Hypnosis decouples cognitive control from conflict monitoring processes of the frontal lobe.
ABSTRACT Hypnosis can profoundly alter sensory awareness and cognitive processing. While the cognitive and behavioral phenomena associated with hypnosis have long been thought to relate to attentional processes, the neural mechanisms underlying susceptibility to hypnotic induction and the hypnotic condition are poorly understood. Here, we tested the proposal that highly hypnotizable individuals are particularly adept at focusing attention at baseline, but that their attentional control is compromised following hypnosis due to a decoupling between conflict monitoring and cognitive control processes of the frontal lobe. Employing event-related fMRI and EEG coherence measures, we compared conflict-related neural activity in the anterior cingulate cortex (ACC) and control-related activity in the lateral frontal cortex (LFC) during Stroop task performance between participants of low and high hypnotic susceptibility, at baseline and after hypnotic induction. The fMRI data revealed that conflict-related ACC activity interacted with hypnosis and hypnotic susceptibility, in that highly susceptible participants displayed increased conflict-related neural activity in the hypnosis condition compared to baseline, as well as with respect to subjects with low susceptibility. Cognitive-control-related LFC activity, on the other hand, did not differ between groups and conditions. These data were complemented by a decrease in functional connectivity (EEG gamma band coherence) between frontal midline and left lateral scalp sites in highly susceptible subjects after hypnosis. These results suggest that individual differences in hypnotic susceptibility are linked with the efficiency of the frontal attention system, and that the hypnotized condition is characterized by a functional dissociation of conflict monitoring and cognitive control processes.
- SourceAvailable from: Andres Canales-Johnson[Show abstract] [Hide abstract]
ABSTRACT: Santiago Ramón y Cajal (1852-1934) did not only contribute to neurobiology and neurohistology. At the end of the 19th century, he published one of the first clinical reports on the employment of hypnotic suggestion to induce analgesia (hypnoanalgesia) in order to relieve pain in childbirth. Today, the clinical application of hypnoanalgesia is considered an effective technique for the treatment of pain in medicine, dentistry, and psychology. However, the knowledge we have today on the neural and cognitive underpinnings of hypnotic suggestion has increased dramatically since Cajal's times. Here we review the main contributions of Cajal to hypnoanalgesia and the current knowledge we have about hypnoanalgesia from neural and cognitive perspectives.Frontiers in Psychology 09/2014; · 2.80 Impact Factor
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ABSTRACT: This study explores whether self-reported depth of hypnosis and hypnotic suggestibility are associated with individual differences in neuroanatomy and/or levels of functional connectivity. Twenty-nine people varying in suggestibility were recruited and underwent structural, and after a hypnotic induction, functional magnetic resonance imaging at rest. We used voxel-based morphometry to assess the correlation of grey matter (GM) and white matter (WM) against the independent variables: depth of hypnosis, level of relaxation and hypnotic suggestibility. Functional networks identified with independent components analysis were regressed with the independent variables. Hypnotic depth ratings were positively correlated with GM volume in the frontal cortex and the anterior cingulate cortex (ACC). Hypnotic suggestibility was positively correlated with GM volume in the left temporal-occipital cortex. Relaxation ratings did not correlate significantly with GM volume and none of the independent variables correlated with regional WM volume measures. Self-reported deeper levels of hypnosis were associated with less connectivity within the anterior default mode network. Taken together, the results suggest that the greater GM volume in the medial frontal cortex and ACC, and lower connectivity in the DMN during hypnosis facilitate experiences of greater hypnotic depth. The patterns of results suggest that hypnotic depth and hypnotic suggestibility should not be considered synonyms. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.Psychiatry Research Neuroimaging 12/2014; · 2.83 Impact Factor
Hypnosis decouples cognitive control from conflict monitoring
processes of the frontal lobe
Tobias Egner,a,*Graham Jamieson,band John Gruzelierc
aFunctional MRI Research Center, Columbia University, Neurological Institute Box 108, 710 West 168th Street, New York, NY 10032, USA
bDepartment of Psychology, University of New England, Armidale, NSW 2351, Australia
cDivision of Neuroscience and Psychological Medicine, Imperial College London, St. Dunstan’s Road, London W6 8RF, UK
Received 13 January 2005; revised 2 May 2005; accepted 3 May 2005
Available online 17 June 2005
Hypnosis can profoundly alter sensory awareness and cognitive
processing. While the cognitive and behavioral phenomena associated
with hypnosis have long been thought to relate to attentional
processes, the neural mechanisms underlying susceptibility to hypnotic
induction and the hypnotic condition are poorly understood. Here, we
tested the proposal that highly hypnotizable individuals are partic-
ularly adept at focusing attention at baseline, but that their attentional
control is compromised following hypnosis due to a decoupling
between conflict monitoring and cognitive control processes of the
frontal lobe. Employing event-related fMRI and EEG coherence
measures, we compared conflict-related neural activity in the anterior
cingulate cortex (ACC) and control-related activity in the lateral
frontal cortex (LFC) during Stroop task performance between
participants of low and high hypnotic susceptibility, at baseline and
after hypnotic induction. The fMRI data revealed that conflict-related
ACC activity interacted with hypnosis and hypnotic susceptibility, in
that highly susceptible participants displayed increased conflict-related
neural activity in the hypnosis condition compared to baseline, as well
as with respect to subjects with low susceptibility. Cognitive-control-
related LFC activity, on the other hand, did not differ between groups
and conditions. These data were complemented by a decrease in
functional connectivity (EEG gamma band coherence) between frontal
midline and left lateral scalp sites in highly susceptible subjects after
hypnosis. These results suggest that individual differences in hypnotic
susceptibility are linked with the efficiency of the frontal attention
system, and that the hypnotized condition is characterized by a
functional dissociation of conflict monitoring and cognitive control
D 2005 Elsevier Inc. All rights reserved.
Keywords: Hypnosis; Cognitive control; Conflict monitoring; Attention;
Within a few minutes of hypnotic induction, some 10–15% of
healthy alert individuals are able to demonstrate profound
alterations in many aspects of their conscious experience
(Hilgard, 1965). In response to suggestion, they may experience
a lack of control over their own actions, the inability to recall
recent events, the absence of pain and other specific sensations,
or conversely the apparent reality of illusory events. These
features of hypnosis are utilized by clinicians to facilitate
therapeutic interventions in diverse areas of psychological
medicine. The effectiveness of incorporating hypnosis in clinical
interventions has gained positive empirical support in pain
control, anxiety, depression, trauma, weight loss, and eating
disorders among other areas (Lynn et al., 2000). The rapid, non-
pathological, and reversible changes in conscious awareness and
cognitive processing encountered in hypnosis also provide an
intriguing domain, as well as a (largely unexploited) tool of
research, in the cognitive neurosciences (Raz and Shapiro, 2002).
For instance, hypnotic manipulation of subjective experience,
such as the processing of pain, in conjunction with current
neuroimaging techniques has helped to dissociate the neural bases
of distinct aspects of sensory and cognitive processes (Halligan et
al., 2000; Rainville et al., 1997). By the same token, advances in
neuroimaging have started to facilitate our understanding of
specific hypnotic manipulations of sensory experience (Kosslyn
et al., 2000; Rainville et al., 1999, 2002; Szechtman et al., 1998).
However, the basic neural mechanisms underpinning the phe-
nomena of hypnosis and hypnotic susceptibility are currently not
Many accounts of hypnosis have proposed that individual
differences in hypnotic susceptibility are related to differences in
executive attentional control. One traditional view has been that
hypnosis itself is characterized by strongly focused attention, and
that hypnotic susceptibility is due to individual differences in the
ability to engage in such focused attention (Barber, 1960; Spiegel,
2003; Tellegen and Atkinson, 1974; cf. Jamieson and Sheehan,
2002). Another account holds that while highly hypnotizable
1053-8119/$ - see front matter D 2005 Elsevier Inc. All rights reserved.
* Corresponding author.
E-mail address: email@example.com (T. Egner).
Available online on ScienceDirect (www.sciencedirect.com).
NeuroImage 27 (2005) 969 – 978
subjects may be exceptionally adept at focusing attention at
baseline, their attentional control is largely compromised follow-
ing hypnotic induction (Crawford and Gruzelier, 1992; Gruzelier,
1990; Hilgard, 1965, 1977; 1998; Woody and Bowers, 1994).
The latter model has received support from a series of studies
showing that participants with high, but not low susceptibility
exhibit impaired attentional control after hypnotic induction, as
evidenced by deteriorated error performance on the Stroop
(MacLeod, 1991; Stroop, 1935) paradigm (Jamieson and Sheehan,
2004; Kaiser et al., 1997; see also Nordby et al., 1999), and
attenuated orienting responses (Gruzelier and Brow, 1985; Gruze-
lier et al., 1988). Support has also been forthcoming from
neuropsychological evidence which, inter alia, has often suggested
that left anterior functions in particular appear to be compromised
during hypnosis in more highly susceptible participants; measures
have encompassed event-related potentials (Jutai et al., 1993),
haptic sorting (Cikurel and Gruzelier, 1990; Gruzelier et al., 1984),
and letter versus category word fluency tasks (Gruzelier and
Warren, 1993; Kallio et al., 2001; cf. Aikins and Ray, 2001). It
should be noted that these observations refer to performance after
generic hypnotic inductions that do not entail specific instructions
aimed at eliminating interference effects. In cases where such
instructions are given, Stroop interference in hypnotic as well as
post-hypnotic performance may be reduced in highly susceptible
individuals (Raz et al., 2002, 2003; Sheehan et al., 1988).
These observations have been tied to neurophysiological
hypotheses relating hypnosis in highly susceptible individuals to
alterations of anterior brain functions such as selective inhibition,
disconnection, and dissociation of the frontal lobe (Gruzelier, 1990,
1998, 2000, 2004), or decoupling between conflict monitoring and
cognitive control functions of the frontal attention system (see
below) (Jamieson and Sheehan, 2004). The current study aimed at
directly testing the merits of the ‘‘focused attention’’ model and the
‘‘impaired attention’’ model of hypnosis at the neural level, by
capitalizing on recent advances in the understanding of the neural
bases of frontal attention processes.
Much recent work on characterizing the functional neuro-
anatomy of attentional control suggests the existence of dissoci-
able sub-processes of conflict monitoring and cognitive control,
performed by the dorsal anterior cingulate cortex (ACC) and
lateral frontal cortex (LFC), respectively (Botvinick et al., 2001;
MacDonald et al., 2000). It has been proposed that the ACC
performs continuous monitoring of potential response conflict
(due to interference or ‘‘crosstalk’’ between different processing
streams), and that in the case of high conflict detection, the LFC
implements cognitive control, resolving conflict by biasing
information processing towards task-relevant properties (Botvi-
nick et al., 2001; for recent reviews, see Botvinick et al., 2004;
Ridderinkhof et al., 2004). An ample body of data from neuro-
imaging studies supports the notion that ACC activation covaries
with levels of response conflict in selective attention tasks, such as
the Stroop paradigm (e.g., Botvinick et al., 1999; Carter et al.,
2000; Casey et al., 2000; MacDonald et al., 2000; Ullsperger and
von Cramon, 2001). Varying levels of behavioral interference
effects across individuals have been shown to be directly positively
correlated with ACC activation (Botvinick et al., 1999; Carter et
al., 2000; Casey et al., 2000), making it possible to employ
conflict-related ACC activity as a marker of the level of conflict
experienced by the individual subject (Richeson et al., 2003).
Support for the view that the LFC implements cognitive
control stems from research showing increased left LFC
activation in anticipation of cued high conflict, but not low
conflict Stroop trials (MacDonald et al., 2000). MacDonald and
colleagues manipulated the expectation of conflict (and by
inference the strategic allocation of cognitive control) by switch-
ing between cued word-naming (low conflict) and color-naming
(high conflict) Stroop trials, and demonstrated a dissociation
between preparatory LFC activation and trial-conflict-related
ACC activation. In another recent fMRI Stroop study, left LFC
activation has been shown to be inversely related to levels of
response conflict, correlating positively with reduced interference
effects following high conflict trials (Egner and Hirsch, 2005), as
would be expected from brain regions underpinning cognitive
control (Botvinick et al., 2001).
We employed event-related fMRI in order to assess conflict-
and control-related activity in the ACC and LFC at varying levels
of response conflict in a Stroop paradigm in participants of high
and low hypnotic susceptibility, before and following hypnotic
induction (not containing specific Stroop-related instructions).
Participants performed a variant of the Stroop task that consisted
of four trial types of varying response conflict: word-naming of
congruent stimuli (low conflict), word-naming of incongruent
stimuli and color-naming of congruent stimuli (moderate conflict),
and color-naming of incongruent stimuli (high conflict). Note that
congruent trials incur neural conflict (e.g., Bench et al., 1993;
Carter et al., 1995) due to simultaneous activation in pathways that
compete for response selection, even though the final correct
response would be identical. This conflict is expected to be greater
in color-naming trials for the same reason that incongruent trials
cause greater conflict in color- than in word-naming, namely, the
more ballistic nature of the word-naming process. We expected
that, across groups and conditions, ACC activity would vary as a
function of response conflict, and that cognitive-control-related
LFC regions would be more activated in color-naming than in
word-naming trials (see MacDonald et al., 2000). Between groups
and conditions, however, the focused attention and the impaired
attention models of hypnosis make opposing predictions: The
focused attention model predicts superior efficiency of executive
attention (i.e., less conflict-related ACC activation) in highly
susceptible subjects both at baseline and after hypnotic induction,
relative to subjects with low susceptibility. The impaired attention
model, on the other hand, predicts superior efficiency in highly
susceptible subjects at baseline, but decreased attentional effi-
ciency (i.e., more conflict-related ACC activation) after hypnotic
induction, relative to subjects with low susceptibility. Additionally,
we explored how the predicted effect of hypnosis on conflict-
related ACC activity could be related to control-related processing
in the LFC, and/or changes in functional connectivity between
medial and lateral frontal cortical sites. To assess functional
connectivity between ACC and LFC at a high temporal resolution,
we measured EEG coherence between frontal midline and lateral
scalp electrodes in the same participants as in the fMRI study,
performing the same experimental paradigm.
Twenty-two healthy right-handed participants (mean age =
26.5, SD = 5.6; ten females), eleven of low and eleven of high
hypnotic susceptibility, gave informed consent to take part in this
T. Egner et al. / NeuroImage 27 (2005) 969–978
study, which received ethical approval by the Riverside Research
Ethics Committee, West London (ref. RREC 3193). Participants
were derived from a pool of pre-tested subjects, on the basis of
their hypnotic susceptibility. Hypnotic susceptibility was deter-
mined through pre-screening in group hypnosis sessions with the
Harvard Group Scale of Hypnotic Susceptibility, Form A
(HGSHS-A) (Shor and Orne, 1962), followed by an individual
hypnotic induction with the Stanford Hypnotic Susceptibility Scale
Form C (SHSS-C) (Weitzenhoffer and Hilgard, 1962). Participants
were classed as having low susceptibility if both their Harvard and
SHSS-C scores were ?3 (group mean score = 1.7), and as having
high susceptibility if both their Harvard and SHSS-C scores were
?9 (group mean score = 9.8). Baseline versus post-hypnosis self-
report ratings on 10-point Likert-scales of level of hypnosis in this
study disclosed a highly significant hypnosis ? susceptibility
interaction (P < 0.001), due to increased reported hypnotic depth in
the highly susceptible participants only (P < 0.001).
Stroop task and procedure
This variant of the Stroop paradigm was created and presented
using Presentation software (Neurobehavioral Systems, http://
www.nbs.neuro-bs.com). The task consisted of two word stimuli
(‘‘red’’ and ‘‘green’’, font size 32, Times New Roman) presented
in either red or green hue for 1500 ms centrally on a black
background, with a stimulus-onset interval of 10480 ms (4 TRs).
This represents a ‘‘slow’’ event-related design, approximately
replicating the event-timing employed in MacDonald et al.
(2000). Stimuli were presented in two runs of eight alternating
blocks of word-naming versus color-naming instructions, with six
congruent and incongruent stimuli presented in random order in
each block. Subjects were instructed to respond as quickly and
accurately as possible to each stimulus by pushing either the left
(for ‘‘red’’) or right (for ‘‘green’’) button on an MRI-compatible
response device, with their left or right index finger, respectively.
The task was run once at baseline, and once following hypnosis,
with order of hypnotic condition counterbalanced across partic-
ipants and groups. In the MRI scanner, stimuli were presented via
a projector to a mirror screen located at the head of the bore,
which the participants could view via a mirror attached to the
head coil. In the EEG laboratory, stimulus delivery was
implemented via a 17-in. screen positioned approximately 1 m
away from the participants.
Hypnosis induction and Stroop task instructions were admin-
istered via headphones from an audiotape after the subject was
comfortably placed in the bore of the scanner (or after the EEG
electrode cap preparation). These instructions were recorded in
the voice of the experimenter by whom subjects had been
individually screened (and who dealt with subjects at each
subsequent testing session). The hypnotic induction was specifi-
cally tailored to the needs of fMRI testing and utilized
suggestions which incorporated and reframed potentially uncom-
fortable aspects of the scanner environment in a non-threatening
manner. The induction made no reference to suggestions of
relaxation, heaviness, or sleep. Identical instructions were played
in both fMRI and EEG testing sessions, except for the exclusion
of scanner-specific references in the EEG session. A transcript of
taped instructions is available upon request.
fMRI data acquisition
Images were acquired employing a standard head coil with a
Siemens Vision 1.5-T scanner (Erlangen, Germany) at Charing
Cross Hospital, London. Functional images were recorded axially
along the AC–PC plane with a T2*-weighted gradient-echo
echoplanar imaging (EPI) sequence (echo time TE = 60 ms,
acquisition time TA= 2400 ms, repetition time TR = 2620 ms, flip-
angle 90-, in-plane resolution 3.5 mm ? 3.5 mm) affording whole
brain coverage with 25 contiguous slices of 5 mm thickness. For
each run of the Stroop task, there were 229 image acquisitions,
with the first 5 scans being discarded to allow the scanner to reach
steady state magnetic saturation. T1*-weighted structural images
were acquired with an MP-RAGE sequence (TE = 4 ms, TI = 300
ms, in-plane resolution 1 mm ? 1 mm, effective slice thickness = 2
mm, 128 slices).
fMRI data analysis
Functional MRI data were analyzed using SPM2 software
(Wellcome Department of Cognitive Neurology, London, UK; see
http://www.fil.ion.ucl.ac.uk/spm). EPI volumes were corrected for
differences in acquisition slice-timing, spatially realigned to the
first volume of the first session, and a mean EPI image was
calculated to which the structural image was co-registered. Trans-
formation parameters were derived from normalizing the co-
registered structural image to a template brain within the stereo-
tactic space of the Montreal Neurological Institute (MNI), and the
derived parameters were then applied to the EPI volumes.
Normalized images were smoothed with a Gaussian kernel of
7 ? 7 ? 10 mm full-width at half-maximum (twice the size of the
original voxel dimensions). Functional data were analyzed using a
general linear model (GLM) approach (Friston et al., 1995).
Regressors of event-related BOLD responses were modeled in each
subject for correct responses from each trial type (word-congruent,
word-incongruent, color-congruent, color-incongruent) using a
standard hemodynamic response function (canonical HRF), and
were used as covariates in GLM analyses for each subject in order
to generate voxel-based statistical parametric maps (SPM). Error
trials were modeled as a separate regressor. To remove low-
frequency temporal confounds, data were high-pass filtered
(128 s), and an autoregressive function (AR-1 in SPM2) was
employed to estimate for temporal autocorrelation in the data and
correct the degrees of freedom accordingly. Contrast SPMs were
calculated for each subject individually and these contrasts were
then employed for random effects analyses at the group level.
A priori analyses of conflict-related ACC activation were
carried out in the following way: First, event-related activations
to moderate and high conflict stimuli were assessed across
groups and conditions within the ACC, as defined by an
anatomical ROI mask consisting of Brodmann areas BA 24 and
BA 32, applied with the WFU Pick Atlas (see http://
www.rad.wfubmc.edu/fmri) (Maldjian et al., 2003). Activation
foci within the ACC that significantly activated above a false
discovery rate (FDR) (Genovese et al., 2002) threshold of 5%
(i.e., P ? 0.05, corrected) and a cluster-extent threshold of a
minimum of 10 contiguous voxels to both moderate and high
conflict stimuli were then employed as a functional ROI,
created with Marsbar software (Brett et al., 2002; http://
marsbar.sourceforge.net/). From this functionally defined ROI,
mean conflict-related activation data were extracted for each
T. Egner et al. / NeuroImage 27 (2005) 969–978
subject and entered into a 2 ? 2 condition (baseline vs.
hypnosis) by group (low vs. high susceptibility) analysis of
variance (ANOVA). Subsequently, we employed the same
analysis strategy to assess activation in putative cognitive
control regions of the LFC, namely, by defining functional
ROIs exhibiting more activation on color-naming than on word-
naming trials within an anatomical ROI comprising BAs 8, 9,
10, and 44–46.
EEG acquisition and analysis
EEG was recorded in the Cognitive Neuroscience laboratory,
Imperial College London, Charing Cross campus on a Neuroscan
Synamps system (Compumedics Inc.) in an electrically shielded
chamber via a 28-channel Electro-cap (ECI International). Signal
was acquired and digitized at a sampling rate of 500 Hz and passed
through a 0- to 100-Hz bandpass filter (24 dB/octave roll-off).
Electrodes were placed in accordance with the international 10–20
system, with a ground electrode placed 1.5 cm anterior to the
central frontal electrode (FZ), and referenced off-line to linked
earlobe electrodes. All electrode impedances were kept below 10
kV. The electrooculogram (EOG) was recorded with tin cup
electrodes placed on the orbis occularis muscle above and below
the left eye, and on the left and right outer canthi, approximately 1
cm lateral to either eye. Eye-blinks, horizontal, and vertical eye-
movements were removed by applying an offline artifact correction
algorithm (Croft and Barry, 2000). All data processing and
analyses were carried out with Neuroscan software (version 4.2).
EOG-corrected data were epoched into 1024-ms intervals around
each stimulus presentation (?100 ms–924 ms) and baseline-
corrected with respect to a 100-ms pre-stimulus interval. Epochs
containing amplitude fluctuations exceeding T100AV were rejected
as artifact-contaminated. The EEG epochs were grouped according
to the four trial categories (word-congruent, word-incongruent,
color-congruent, color-incongruent) for the wakeful and hypnotic
task conditions separately, excluding error trials. Average coher-
ence values were then calculated for delta (0–3.9 Hz), theta (4–7.9
Hz), alpha (8–12.9 Hz), beta (13–29.9 Hz), and gamma (30–49.9
Hz) frequency bands and used in the statistical analyses (see
Results). The EEG recordings were carried out approximately 2 to
4 weeks after the fMRI recordings.
fMRI behavioral data
Subjects exhibiting outlier values (>2 SD from the mean) were
excluded from the behavioral data analyses, and error trials were
excluded from RT analyses. Significant Stroop interference effects
Fig. 1. Stroop performance and ACC BOLD responses at varying levels of response conflict. (A) Mean reaction times (TSEM) for the different Stroop trial
types. (B) Mean accuracy rates (TSEM) for the different Stroop trial types. (C) Significant activations to moderate response conflict (top panel: incongruent
word-naming/congruent color-naming > congruent word-naming) and the high conflict contrast (bottom panel: incongruent color-naming > congruent word-
naming) in the (right) ACC. Activity is displayed at a false discovery rate (FDR) of P = 0.05 with an extent threshold of at least ten contiguous voxels. For
display purposes, activations are superimposed on a partially inflated right hemisphere medial wall of a normalized single subject T1 scan (segmentation and
inflation was carried out with Brain VISA software; http://brainvisa.info/index.html).
T. Egner et al. / NeuroImage 27 (2005) 969–978
were observed in the RT data (Fig. 1A) for both congruency
(F[1,18] = 18.25; P < 0.001) and type of instruction (F[1,18] =
7.02; P < 0.05). In line with expectations, RTs to high conflict
trials were largest, significantly larger than in moderate conflict
trials (t = 3.64; P < 0.005; t = 1.75; P = 0.097) and in low
conflict trials (t = 5.64; P < 0.001). Compared to the low
conflict trials, RTs were significantly larger in both moderate
conflict conditions (t = 4.44; P < 0.001; t = 2.59; P <
0.05), with no difference in RTs between moderate conflict trials.
The accuracy data mirrored the interference effects of the RT
results (Fig. 1B), main effects being detected for congruency
(F[1,18] = 24.84; P < 0.001), and instruction (F[1,18] = 10.89;
P = 0.005). As expected, high conflict trials produced most errors,
significantly more than the moderate conflict (t = 2.83; P <
0.05; t = 3.59; P < 0.005), and low conflict trials (t = 4.55;
P < 0.001). Both moderate conflict trial types induced significantly
higher error rates than the low conflict condition (t = 2.75; P <
0.05; t = 3.22; P = 0.005), with no difference in accuracy
between the moderate conflict conditions. There were no effects
involving hypnotic induction or susceptibility variables.
fMRI imaging data
In order to verify that ACC activation was susceptible to the
manipulation of conflict levels in the current study, blood
oxygenation level-dependent (BOLD) responses to different levels
of response conflict were assessed within the ACC by comparing
event-related activation in moderate versus low conflict trials
(moderate conflict contrast), and in high versus low conflict trials
(high conflict contrast), excluding error trials. As hypothesized, the
extent of ACC activation increased with conflict level across
groups and conditions, as can be seen in Fig. 1C (see Table 1 for
summary of activations). ACC regions that were susceptible to
both moderate and high conflict contrasts served as a functional
ROI for comparing activations between groups and conditions (see
Fig. 2A and Table 1). A 2 ? 2 condition (baseline vs. hypnosis) by
group (low vs. high susceptibility) ANOVA on conflict-related
activation revealed a significant condition ? group crossover
interaction effect (F[1,20] = 6.27; P < 0.05), as shown in Fig. 2B.
This interaction effect was characterized by significantly higher
ACC activation in highly susceptible subjects compared to subjects
with low susceptibility in the hypnotic condition (t = 2.25; P <
0.05), but not at baseline (t = 1.58; P = 0.13). Furthermore,
conflict-related ACC activation in the highly susceptible subjects
showed a significant increase from baseline to hypnosis (t =
2.67; P < 0.05), whereas there was a non-significant decrease in
the subjects with low susceptibility (t = 1.10; P = 0.29). In
order to corroborate these results in the more traditional framework
of comparing incongruent to congruent trials, these trials were
contrasted irrespective of color- or word-naming instructions. This
contrast identified a conflict-related activation cluster (26 voxels)
in the right medial frontal gyrus (BA 32; x = 6, y = 8, z = 44). This
cluster showed the same pattern of condition ? group interaction
as the previous conflict-responsive ROIs (F[1,20] = 5.10; P <
0.05), characterized by a significant increase in activity from
baseline to hypnosis in the highly susceptible subjects only (t =
2.37; P < 0.05).
LFC regions of cognitive control were identified by contrast-
ing color-naming with word-naming trials across groups and
conditions. Within bilateral LFC, no region displayed significant
activation for this contrast at an FDR of P < 0.05. However,
when adjusting the statistical threshold to an uncorrected
voxelwise level of P < 0.001, a single significant activation
cluster (27 voxels) was obtained in the left LFC (see Fig. 3A),
namely, in the left inferior frontal gyrus (GFi) in BA45 (x = ?56,
y = 14, z = 5). A 2 ? 2 condition (baseline vs. hypnosis) by
group (low vs. high susceptibility) ANOVA on control-related
activity in this ROI revealed no main or interaction effects (Fig.
3B), indicating that there were no differences in the allocation of
cognitive control resources between groups and conditions.
Finally, an exploratory analysis of condition by group effects
across the whole brain as well as regions of interest (bilateral
Anterior cingulate foci activated by moderate response conflict, high response conflict, or both
Talairach Talairach coordinatesCluster sizeVoxelwise P
Moderate conflict CG
High conflict4 40
Note. BA = Brodmann Area; Talairach labels: CG = Cingulate Gyrus, AC = Anterior Cingulate.
T. Egner et al. / NeuroImage 27 (2005) 969–978
prefrontal and parietal cortices) did not yield any significant
effects after correction for multiple comparisons. When lowering
the statistical threshold to uncorrected voxelwise P < 0.001, a
single cluster (18 voxels) was found in the left parahippocampal
gyrus (BA 28; x = ?20, y = ?20, z = ?22), where highly
susceptible subjects displayed a hypnosis-specific increase in
activation, compared to subjects with low susceptibility. In
summary, in accordance with the impaired attention model
hypotheses, highly susceptible participants were characterized
by a significantly decreased efficiency of conflict resolution in the
hypnotic condition, relative to baseline as well as with respect to
participants with low susceptibility. The significant increase in
conflict-related ACC activity in highly susceptible subjects in the
hypnosis condition was not accompanied by a commensurate
increase in cognitive-control-related LFC activation.
EEG behavioral data
Subjects exhibiting outlier values (>2 SD from the mean) were
excluded from the behavioral data analyses, and error trials were
excluded from RT analyses. Stroop reaction time data revealed the
familiar main effects of stimulus congruency (F[1,18] = 37.5; P <
0.001) and instruction (F[1,18] = 12.0; P < 0.005). High conflict
trials were associated with slower reaction times than moderate
conflict trials (t = 6.58; P < 0.001; t = 3.26; P < 0.005),
and low conflict trials (t = 8.70; P < 0.001). The two moderate
conflict conditions did not differ from each other, but both induced
significantly slower responses than the low conflict trials (t =
4.22; P < 0.001; t = 2.9; P < 0.01). No hypnosis or hypnotic
susceptibility effects were obtained. Response accuracy again was
affected by stimulus congruency (F[1,18] = 16.35; P < 0.005) and
instruction (F[1,18] = 5.44; P < 0.05). High conflict trials
displayed the lowest accuracy rate, inducing significantly more
errors than moderate conflict trials (t = 2.86; P < 0.05; t =
1.93; P = 0.069), and low conflict trials (t = 3.51; P < 0.005).
Furthermore, moderate conflict trials induced higher error rates
than low conflict trials (t = 4.20; P < 0.001; t = 2.57; P <
0.05). However, these accuracy data were qualified by a
hypnosis ? susceptibility interaction (F[1,18] = 4.79; P < 0.05),
as participants with low susceptibility improved their accuracy in
the hypnotic condition (t = 2.60; P < 0.05), while highly
susceptible participants did not (see Fig. 4A).
EEG coherence data
Functional connectivity (EEG coherence) between neural
processes in frontal midline (Fz electrode) and left dorsolateral
frontal sites (F3 electrode) was calculated for delta, theta, alpha,
beta, and gamma frequency bands (see Methods), and employed
Fig. 3. Cognitive-control-related area in left LFC and its response
magnitudes in subjects of low and high hypnotic susceptibility, at baseline
and following hypnosis. (A) LFC ROI displaying significantly higher
activation (uncorrected P < 0.001) to color-naming than to word-naming
trials, superimposed on a partially inflated left hemisphere of a normalized
single subject T1 scan (segmentation and inflation was carried out with
Brain VISA software; http://brainvisa.info/index.html). (B) Mean control-
related LFC ROI activity (beta weights T SEM) for baseline and hypnotic
conditions, in participants with low and high hypnotic susceptibility.
Fig. 2. Conflict-susceptible regions of the ACC and their response
magnitudes in subjects of low and high hypnotic susceptibility, at baseline
and following hypnosis. (A) ACC ROIs displaying significant activation
(FDR < 0.05) to both moderate and high response conflict, superimposed
on a partially inflated right hemisphere medial wall of a normalized single
subject T1 scan (segmentation and inflation was carried out with Brain
VISA software; http://brainvisa.info/index.html). (B) Mean conflict-related
ACC activity (beta weights T SEM) from the ROIs in panel A for baseline
and hypnotic conditions, in participants with low and high hypnotic
T. Egner et al. / NeuroImage 27 (2005) 969–978
in 2 ? 2 ? 5 condition by group by frequency band ANOVAs.
While there were no effects on coherence for low conflict, or
moderate conflict conditions, in the high conflict condition, a
hypnosis ? band ? susceptibility interaction effect was evident
(F[4,15] = 2.51; P < 0.05). Inspection of the data revealed that
the interaction stemmed from the fact that gamma band coherence
decreased in highly susceptible subjects, but increased in subjects
with low susceptibility between baseline and hypnotic states (see
Fig. 4B). In order to confirm that these results were specific to
midline–left frontal connectivity, the same analyses were carried
out for the right frontal lateral site (F4 electrode). There were no
significant results obtained from this analysis. In summary, the
EEG coherence analyses have supported the suggestion of a
decreased functional connectivity between frontal midline and left
frontal regions in highly susceptible subjects after hypnotic
Investigating executive attention processes in relation to
hypnosis and hypnotic susceptibility, we employed a Stroop
paradigm that successfully produced interference effects on
reaction time and accuracy rates, resulting in significantly different
levels of low, moderate, and high response conflict, replicated
across fMRI and EEG recording sessions. In lieu of these
behavioral effects, we demonstrated that frontal midline activation
of the dorsal anterior cingulate cortex covaried positively with the
level of response conflict, confirming results from previous studies
(Botvinick et al., 1999; Carter et al., 2000; Casey et al., 2000).
Importantly, the identification of conflict-responsive ACC loci
allowed us to compare neural efficiency in conflict resolution at
baseline and following hypnosis, between groups of subjects with
low or high hypnotic susceptibility. Conflict-related ACC activa-
tion displayed an interaction effect (see Fig. 2), as this activation
increased significantly from baseline to hypnosis in the highly
susceptible subjects only, leading to significantly more conflict-
related ACC activation in highly susceptible subjects than in
subjects with low susceptibility after hypnotic induction. These
data were obtained under conditions of equal performance levels
between the experimental groups, and can therefore not be
accounted for by differential task difficulty. This lack of behavioral
effects can likely be attributed to the much longer inter-stimulus
intervals employed in the current experiment in comparison to
previous studies that have documented such effects (e.g., Jamieson
and Sheehan, 2004; Kaiser et al., 1997; see also Nordby et al.,
1999). These results are directly supportive of both the proposition
that differences in executive attention processes mediate the stable
trait variable of hypnotic susceptibility, and that executive function
is impaired in highly susceptible individuals following hypnosis
(Crawford and Gruzelier, 1992; Gruzelier, 1990, 1998, 2004;
Hilgard, 1965, 1977; Jamieson and Sheehan, 2004; Woody and
Bowers, 1994). The results do not support the notion that hypnosis
in highly susceptible subjects represents a state of highly focused
attention (Barber, 1960; Spiegel, 2003; Tellegen and Atkinson,
But what exactly happened to the highly susceptible partic-
ipants, at the neural level? Control-related activation in the inferior
frontal gyrus of the left LFC did not distinguish between baseline
and hypnotic conditions or low and high hypnotic susceptibility
(see Fig. 3). Thus, it appears that the increased conflict-related
ACC activation in highly susceptible subjects in the hypnosis
condition was not accompanied by a concurrent strategic increment
in cognitive control, as would be expected under normal circum-
stances (Botvinick et al., 2001, 2004; Kerns et al., 2004). These
fMRI data suggest the possibility of a decoupling of conflict-
monitoring and cognitive control function in highly susceptible
subjects after hypnotic induction, corresponding to a breakdown in
the functional integration of two key components of the frontal
attentional control system. It should be noted that the control-
related focus identified in the present study was located more
caudal and inferior to regions reported in previous studies that
explicitly dissociated control-related from conflict-related activity
(Egner and Hirsch, 2005; MacDonald et al., 2000). The current
control-related activation is likely to be reflective of sustained
implementation of task-specific processing requirements, as
compared to adaptation to changes in conflict on a trial-by-trial
basis (Egner and Hirsch, 2005; MacDonald et al., 2000). Its locus
in the GFi indeed corresponds very closely to previous studies that
have interpreted this region as imposing an attentional set geared at
selecting task-relevant information at a conceptual/semantic level
rather than the response-level (Brass and von Cramon, 2004;
Milham et al., 2001; Zysset et al., 2001). Similarly, this left inferior
frontal region has been conceptualized as underlying the top–
down modulation of contention scheduling (Shallice, 2002) and
contextual control processes (Koechlin et al., 2003), such as
associating external cues with the appropriate choice of action
(Passingham et al., 2000).
Fig. 4. Stroop accuracy data and EEG gamma band coherences. (A) Performance accuracy (TSEM) on the Stroop task for low and high susceptible hypnotic
subjects, at baseline and in hypnosis. (B) Mid- to left frontal EEG gamma band coherence values following high conflict trials, in low and high susceptible
hypnotic participants, at baseline and in hypnosis.
T. Egner et al. / NeuroImage 27 (2005) 969–978
In support of the notion of a decoupling between conflict
monitoring and control processes in hypnosis, the results obtained
from analyzing functional connectivity, by means of EEG
coherence measures, show that low and high susceptibility groups
were distinguished by baseline-to-hypnosis changes in gamma
band coherence between frontal midline and left lateral scalp sites.
In participants with low susceptibility, gamma band coherence
showed an increase, whereas in highly susceptible participants, it
was found to be decreased, and this pattern was mirrored in the
behavioral accuracy data (see Fig. 4), recalling previous findings of
occasional performance improvement in subjects with low
susceptibility following hypnotic induction (see Gruzelier, 1998,
2000; Gruzelier et al., 2002). Coherence in the gamma frequency
range has frequently been associated with functional connectivity
processes, such as the binding of various features of a stimulus in
primary sensory cortices (Tallon-Baudry and Bertrand, 1999) or of
different stimulus classes paired during associative learning tasks
(Miltner et al., 1999). Furthermore, it has been previously reported
that hypnosis interfered with a (non-hypnotic) relationship between
subjective ratings of pain and the amplitude of gamma oscillations
localized to the ACC with low-resolution tomography (LORETA)
(Croft et al., 2002).
Thus, together these data support the proposal that hypnosis in
highly susceptible individuals may be underpinned by a profound
alteration of frontal lobe functions (Gruzelier, 1998, 2000). We
note that this was specific to regions engaged by the cognitive
challenges posed by the Stroop task, and no background
accompaniment of hypnosis was detected elsewhere in the brain.
More specifically we found a fractionation between ACC conflict
monitoring and left LFC cognitive control processes (Jamieson and
Sheehan, 2004). This complements previous reports of altered
frontal EEG gamma coherence following hypnosis in highly
susceptible subjects (Jamieson et al., 2003). Interestingly, Kaiser
and colleagues (reported in Gruzelier, 1998) have also found that
EEG alpha coherence was altered during hypnosis specifically
within the left frontal lobe during a Stroop-like task. However, in
that experiment (Kaiser et al., 1997), a further dissociation between
ACC processes measured by error-related negativity (NE, conflict
monitoring) and error-related positivity (PE, context updating) was
disclosed in the more highly susceptible participants. The NE was
unaffected by hypnosis whereas hypnosis abolished the PE. This
was interpreted as hypnosis influencing the impact of motivational
factors and so compromising Stroop performance (Gruzelier, 1998;
Kaiser et al., 1997).
In conclusion, hypnotic susceptibility interacted with hypnotic
induction in the effects on conflict-related ACC activity during a
Stroop task. Following hypnosis, highly susceptible subjects
exhibited significantly increased conflict-related ACC activation,
indicative of decreased attentional efficiency, as compared to
baseline, and as compared to subjects with low hypnotic
susceptibility. This increased conflict, however, was not accom-
panied by corresponding adjustments in the allocation of cognitive
control. High conflict events in the hypnotic condition in highly
susceptible participants were furthermore characterized by a
relatively decreased functional connectivity between midline and
left lateral frontal lobe sites. These data are compatible with the
proposal that trait differences in response to hypnotic suggestions
(hypnotic susceptibility) are mediated by differences in attentional
processing, and that hypnosis in highly susceptible subjects is
underpinned by a functional decoupling of response conflict
monitoring and cognitive control processes. These results contra-
dict the assumption that hypnosis is directly associated with highly
focused attention in highly susceptible hypnotic subjects. However,
we suggest that the hypnosis-related decoupling of executive
functions is highly malleable, as in the presence of strategic
attentional instructions, superior conflict resolution can be
achieved by highly susceptible participants (Raz et al., 2002,
2003; Sheehan et al., 1988). The challenge of these results is now
to delineate the mechanism(s) underlying the fractionation of
executive functions, which may offer profound insights into
attentional processes in the normal and disordered brain. The
results contribute to a growing body of evidence from other
investigators implicating the ACC in the hypnotic process and
importantly in its analgesic actions (Crawford et al., 1998; De
Pascalis et al., 2001; Derbyshire et al., 2004; Faymonville et al.,
2000; Horton et al., 2004; Rainville et al., 1999; Ray et al., 2002;
Wik et al., 1999).
The authors would like to thank D. McRobbie, R. Quest, A.
Papadaki, and P. Nachev for technical support and advice. This
research was supported by a grant to John Gruzelier from the
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