the visual areas, high suggestible participants had significantly higher activation thanlow suggestible people in right frontal and parietal regions, which might coincide with greater attentional recruitment. Pre-vious neuroimaging studies have reported the activation of a similar right frontal–parietal network in response to attentionaltasks (e.g., Pardo, Fox, and Raichle (1991), Posner and Raichle (1997)).

The interaction between suggestibility and the induction of hypnosis indicated greater activation in areas associated withvision (e.g., the right fusiform gyrus and the middle occipital gyrus, bilaterally), areas that in part overlap with thoseobtained in the color adding task. We cannot infer with certainty why these areas are activated rather than deactivated whenhigh suggestible participants are draining color in hypnosis. It could be that the activation of the right fusiform region is asso-ciated with mental imagery (Howard et al., 1998; Kosslyn et al., 2000), while the activation of middle occipital gyri might bedue to seeing fluctuations or changes in color or pattern of the stimulus.

The look versus drain comparison also indicated that high suggestible participants showed greater levels of deactivationthan low suggestible participants in the primary visual cortex during the color draining task. Thus, in the processing streamof visual information, areas that receive visual information early seemed to be significantly reduced in activity and, presum-ably, functionality. A significant interaction was also detected in parts of the anterior and posterior cingulate, which appearsto reflect a greater decrease in default mode activity that occurs in high suggestible participants in hypnosis when engagingin color draining. This could be indicative of greater effort by the high suggestible participants when provided with a hyp-notic induction, or it may suggest that greater reduction in default mode activity is a necessary requirement for more effi-cient task performance.

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5. Conclusions

The ability of highly suggestible people to alter color perception revealed in this study appears to be generally consistentwith the results of the color hallucination study carried out by Kosslyn et al. (2000), despite the use of a more stringentexperimental design in our study. When under hypnosis and performing both color alteration tasks, high suggestible partic-ipants modulated activity in a number of visual areas, and alterations in the perception of color were confirmed by the self-report data. Unlike Kosslyn et al., however, we found that highly suggestible participants were able to alter their perceptionof color both in and out of hypnosis, when the exact same suggestion was given in both conditions. Highly suggestibleparticipants did not spontaneously slip into hypnosis, as confirmed by current self-report data, and previous studies on selfreport (Mazzoni et al., 2009), and fMRI data obtained during resting periods between suggestions (McGeown et al., 2009).

We also found evidence that the alterations in default mode brain activity produced by the induction of hypnosis inhighly suggestible individuals were significantly correlated with subsequent differences between responses to suggestionin hypnosis and responses to the same suggestions out of hypnosis. These data are consistent with the hypothesis previouslyproposed (McGeown et al., 2009) that the hypnotic induction may lead highly suggestible participants to focus attention onthe anticipated suggestions, thereby allowing them to make better use of their imaginative skills. This is also consistent withthe hypothesis that there is a hypnotic state in Hilgard’s (1973) sense of the term that enhances the experience of imagina-tive or ‘‘primary’’ suggestions. The specific activation of visual areas and of attentional areas also support this interpretation.

These results clarify the complex interaction between individual characteristics (suggestibility) and the induction ofhypnosis. Both the behavioral and fMRI data in this study reveal the primary role of suggestibility, regardless of the presenceof a hypnotic state, but they also indicate that the induction of hypnosis helps suggestible individuals to better tune atten-tional and task-specific cognitive resources towards the task at hand.

Acknowledgment

We thank the BBC for partially funding this study.

Appendix A. Supplementary material

Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.concog.2011.10.015.

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