Gruzelier CH 1998 Working Model

8/19/2019 Gruzelier CH 1998 Working Model

1/19

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.


2/19

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


4/19

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


5/19

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


6/19

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.


7/19

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


9/19

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


10/19

12

Gruzelier

p


11/19

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


12/19

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


13/19

-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


14/19

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.


15/19

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.


16/19

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

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St Dunstans

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W6 8RF, UK

Gruzelier CH 1998 Working Model

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Transcript of Gruzelier CH 1998 Working Model