gruzelier ch 1998 working model
TRANSCRIPT
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Contemporary
Hypnosis
(
998)
Vol. 15,No. ,
pp.3-21
A
WORKING
MODEL
OF
THE NEUROPHYSIOLOGY
OF
HYPNOSIS:
A REVIEW
OF
EVIDENCE
John Gruzelier
Imperial Collegeof Science,Technologyand Medicine,London, UK
Abstract
Neuropsychophysiologicalvidences reviewed estinga three-stage,op-down
work-
ing model of the traditional hypnotic
relaxation nduction nvolving:
1)
a thalamo-
cortical attentional network engaginga left frontolimbic focusedattention control
system nderpinning ensory ixation and concentration n the induction;
2)
instate-
ment of frontolimbic nhibitory systems hrough suggestions f tiredness
t fixation
and relaxation
whereby
anterior executive unctionsare
suspended nd directedby
the induction;
3)
engagement f right-sided emporoposteriorunctions
hrough
pas-
sive mageryand dreaming.A selectivity f action n high susceptibles asa hallmark
of the
studies. ncreased
Stroop
interferencecoincidedwith maintenanceof error
detectionand abolition of error evaluation
potentials,
nterpretedas dissociation
f
cognitive and affective executive systemsof the anterior cingulate.
Verbal, category
and design luency tasks were dissociatedwith hypnosiscentring on
left
anterior
processes
s seen n left lateral and
medial educedEEG connectivity. imbic modu-
lated electrodermal rienting
responses nd frontal modulatedmismatchnegativity
waveswere nhibited.
Asymmetries n electrodermal nd electrocorticalesponseso
tonesshifted o favour the right hemisphere, n asymmetry lsoseen n visual
sensi-
tivity. Haptic
processing
nd
visual sensitivitydisclosedmore distributedchanges
n
medium
susceptibles, hile low susceptibleswere characterized y
poorer
attentional
functionsat baseline
nd mprovementshrough he nduction.
Key words:EEG, ERPs,attention aterality, rontal
imbic
cingulate
Introduction
This article
provides
a review of experiments, hematically ather than chronologi-
cally structured, hat
were carried out in the
Charing
Cross aboratory of Cognitive
Neurosciencewith the aim of understandinghe neuropsychophysiologicalasis
of
hypnosis.Hypnosis
was
defined operationallyon the basis
of the traditional relax-
ation
procedure,
which beganwith eye ixation,suggestionsf
relaxationand eyeclo-
sure,and was ollowedby imageryassociated ith deep elaxationand a dream.
This
was applied n all experiments xceptone where the active-alert
rocedure B6nyai
and
Hilgard,I976) wascompared.During the induction here were behavioural hal-
lenges o assess epth of hypnosis, nd at the endquestionsabout memory for the
induction,a
post
hypnoticsuggestion nd
subjective atings.The
purpose
was o
unravel
someof the changesn brain
activity
hat accompanyhe hypnotic nduction
in both high and ow susceptiblendividuals, nd
eatures
hat
may differentiate hem
in the baseline tate.
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4 Gruzelier
The
history of localizing neurophysiological
mechanismsn hypnosisbegan by
likening
hypnosis o sleep.Pavlovdemonstrated
he existence f hypnosis n
his
con-
ditioned eflex
studies n dogsand attributed his to a
partial
and spreadingnhibition
of the cortex,
essextensive han occurs n sleep,
hough Heidenhainhad reasoned
earlier hat
more than the cortex was nvolvedbecause
nimalsdid not behaveas
f
they
were decorticate
Windholz,
1996).
Although sleepbecamean ncreasingly
op-
ular analogy,
o dateelectroencephalographic
EEG)
studies avenot found
similari
ties betweenhypnosis nd sleep
for
a review seeCrawford and Gruzelier,1992).
At
the same ime sleepcanbe inducedby instructions f hypnosis, ut conventional ro-
cedures topshort
of sleep nduction.Hernandez-Peon
1977)
proposed
hat hypnosis
wascloser o wakefulnesshan sleep,
nvolvingalterations n both consciousness
nd
executive unctions,
which he local ized o the
midbrain,
pons
and medul la.
Nevertheless, epending
n the natureof the
induction,dream-like eaturesare
close
to the hypnoticexperience
f many high susceptibles.
Recordings
rom intracranialelectrodes
n
epileptic
patients
have disclosed
he
importanceof l imbic structures
n hypnosis.Craiselneck,
McCranie and Jenkins
(1956)
eported
anecdotallyhat hypnosiswas erminated
each ime the hippocampus
was electrically timulated.
De Benedittisand Sironi
(1986)
demonstrated
n a high
hypnotizable that
there was a reduction in interictal
focal abnormalities n
the hip-
pocampus
uring
hypnosis nd an increasen alpha
activity. n a second
atient
hey
concluded hat hypnosiswas associated ith functional nhibition of the amygdala,
because timulation
of the amygdala roused
he
patient
rom hypnosis
nlike stimu-
lation of the adjacentand
reciprocally onnected
ippocampus. lectricalactivity
n
the
amygdalabecamesynchronized
with hypnosis
whereasactivity in the
hippocam-
pus
became esynchronized
De
Benedittisand Sironi,
1988).
In the 1960s
arallels
were drawn between
hypnosisand right
hemispheric
ro-
cessingand
high hypnotic susceptibles
ere assumed o be characterized
y right
hemisphericity.
his
point
of view has been
popularized
and has
been found to be
important
n the clinicaluse
of hypnosis
Pedersen,
984).Aside from evidence
rom
cognitivestudies
with
putative
hemisphere
pecific asks, here
were also neuropsy-
chophysiological
measures
which took into accountbrain
anatomy such as
EEG,
dichotic
listening and conjugate
ateral eye movements
Crawford
and Gruzelier,
1,992). xperimental evidence
was, however,conflictual,
but the methodologies
f
many studieswere
questionable
Gruzelier,
1988).
Methods of inducing
hypnosis
were
various and often
poorly
described.Often there
was a failure to distinguish
between
high and
low
susceptibles
r to attribute
changes n low susceptibles
hat
were absent
n high susceptibles
o the hypnotic
process.
eldom
was evidence
ited
of test-retest
eliability,or of
replication,or of validationof
hypnotic evel during
he
experimental
rocedure.
In integrating he
resultsof a decadeago a three-stage
orking model
of the
induction
process
was
proposed
Gruzelier,
1988,
990).
Stage
: The initial instructions
of fixating on a
small object and listening
o the
hypnostist's
oicewas
posited
o
involve an attentional
network ncluding halam-
ocortical
systems nd
parietofrontal
connections
with engagement
f a left ante-
rior focusedattention control system.This underpins he focused,selective
attention
nherent n fixation and istening
o the hypnotist's
oice,
processes
hat
together
require left hemispheric
rontotemporal
processing.
Stage
I: The first stage
s then replacedby eye closure,
uggestions
f fatigue at
continued
ixation, and tiredness ogether
with deep relaxation.
This sets
n
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Neurophysiology
of hypnosis 5
motion
frontolimbic nhibitory
processes
nderpinning
he suspension f
reality
testing and critical evaluation,
and the handing over
of executiveand
planning
functions o the
hypnotist; he
letting
go'
component
f the hypnotic
nduction.
.
Stage
II: The third stage nvolves
nstructions f relaxed,
passive
magery eading
to a
redistributionof functionalactivity and
an augmentation f
posterior
cortical
activity,
particularly
of the
right hemispheren high susceptibles. implifying
he
verbal contentof the
inductionmessagemay also
acilitate ight hemispheric
ro-
cessing, s
does emphasizing
ast
experience
nd emotion.
n
contrast,
ow sus-
ceptibles
ail to show engagement
f left frontal attentional
control mechanisms,
or if there is focal attentional engagement,ow susceptiblesail to undergo he
inhibitory,
etting
go process.
his
working model wil l serve o
structure he
review of findings.
Here emphasis ill be
placed
on the cognitive
neuroscience f
hypnosis;
mplications or socio-cognitive pproaches
ill be
found n
a
commen-
tary
(Gruzelier,
1998)on a theoretical
aper
by Wagstaff
1998).
Thalamo-frontal-limbic
attentional
processes
Electrodermal
o rienting, habituation,
sensitizationand tonic
reactivity
We
first investigated he basic attentional
processes
f orienting,
which
represents
focusing f attention,
and of
habituationwith stimulus epetition,
which allowsatten-
tion to be
redirected, nd which
nvolvemodulationby the
limbic system,n
particu-
lar the amygdala ndhippocampuse.g.PribramandMcGuinness, 975;Gray,1982).
The electrodermal
esponse aschosen
ecause mong
physiological
measures
t has
the advantage
of
indexing sympatheticnervous
systemactivity unconfounded
by
competing
parasympatheticnfluences.Using a standardize d
one orienting and
habituation
paradigm
Gruzelier
and
Venables,1972)he effects
of hypnosis n
ori-
enting
responseso tones hat
were interspersedwith the
hypnotic nduction
were
monitored n normaland
patient
volunteers
Gruzelier
and Brow, 1985).Subjects
ook
part in
three
sessions eparated
y four weeks o avoid
carryovereffectson
habitua-
tion.
They were first
monitored o
provide
a baseline
measure nd to equate
groups
for
individual differences
n rate of habituation.
Then with sessionorder
counterbal-
anced
hey experienced
hypnosissession nd one
of two control
conditions.
The
control
conditions onsisted
f either a story read by
the hypnotist,or
relaxing isten-
ing to a story or a periodequivalentn length o the hypnotic nductionprior to the
introduction of
the tones,which
were
presented
without any accompanying
erbal
message. ypnoticsusceptibility
asmonitored
hroughout he experimental
ession.
The
outcome
was clear and
dependedon
level of suscep tibility.
s shown n
Figure 1, n the
group
distributions
of orientingand
rate of habituation
he hypnosis
conditionwas distinguished
rom the three
control conditions
hrough a higher
nci-
denceof both
non-responding nd
non-habituation, bimodal
distribution.
t
was
he
high susceptibles
ho showeda
reduction n orientingand/or
asterhabituation
with
hypnosis,
hereasow susceptibles
howed etarded
habituationwith hypnosis,
scan
be seen
n Figure2.
Comparisons
with other
featuresof electrodermal
activity shed
ight on arousal
and
attentional
processes.
n hypnosis
or
the
group
as a whole there
was an absence
of
sensitizationo a
test one
presented
owards
he end of the session
hile through-
out
the induction here
wasan increase
n
electrodermal
on-specific
esponses.
t is
important o
note
that
both theseeffects
were sharedwith the control
story condition
and did
not vary with
hypnotic
susceptibility.
rom this
t canbe infered hat
listening
to the story
and to the
hypnotic nduction
produced
a
similar degreeof autonomic
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Gruz.elier
t2
10
TRIALS
MIL
HABITUATION
STUDENIS
ND
PATIEMS
TONES
LONE
IONES
ALONE
AFITRSTORY
ffi
Patients
l--1
Students
HYPNOSIS
ITH ONES
AFTER
NDUCTION
TONES
WITH
STORY
R
2
e
L
0
Figure 1. Electrodermalorienting
response abituation
relaxation fter
istenins o a storv.andstorvconditions.
8 t 2 1 6
baseline
(tones
alone),
hypnosis,
Patients
Students
Increase
n
Habituation
Same abituation
Decrease
n
Habituation
0 2 t 4 6 8 1 0
Susceptibilty
Score
Figure
2.
Subjects
ategorized ccording
o increase, ecrease r
no changen
habituation rom
baseline
o hypnosis sa
function
of
inductionsusceptibility core.
arousability
and attentional engagement
and these did
not vary with susceptibility.
Turning
to the relaxation condition,
this was insufficient
to change either
habituation
(see
also
Teasdale, 1972) or sensitization,
so that the
facilitation of habituation
could
not be explained
away as a function of
relaxation. At the same
time some compo-
nents of arousal
reduction were associated
with hypnosis.
This was shown by
fewer
4
in
q ?
i 3 -
a
'E-
0
o 9
L
o o
O L
2 o
4 8
4
8
12
16
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Neurophysiology
of hypnosis 7
non-specific esponses
uring
hypnosis
both in the first half and secondhalf
of the
hypnotic nduction
as
well
as by reductions n
tonic levels of skin conductan ce.
However, one high susceptible ad levels
of skin conductancewo standard
devia-
tions above he control
group
mean,
ndicating hat a reduction n tonic arousal s not
a necessary
art
of the hypnotic
process
s
will
be confirmed ater in an experiment
with the active-alertnduction
procedure.
The facilitation of habituation with
hypnosiswas replicated n an experiment
designed o comparehypnosiswith simulatinghypnosls n
medium/highhypnotiz-
ables Gruzelieret al., 1988).Subjectswere examined irst in a baseline ession nd
then assigned ith the Barber
Suggestibility cale
Barber,
1969) o the simulatoror
hypnosis
groups
matched
or suggestibi l i ty, lectrodermal eactivi ty
and sex.
Hypnotic susceptibility asmonitored
hroughout he second ession s n the former
experiment.Levels of susceptibilityall fell within the
moderate o high range. As
before, rate of habituation was faster with hypnosis
n the susceptible ubjects
whereas n
simulatorshabituationwas slower.
Simulators
were
more arousedduring
the nduction
prior
to
presentation
f the tones
p
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8 Gruzelier
magnitude
differencewave
at baselineand a
progressive
eduction
n MMN
with
each
stageof the
induction and n keeping
with frontal inhibition.
By the
later stage
of the
induction MMN
was negl igible n both
the lateral
frontal
placements.
Importantly
oppositechanges
were manifested
y the low
susceptible
roup.
Whereas
at baseline heir
differencewave
was absent, here
was a
progressive
increase
n MMN through
he experiment, ntil
in the last condition
he magnitude
of
the difference
wave
wason a
par
with the results
n high susceptibles
t baseline,
ug-
gesting
n ncreasing
nhancement
f attentional
processing.
HIGHSUSCEPTIBLES
l H 1
[f H2
LOW
SUSCEPTIBLES
tr--t R
I H 1
t--1 H)
Figure 3. Mismatch
negativityscores
n
baseline
B),
induction
(H1)
and extended
nduction
(H2)
in high and ow susceptible
roups.
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Neurophysiologyof hypnosis 9
Summary
There was a consistency etween he electrocorticalMMN
and
electrodermalmea-
sures
n
depicting opposite changes rom baseline o hypnosis n susceptibleand
unsusceptibleubjects. ongruent
opposing
ffectson attention
have
alsobeen
ound
in a recent Finnish study involving a computerizedvigilance task. High susceptibles
showedan ncreasen omissionerrorsand
greater
variability n RTs from baseline o
hypnosis,while low sus ceptibles howeda reduction n errors and RT variance
(Kallio
et
al., 1998).Together hesestudies
show
that whereas
susceptible
ubjects
evinced nhibitory influenceson attention with hypnosis, nsusceptible ubjects
improvedattentional
performance
s he nduction
progressed.
Anterior inhibitory
processes
Fr o nto
-
imb ic sup e v so ry attentio nal s
y
s em
We went on to examineevidence f frontal nhibition n the contextof contemporary
modelsof anterior functions hat focus on attentionalcontrol systems
Posner
and
Peterson,1990;
Shallice
and Burgess,1991).A supervisoryattentional system hat
involves he frontal lobesand imbic systemmonitorsongoingactivity and modulates
behaviour
n response o novelty, as n orienting, and when environmentalstimuli
conveyconflicting
nformation.We tested
his
with a behaviouraland electrophysio-
logicalparadigm hat required he monitoringof errors n performance Kaiseret al.,
1997).We utilized a Stroop-like ask
nvolving
a simple wo-choice
eaction ime task
in which a button was
pressed
ccording o the side n which a
green
arrow was
point-
ing
(congruent
ondition).This wascontrastedwith a complex our-choice askwhere
in
addition
to the
green
arrow condition red arrows were randomly
presented,
n
which case he button must be
pressed
n the oppositedirection o the arrow
(incon-
gruent
condition).
Electrophysiological videncehas shown hat following an erro-
neous esponsen a reaction ime task here s a large negative
going
wave at about
100ms, referred to as error-relatednegativity and termed an error detection
wave,
which s not elicited ollowing correct esponses
Falkenstein
t al.,
1990;
Gehring
et
al., 1993).This
negative
wave
s followed
by a
positive
wave hat varieswith a range
of task-related
actors
and
may represent
context
updating, error evaluation and
adjustment f response trategies, n error evaluationwave Falkenstein t al.,1995).
With
hypnosis
he
medium/high usceptibility
roup
showedan increasen errors
on incongruent rials
-
the stroop
nterference
effect
-
but
no
change
n errors on
congruent rials,
whereas
he
performance
of
low susceptiblesemained constant.
Reaction times were not influenced by hypnosis n either
group.
Therefore in
medium/highsusceptibleshere
was a failure to inhibit the automatic response
n
keepingwith
an
nhibition of frontal attentionalcontrol.F{owever,he largenegative
going
error
detectionwaves hat were elicited were non-significantly arger
n Ihe
medium/high han the low susceptibility
roup,
and these
waveswere unalteredby
hypnosis. n other words an error detectionsystemwhich operatesat an early
and
possibly
pre-conscious
tageof
processing
as
not
compromised
y hypnosis; o wit
the unconscious
idden observerof Hilgard, Morgan and
McDonald
(1975).
n con-
trast we found that the positive going error evaluationwave following the error
detection wave was
reduced n
amplitude
with hypnosisbut only in medium/high
susceptibles.
esults or
the
susceptible ubjectsare found in Figure 4. This was
n
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10 Gruzelier
keepingwith
inhibition of a frontal error evaluation
rocess
nd wascompatible
with
the behavioural
data showing a higher error
rate on incongruous rials
in the
medium/high usceptibles
ith hypnosis.
The error detection
wavehasbeen ocalized o a
midline anteriorcingulate
gener-
ator
(Dehaene
et al.,
1994),
a
promising
candidate or
involvement n hypnosis.
he
anterior
cingulate
erforms
executive
unctions hat havebeensubdivided
nto affec-
tive and cognitivecomponents
Devinsky
et al.,
1995).The
cognitive
executive om-
ponent
s involved n response elect ion
n advanceof any
movementand
in
cognitivelydemandingnformationprocessing uchas Stroop nterference,ocalized
by
blood flow imagingand
esionstudies o the anterior cingulate
Pardo
et al.,
1990;
Georgeet a1.,1.993;
endrell et al.,
1995),
nd
by some o the
right
anterior
cingulate
(Bench
et al.,
1993).The affectiveexecutive
unctionsare involved
n regulationof
autonomic
and endocrine
unctions,
assessment
f
motivationalcontext and signifi-
canceof sensory
timuli and emotional
valence.Theseare
mediated hrough exten-
sive
connections
with the amygdalaand
periaqueductal
rey
and autonomic
brainstem
nuclei.
Our
resultshave
ndicated hat the monitoring of
motor
perfor-
mance carried out by the
cognitive executivecomponent
emained
ntact, for the
error
detectionwave and
RTs were unchanged y
hypnosis.Rather t would appear
that
the affect system
nvolving connections ith the
rostral imbic system
ncluding
the amygdala
was unresponsive,
s shown by the absence
of the error evaluation
wave and
apparentlymotivational
nfluences n
performance.
his interpretation
s
also n keeping
with the reducedelectrodermal
rienting activity
reflectinga
reduc-
tion
in amygdaloid xcitatory
modulatory
nfluences.Dissociation etween
cognitive
and
affectiveanterior cingulate
executive ystems
would explain he
increase n the
Stroop
nterference ffect
with hypnosis.
-to.@
-4.@
-6.08
a,Ba
o
a z - g s
4 . S S
pre-hgpnos
i s
-399 -zqq -t80
[ i | | i ieconds
Figure 4. Error detection and
error evaluation
waves in medium/high susceptibles
n hypnosis
and
pre-hypnosis
baseline.
S i t e : C z
h i g h s u s c e p t i b l e s
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Neurophysiologyof hypnosis
11
Left anterior inhibition
Someevidence
has
suggested
hat the anterior nhibition may be laterally asymmetrical
and biased owards
he left hemisphere. his was disclosed y measuring ight and eft
hemisphere
processing
imes
n
dextral subjects
with
a
haptic
object sorting
task com-
paring
eft
and
right hands
Gruzelier
et al.,1984). his was
planned
nitially o validate
asymmetries isclosed y the bilateral
monitoring
of electrodermal
orienting and habit-
uation
processes
escribed
n the next section;n the haptic ask he mediationof hemi-
spheric
nfluences s unambiguously ontralateral.Subjects orted objects
by classwith
eachhand separatelywhile blindfolded.Hand order wascounterbalancednd there
was control
for movement ime. The task was done
prior
to hypnosisand again after
the
hypnotic induction, with susceptibility
monitored
through
the
experiment.
As
shown
n Figure 5 high susceptibles howedan
increase n right hand
processing
imes
with hypnosiswhile there
was no
change
n their left hand times, nor were there bilat-
eral
changesn low susceptibles.
he increase n the
processing
imes of the right hand
(indexing
he left hemisphere) orrelated
positively
with the
hypnotic susceptibility
score.
We replicated he slowing of left hemispheric
processing
with hypnosis n high
susceptibles
n
contrast
o low susceptiblesn a follow-up experiment
with middle aged
subjects,
which was
performed
away from the laboratory and
which included a non-
hypnosis ontrol
group,
(Gruzelier
et al., 1984).The combiningof both experiment
samples isclosed videnceof a
left hemispheric
reference
n high susceptibles t base-
line ashad beenshown
n
the electrodermal
tudyoutlined n the next section.
Left-sided
nhibition of somatosensoryunctionswas
replicated urther by exam-
ining haptic
processing
ith an active-qlertnduction
(Cikurel
and Gruzelier,
1990).
Following
B6nyai
and
Hilgard
(1976)
subjects
edalled
a stationaryexercise
icycle
againsta load and
with instructionsof mental alertness n the hypnotic
nduction.
Dextral subjects
were selectedwith the Barber scale o
form
groups
of
high
an d
medium susceptibles.
ach subject
participated n
two sessions, ne
involving the
conventional
elaxation nduction and the other the active-alert
nduction. n both
conditionsa baseline
measurewas obtainedeither while seatedor while
pedalling.
Session
rder was counterbalanced nd
in each session ypnotic susceptibility
was
monitored to validate the
group
designation
and to compare he induction
proce-
dures,
which n the event
produced
similar
nfluences n susceptibil i ty
r
=
0.79,
post
Hypnoss
pre
Figure
5.
Haptic
processing
times for
right
and
left hands for
pre-hypnosis
baseline and with
hypnosis n high
(left
figure) and
low
(right
figure) susceptibles.
20
(J
o)
3
q)
E
I E
C
,a
c,
(J
o
L
o-
ro
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12
Gruzelier
p
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Neurophysiologyof
hypnosis 13
Patterns
of correlationsbetween he fluency askssupportedan inhibitory influ-
ence
of hypnosiscentring on the left anterior word fluency
performance.
First, the
three
fluency testsdid not correlateat baseline mplying an independence f
func-
tion. Second,
correlationsbetween baselineand hypnosisconditions
were
signifi-
cant for category luency and design luencybut
not for word fluency, n support of
the word fluency
est
alone
being alteredby hypnosis. n contrast,significantcorre-
lations were obtained
with
hypnosisbetween
word
fluency and
both design luency
and category
luency, but not between designand category luency.This could be
interpretedas showing hat an underlyingprocess uch as distributed nhibition
was most at work with word fluency, and while centring on
left
anterior
processes
was also
having some mpact on designand category luency which
involved right
anterior
and left temporal
processing
espectively.Correlations also
showed hat
the
significant elation between eft and right
hand finger tapping dexterity before
hypnosis
was reducedwith hypn osis n kee pingwith a tendency
owards ateral
dissociation.
Anterior disconnectionwith hypnosis n susceptible
ubjectswas recently dis-
closedby
Kaiser n an
unpublished
experiment nvolving EEG topographical
map-
ping
with a 32 electrode
anay n which we examined egionalconnectivitywith EEG
coherence.EEG coherence,
putative
measureof connectivity,was examined
betweenbipolar
pairs
of electrodes. his disclosed significanthypnosis
group
x
condition nteraction n high alphaactivity,asshown n Figure7. In high susceptibles
with
hypnosis here wasa reduction n connectivitywithin the left
prefrontal
egion
specifically
etween eft
lateral
(FP1
and
F7) and medial
F3
and FTCI)
placements
whereas he opposite
effect,namelyan ncreasen connectivitywas ound n low sus-
ceptibles.
n
baseline
here was also a highly significantdifferencebetween
suscepti-
bility
groups
n the direction of
greater
eft anterior connectivity
n high rather than
low
susceptibles.
-I-
?
I
I
prehypnotic
I
I
hypnotio
hish
hypnotic usceptibility
Figure
7. Left anterior EEG coherence n baselineand hypnosis or medium/high and
low sus-
ceptibles
high
shortdistance oherenceepresentsow connectivity nd
viceversa).
o
a
I
o
o
c-l
O
I
I
I
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O
a
a
a
1,4 Gruzelier
Importantly he coherence
esult did not
generalizeo all bandsbut
was estricted
to high alpha
activity.This represents
n EEG band that
relates o cognitive
as dis-
tinct from connative
processing,
ariouslydescribed
s ndexing
high workload, sus-
tained motor
control and long-term
memory
(Mecklinger
and
Bosel, 1989;Sterman
eI a1.,7994; limesche,
996;Burgess nd Gruzelier,
1998).The importance
of selec-
tivity in narrow
band EEG
power
hasalso
been demonstrated y
our differentiating
hypnosis rom baseline
n high and ow susceptibles
Williams
and Gruzelier,
1998).
Summary
Further evidence f a
selectivityof neurophysiological
ction of
hypnosiswas shown
through
examination f anterior
nhibitory nfluences:
the dissociation etween
error detectionand
error evaluation
waves;
the left lateralized nfluences
on haptic
processing,
nd the improvement
n right-
sided
processing
hat wasspecific o
the active-alertnduction;
the specificity
within the left hemisphere
or the effectson
verbal fluency
thal
were restricted
o letter and not semantic
esignated ategories;
the ocalization
f the changes
n EEG coherenceo
within the eft frontal
obe;
the restriction
of the EEG coherence
hangeso the
high alphaband.
These actorsserve o introducea note of caution n attempts o interpret changesn
brain blood
flow and metabolism
n hypnosis,
which
do
not
permit
such
ine
grained
interpretation,
or do they discriminate
etween acilitatory
and nhibitory
unctional
systems.
Right-sided
processing
Focal versusdistributed
nfluencesof hypnosis
have also been
demonstrated
n
experiments
nvestigatinghe
popular
view of right
hemisphericnvolvement
n hyp-
nosis
Pedersen,
984).
Firstly, n our original
experimenton
electrodermal
rienting
and habituation
processes
Gruzelier
and Brow, 1985)
bilateral recording
disclosed
an asymmetry
n the amplitude of
orienting responses
avouring he
right hand in
hypnosisn high
susceptibles
hereas herewasno
reliableasymmetry
n low suscep-
tibles.This
was n contrast
o the baseline ession
where after the
initial tones here
was an asymmetry
avouring he
left hand n high
susceptibles nd again
no reliable
asymmetry
n low susceptibles;
he initial stage
of orienting s thought
o involve
he
right hemisphere,
hich
governs
tatesof broadened
attention,after which
the focal
and selective
ttentionalabilities
of left hemisphere
ake over as would
be exempli-
fied in the
high suseptibles ith their
left
preference
fter
the initial trials
(see
Figure
8).
At the time the
psychophysiologicalxperiment
wasundertaken
he mediationof
hemispheric nfluences
on electrodermal
activity was considered
ontroversial.
Subsequently
he influence
of limbic modulation
has been clarified
by intracranial
stimulation
studies
Mangina
and Beuzeron-Mangina,1996),
hich
have supported
the original
interpretationof
the dominanceof
ipsilateral imbic
modulatory
nflu-
ences n the
passive
rienting
processes
Gruzelier,
1973).Therefore he
resultsmay
be interpretedas showinga left hemispheric referencen high susceptiblest base-
line. While this
resultwasnot
predicted
and ran counter
o right hemisphericity
heo-
ries of hypnotic susceptibi l i ty,
upport was
forthcoming rom
the subsequent
investigation f
lateralized aptic
processing
escribed bove
Gruzelier
et al.,
1984).
Suchbaseline
eft hemispheric dvantages
ay
simply eflect
greater
cognitiveagility
-
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-3.0
-1. ,
Log.
Amplitude
109.
AmDlitude
-3.0
-) .5
-4.0
SUSCEPT
BLE
l0
Trlal
Log.
Amplltude
Log.
Amplitude
Neurophysiologyof hypnosis
15
UNSUSCEPTIELE
_Len
-3.0
-7. '
-4.0
l0
Trial
-3.0
-3.'
l0
Irial
l0
Irial
Figure8. The amplitude f bilateral lectrodermalrienting esponseshowingeversal f
asymmetryrombaseline
tones)
o hypnosisn highsusceptiblesnd
no consistenthangesn
lowsusceptibles.
in line with task demands y high susceptibles
Crawford,
1989).Accordingly
t
would
appear
hat it was the hypnotic nduction hat
instated he right hemispheric
functional
preference
n susceptible ubjects.
An enhancement
f right
posterior
unctionswas ound in an experiment
nvolv-
ing the divided visual
ield
presentation
f flashes equiring brightness
udgements.
The experiment nvolved hree sessions
n
the order
baseline, ypnosis, aseline.
t
wasconducted
with
eyesopen
with sufficient rials o
perform
signaldetection
analy-
sis to
give
estimatesof
perceptual
sensit iv i ty
ndependentof cognit ive bias
(McCormackand Gruzelier,1993).Blocksof trialswere nterspersed ith a live hyp-
notic
induction.
Susceptibility
was monitored throughout
he experimentwith sub-
jects
divided nto medium and high susceptibles.
esultsare shown n Figure 9.
Perceptual ensitivity
was
ound
to be enhancedn the hypnosis onditioncompared
with the control conditions.Comparisonof the susceptibility
roups
ndicateda
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1,6 Gruzelier
bilateral
increase n
perceptual
sensitivity n medium susceptibles
hereas n high
susceptibleshere was no change n susceptibility
n
the left hemisphere
right
visual
field) in contrast o a focal right hemisphericenhancement
left
visual field). An
improvement n
perceptual
ensitivity s according o signaldetection heory
ndica-
tive of an ncreasen signal o noise atio aswill occur
with
a
reduction n central ev-
els of arousal.Analysis of the
cognitivebias variableshowed hat
judgements
were
more conservativeor the right hemispherehan
the left for the
group
as a whole
(p
left asymmetryat the temporal
location
(electrodes
3l4) in the
medium/high
group.
n contrast here was an oppo-
site eft>right asymmetry n the story
condition of medium/high usceptibles,
s well
as n both
the conditions f the low susceptibles.his
reversal f asymmetry o favour
the right hemisphere
n
susceptible
ubjects id not extend o the
lateral central
(C314) lacements.
he resultsdemonstratedhat
right
anterior
emporal obe activ-
ity was
aised n medium/high usceptibles ith hypnosis.
LHem.
.
---.---
RHem.
)
xigtt
.a.
-.-....
LHem.
.
., ''
' ''
nHem.
l
Medium
fr;;;':'il:L--
Control Hypnosis
Control
Figure9.
Visual
sensitivity
n baseline ontrolconditions ndhypnosis
n high and mediumsus-
ceptibles
or left
and
right hemispheres.
-
8/19/2019 Gruzelier CH 1998 Working Model
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o
a
a
a
a
Neurophysiology
of hypnosis
l7
Summary
The asymmetries
n electrodermal
rienting esponses
nd he cortical
evoked
poten-
tial
N100,both to auditory
stimuli
presented
uring
the latter
part
of the
induction
(Gruzelier
and
Brow, 1985; utai
et al., 1993),
ndicatea shift
n the balance f
tempo-
ral-limbic activity to
favour the
right hemisphere.
n contrast he asymmetry
of
visual
sensory ensitivity
ssessed
ith signaldetection
analysis
McCormack
and Gruzelier,
1993)depicted
an enhancement
f right
hemispheric
rocessing
n high susceptibles
and
no change
n
the
left hemisphere
whereasmedium
susceptibles
howedbilateral
improvement.
Conclusion
This seriesof experiments
has shown
a number
of reproducible
changes
n brain
function that distinguished
medium/highsusceptibles
fter
instructionsof
hypnosis
both
from their baseline
tateand
from low susceptibles.
he attempts
were
modest
in scopeand
must be confined
o the
traditional
hypnotic
relaxation nduction.
Continuing
support
was
provided
or associations
etween
hypnosis nd:
activationof
anterior
ronto-limbic nhibitory
processes,
anterior
inhibition or disconnection,
either
lateralized to
left hemispheric
egions
or
bilateraldepending
n the
processes
xamined,
involvementof right temporoposterior rocessing,
evidence f superior
attentional
abilities
n high susceptibles,
evidence
of
poor
attentional
abilities
n unsusceptible
ubjects
with
progressive
improvement
hrough he
nduction,and
.
no evidence
f right
hemisphericity
n the baseline
tate n susceptible
ubjects.
Across
electrodermal,
lectrocortical
nd behavioural
domains
susceptible
ubjects
evinced
nhibitory influences
n attention
with hypnosis
whereasunsusceptible
ub-
jects
mproved attentional
performanceas the
induction
progressed.
vidence
was
also
ound for bilateral
alterationsof
function
in medium susceptibles
n situations
where
changes
n high susceptibles
ere
ateralized, uggesting
more diffuse
or dis-
tributed
changes
n mediumsusceptibles
nd
more focal changes
n high susceptibles.
Together hese esultsndicate he importanceof stratifyinggroups nto low, medium
and
high susceptibles.
In our neuropsychological
ranslation
of the
traditional
hypnotic
nduction,
hyp-
nosiswas
nitiated by engaging
nterior executive
ontrol
systems.
side from alter-
ations
n cortical
functions along anterior-posterior
nd
lateral axes, hese
will
orchestrate
op
down changes
nfluencing halamic
and brain
stem
mechanisms.
Currently
there
is renewed
nterest
n
the
electrophysiology
f thalamocortical
mechanisms
n
perceptual
binding,conscious
erception
and altered
statesof aware-
ness
Llinas
and
Pare, 1991;Singer,
1993).Llinas,
Ribary, Joliot
and Wang
(1994)
have
proposed
hat
consciousness
s a noncontinuous
event determined
by
simul-
taneity
of activity
in specific
halmocortical
nuclei, which
provide
the
content of
experience,
nd he
non-specific iffuse
halamic
projectionsystem hat
provides he
contextand alertness.n this regard he anteriorand posteriorcingulateappearof
particular
promise
n the top down
control of
thalamicactivity
relevant
o hypnosis.
Devinsky,
Morrell and Vogt
(1995)
have
remarked
One
of the unique
features
of
anterior
cingulate
cortex circuitry
is its diverse
halamic afferents
and consequent
ability
to sample
nputs from more thalamic
nuclei
than any other
cortical
region.
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8/19/2019 Gruzelier CH 1998 Working Model
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18
Gruzelier
The ability to sample rom a wide
range
of thalamic
nputsmay
be crucial
or its con-
tributions o
motor response election unctions.
p
280.'The samecould be said or
conative unctions and the l imbic thalamus
Bentivoglio
et al.,
1993).Hypnosis
researchwould benefit
from
examining he
interplay
between
cortical and thalamo-
cortical systems,
or which
the
methodology
of
fast frequencyEEG transients olds
much
promise.
In Llinas'smodel dreaming s regardedas a stateof hyperattentivenesso
intrin-
sic activity without the registrationof sensory
nput,
a state
with
an obvious
affinity
with hypnosis. his serves o acknowledgehat the dreamanalogy emainsappealing
for aspects f the
hypnotic
experience.Consider
Fuster's
1995)
descriptionof cog-
nitive featuresof dreaming,which
include
he altered senseof
time and absence f
temporality, he lack of
guiding reality
and critical
udgement,
he anchoring
n
per-
sonal experience, ffectivecolouring, dissociation
rom sensory nput and context.
'The
fragmentednetworks
activated
n
the dream
seem o lack the associativeinks
to a
time frame, anchoredas they are in the
present,
without time tags and
refer-
ences.'
This could equallybe a descriptionof the hypnotic stateas
high
susceptibles
experience
t.
As
the studiesunfoldeda
selectivityof centralaction ncreasingly ecamea
hall-
mark
of
hypnosis
providing
undeniableevidenceof neurophysiological hanges
n
susceptible ubjects,
which
distinguished
hem from unsusceptible ubjects.
As
Schopenhaueremarked
All
truth
passes
hrough
three stages. irst it is ridiculed.
Secondt is violently opposed. hird it is accepted sbeing self-evident'. pplication
of the rapid advances
n
cognitive
neuroscience
o
hypnosis esearchmay make the
reality of the third
stageevermore ikely.
Acknowledgements
The researchwassuppported y the Saugstad
und,
he
Institut fiir
Grenzgebiete
er
Psychologie nd
Psychohygienend studentshipsrom the Medical
Research
Council
and he Wellcome
Trust.
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Address
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Professor
J
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Department
of Behavioural
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Imperial
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St Dunstans
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London
W6 8RF, UK