406261

Review ArticleNeurophysiological Effects of Meditation Based onEvoked and Event Related Potential Recordings

Nilkamal Singh and Shirley Telles

Patanjali Research Foundation, Patanjali Yogpeeth, Haridwar, Uttarakhand 249405, India

Correspondence should be addressed to Shirley Telles; [email protected]

Received 28 November 2014; Revised 28 January 2015; Accepted 8 February 2015

Academic Editor: Carlo Miniussi

Copyright 2015 N. Singh and S. Telles. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.

Evoked potentials (EPs) are a relatively noninvasive method to assess the integrity of sensory pathways. As the neural generators formost of the components are relatively well worked out, EPs have been used to understand the changes occurring duringmeditation.Event-related potentials (ERPs) yield useful information about the response to tasks, usually assessing attention. A brief review ofthe literature yielded eleven studies on EPs and seventeen on ERPs from 1978 to 2014. The EP studies covered short, mid, andlong latency EPs, using both auditory and visual modalities. ERP studies reported the effects of meditation on tasks such as theauditory oddball paradigm, the attentional blink task, mismatched negativity, and affective picture viewing among others. Both EPand ERPs were recorded in several meditations detailed in the review. Maximum changes occurred in mid latency (auditory) EPssuggesting that maximum changes occur in the corresponding neural generators in the thalamus, thalamic radiations, and primaryauditory cortical areas. ERP studies showed meditation can increase attention and enhance efficiency of brain resource allocationwith greater emotional control.

1. Introduction

Meditation has been described as a training in awarenesswhich over long periods of time produces definite changesin perception, attention, and cognition. The neurophysio-logical correlates of meditation have been determined byelectrophysiological recordings (from the 1960s to the presenttime) and more recently by neuroimaging studies (fromthe 1980s till the present time). Among electrophysiologicalvariables sensory evoked potentials (EPs) provide a relativelynoninvasive way of studying changes in specific sensorypathways during meditation [1]. It is believed that meditationalters cortical functioning and corticofugal controls whichmay significantly modify the processing of information atbrainstem and thalamic levels [24]. Hence short, mid, andlong latency EPswould be expected to helpmap changes fromthe brainstem up to the association or secondary corticalareas [5]. The present review was undertaken to determinewhich modalities and latencies of EPs were recorded inmeditation and the conclusions derived.

EPs are evoked spontaneously with repetitive sen-sory stimulation and can provide information about brain

resource allocation and the speed of stimulus processing,whereas event-related potentials (ERPs) are not spontaneousbut elicited with cognitive task processing [68]. Hence ERPscan provide additional information regarding the discrim-inative ability of the brain and neurocognitive processingrelated to shifting attention.The present review also discussesstudies which evaluated the effect of meditation on differentmodalities of ERPs.

2. Methods

2.1. Search Strategy for Meditation and Evoked PotentialStudies. Thedatabase searched was PubMed using the searchwords Meditation, Evoked Potentials. Fifty-eight citationswere obtained from PubMed. To be included in this reviewarticles had to be written in English (8 articles were excludedas they were written in other languages). Articles wereexcluded from the review if (i) they reported event-relatedpotentials (ERPs) rather than EPs (19 articles were excludedfor this reason) and (ii) they did not deal directly withthe subject of meditation (5 articles were excluded for thisreason), (iii) the articles were not experimental studies but

Hindawi Publishing CorporationBioMed Research InternationalVolume 2015, Article ID 406261, 11 pageshttp://dx.doi.org/10.1155/2015/406261

2 BioMed Research International

were review articles or descriptive (5 articles were excludedfor this reason), and (iv) the study recorded variables otherthan EPs such as EEG, MRI, and spectroscopy studies(10 articles were excluded for this reason). Eleven articlesreported evoked potential changes in different meditationsand are reviewed here for their study design, method ofmeditation, and conclusions derived.

2.2. Search Strategy forMeditation and Event-Related PotentialStudies. The databases searched were PubMed using thesearch words Meditation, Event-Related Potentials. Sixtycitations were obtained from PubMed. To be included in thisreview articles had to be written in English (8 articles wereexcluded as they were written in other languages). Articleswere excluded from the review if (i) they reported evokedpotentials (EPs) rather than event-related potentials (ERPs)(15 articles were excluded for this reason) and (ii) they didnot deal directly with the subject of meditation (3 articleswere excluded for this reason), (iii) the articles were notexperimental studies but were review articles or descriptive(5 articles were excluded for this reason), and (iv) the studyrecorded variables other than ERPs such as EEG, MRI,and spectroscopy studies (11 articles were excluded for thisreason). Details of one study were not available. Seventeenarticles reported event-related potential changes in differentmeditations and are reviewed here for their study design,method of meditation, and conclusions derived.

2.3. Method of Review. The whole papers were obtained andthe details related to (i) stimulus modality for EPs or natureof the ERP, (ii) sweep width or latency of the EPs, (iii) type ofmeditation, (iv) study design, and (v) changes (if any) in EPor ERP components and the corresponding changes in theneural generators were noted.

3. Results

3.1. Details of the Evoked Potential Studies. Out of the elevenstudies 10 used auditory stimuli while one used visual stimuli.With regard to sweep width out of the nine studies tworeported short latency EPs, four mid latency EPs, two longlatency EPs, and one long latency visual evoked potential(LLVEP) and there were also two combinations of (i) shortlatency and mid latency auditory EPs and (ii) short, mid, andlong latency auditory EPs. Details about the components ofEPs are given in Table 1.

The meditation techniques studied were all eyes closedpractices; two were transcendental meditation (TM), twoQigong, five meditations on the Sanskrit syllable OM, one amoving meditation called cyclic meditation, and one Sahajayogameditation.Apart from themovingmeditation the othereight techniques directed the thoughts in a fixed pattern forall practitioners towards either a single syllable or phraseor a set of thoughts. In the moving meditation as well, thesequence of thoughts was fixed and played on a CD [9].

Hence in all the studies the meditation techniquesinvolved directing the attention in a specific way in allpractitioners.The next point considered was the study designwhich included the controls used.

The range of experience in meditation was from nave totwenty years.The sample size variedwidely in the nine studieswith a range between five and sixty practitioners and groupaverage S.D. was 27.8 18.4.

3.2. Details of the Event-Related Potential Studies. Out ofthe seventeen studies four used auditory oddball paradigm,three used the attentional blink task, two used mismatchednegativity, two used affective picture viewing, one usedglobal-to-local target task, one used the Stroop task, oneused visual A-X continuous performance task, one usedrow/column speller, one used anticipatory and pain evokedERPs, and one used discrimination of the imagery of the handmovement.

The meditation techniques used were Vipassana medita-tion in six studies, Sahaja yoga meditation, open monitoringmeditation, Sudarshan Kriya yoga meditation, musical med-itation, meditative mindfulness, cyclic meditation, mindful-ness based cognitive therapy one each in seven studies, andtwo mixed traditions and 2 did not specify the meditationtechniques used. All meditation techniques were performedwith eyed closed.

3.3. Observations Common to Both EP and ERP Researchin Meditation. In meditation research it is often difficult tofind an appropriate control group which does not practicemeditation but is otherwise comparable to the meditationgroup in other ways. This is because meditators often haveother changes in their lifestyle such as abstaining fromcaffeine, nicotine, and other stimulating substances, differenthours of rising and sleeping, and other differences. For thisreason in some studies themeditators themselves are assessedunder identical conditions on another day as a control, whichmay be described as the self-as-control [10].

This design was followed in four of the EP studies whichare presented in Table 2 [5, 1113]. There were two singlegroup studies [1, 14].These were the earliest studies on evokedpotentials and meditation. The absence of a comparison orcontrol state or group is an obvious disadvantage, as theeffect of time during a session can be expected to influencethe evoked potential components and the meditation effectwould not be separated from this. In five other papers [1519]the approach taken was to have separate groups of partici-pants. In only one trial [17] the participants were randomizedas three groups. The advantage of the separate groups designover the self-as-control is that nonmeditators would not getinadvertently into meditation which is a disadvantage of theself-as-control design, where experiencedmeditatorsmay getinto the meditative state automatically, even during a controlsession.

Out of the seventeen ERP studies, 12 studies had a two-group design, four studies had a self-as-control design, andone had mixed design in which the study was conductedin two phases, phase 1 was a cross sectional study andphase 2 was a longitudinal study. This is described in Table 3.The disadvantages and advantages are comparable to thosedescribed above for EP studies. With ERP studies there isan additional point; since the participants are given a task

BioMed Research International 3

Table 1: Neural generators of evoked potential components.

S. number Name of thecomponentsLatencies(msec) Neural generators

1 Short latency auditoryevoked potential

Wave I 1.9 Auditory portion of the eighth cranial nerve

Wave II 3.6 Near or at the cochlear nucleus. A portion from the eighth nerve fibersaround the cochlear nucleusWave III 4.2 The lower pons through the superior olive and trapezoid bodyWave IV 5.2 The upper pons or lower midbrain, in the lateral lemniscus and the inferior

colliculus; a contralateral brainstem generator for wave V is suggestedWave V 5.8Na 1419 Medial geniculate bodyPa 2532 Superior temporal gyrus

2 Mid latency auditoryevoked potential

Nb 3565 Dorso-posterior-medial part of Heschls gyrus that is the primary auditorycortexN1 4060ms Secondary auditory cortex in the lateral Heschls gyrusP1 80115ms Bilateral parts of the auditory superior cortex

Long latency auditoryevoked potential

N2 140180ms Mesencephalic-reticular activating system (RAS)P2 220280ms Anterior cingulate cortex

it is usual to record before and after meditation, not duringmeditation, as doing the taskwould interferewithmeditation.

3.4. Results of EPs

3.4.1. Auditory Evoked Potentials. Discussing the shortlatency or brainstem auditory evoked potentials first, therewere three studies. In the earliest study [14] the peak latencyof wave V which corresponds to the inferior colliculus variedwith the intensity of the stimuli and hence could not beconsidered as an effect of the transcendentalmeditation (TM)practiced. In the second study which reported short latencyauditory evoked potentials in Qigong meditators [15] therewas a significant increase in the peak amplitudes of waves I toV of short latency auditory evoked potentials. An increase inamplitude is suggestive of recruitment of increased neuronsin the underlying neural generators [20]. This suggested thatQigong meditation activates areas in the brainstem. Therewas no change in short latency auditory evoked potentialsin patients with epilepsy who practiced Sahaja yoga possiblybecause they were novices to meditation [17]. In the otherstudy which reported changes in short latency auditoryevoked potentials the peak latency of wave V increasedduring random thinking, focusing and meditative focusing,but not during meditation [11]. An increase in peak latencysignifies delayed transmission through the respective neuralgenerators [5], in this case located in the brain stem. Hence itwould appear as if random thinking, focusing, andmeditativefocusing all delay auditory information transmission at thebrainstem level but this does not happen during meditationon OM.

Themid latency auditory evoked potentials correspond toneural generators in the thalamus, primary auditory cortex,andHaschls gyrus [24].WithQigongmeditation the ampli-tudes of Na and Pa components decreased during meditation[15]. The Pa wave peak amplitude also decreased duringmeditation on OM in sixty practitioners [12] but there was

an increase in peak amplitude of Na wave during meditationon OM in a separate study [18]. The Na wave is believed tobe due to activity at the mesencephalic and diencephalic level[21] and the Pa wave corresponds to activity at the superiortemporal gyrus [22]. A third component of the mid latencyauditory evoked potentials is the Nb wave.This wave appearsrelatively localized in the dorso-posterior-medial area ofHeschls gyrus, that is, the primary auditory cortex [23]. TheNb wave peak amplitude increased and peak latencies of Paand Nb waves decreased after the moving meditation calledcyclic meditation (CM), which incorporates movement [5].The peak latency of Nb wave reduced during meditationon OM as well [19]. Hence the moving meditation alteredthe auditory pathway at the level of superior temporal gyrusand Heschls gyrus with a delay in auditory transmissiondespite an increase in number of neurons recruited. Duringmeditation on OM the delay in auditory transmission wasfound only in the dorso-posterior-medial area of Heschlsgyrus.

Long latency auditory evoked potentials showed nosignificant change in an early study on transcendentalmeditation practitioners [1]. The P2 component showed adecrease in peak amplitude during Qigong meditation anda decrease in peak latency during meditation on OM. TheP2 wave partly reflects auditory output of the mesencephalicactivation system [24, 25]. From MEG and EEG data basedon depth electrodes in patients, the neural generators for theP2 componentwere localized in the planum temporale as wellas the auditory association complex (Brodmann area 22) [2629]. Also it is speculated that the P2 component may receivecontributions from cortical areas in the depth of the Sylvianfissure. Hence this area, which is associated with complexauditory functions, changes during both Qigong and OMmeditations.

3.4.2. Summary of Changes in Auditory Evoked Potentials.Out of the four studies which evaluated short latency auditory


Table2:Detailsof

thee

vokedpo

tentialstudies.

S.nu

mber

Reference

Mod

ality

audi-

tory/visu

al/som

atosensory

andlatency

Type

ofmeditatio

nMeditatio

nexperie

nce,du

ratio

nCom

ponentsa

lteredandbrain

area

Samplea

nddesig

n

1

Electro

enceph

alogr

Clin

Neuroph

ysiol.

1978,45(5):

671673[1]

Auditory

Long

latency

Transcendentalmeditatio

n18

mon

thsto6years

Nosig

nificantchange

Sing

legrou

p

2

Intern

JNeuroscience.

1980,10(2-3):

165170[14

]

Auditory

Shortlatency

Transcendentalmeditatio

n6to

9years

WaveV

latencyincreasedin

mod

erateintensitystimuliand

waveV

latencydecreasedin

high

intensity

stimuli

Sing

legrou

p

3Am

JChinMed.

1990,18(3-4):

95103

[15]

Auditory

Shortlatency,m

iddle

latency,and

long

latency

Qigon

gmeditatio

nwhich

involves

theinitia

lconcentrating,

asub

sequ

ent

circ

ulating,

andfin

ally

thedispersio

nof

Qi

1to20

years

Therew

asas

ignificantincrease

inam

plitu

dein

waveI-V

ofBA

ER,N

aand

Pawaveo

fMLR

decreased,andP2

waveo

fLL

AER

also

decreaseddu

ring

meditatio

n

3grou

ps:B

AER

,MLA

ER,and

LLAER

4Am

JChinMed.

1993,21(3-4):

243249[16]

Visual

Corticalevoked

potentials

Qigon

gmeditatio

nin

which

the

practitionerc

oncentrateso

nthe

Dantian

2.3yearsfor

the

experie

nced

grou

p,1.9

mon

thsfor

the

learning

grou

p

Peak-to

-peakam

plitu

deof

N80-P115-N150and

N150-P2

00-N

280increasedin

thee

xperienced

grou

p

3grou

ps:practition

ergrou

plearning

grou

p,andcontrolgroup

5IntJ

Neurosci.

1994;76(1-2):

8793[18]

Auditory

Middlelatency

evoked

potentials

OMm

editatio

nin

which

the

participantsmeditatedwith

effortless

absorptio

nin

thes

ingle-thou

ghtstateof

theo

bjecto

fmeditatio

n,thatis,

OM.

10years

Experie

nced

meditatorshad

significantincreaseinpeak

amplitu

deof

Naw

aved

uring

meditatio

nandsig

nificant

redu

ctionin

Naw

avep

eak

amplitu

dedu

ringcontrolsessio

n

Two-grou

pstu

dy(experienced

meditators

andno

nexperienced)

6Indian

JMed

Res.

1993;98:2379[19

]

Auditory

Middlelatency

evoked

potentials

OMm

editatio

nin

which

the


effortless

absorptio

nin

thes

ingle-thou

ghtstateof

theo

bjecto

fmeditatio

n,thatis,

OM.

520

years

Experie

nced

meditatorshada

significantreductio

nin

thep

eak

latencyof

theN

bwave

Two-grou

pstu

dy(experienced

meditators

andno

nexperienced)

7

Appl

Psycho

physiol

Biofeedb

ack.2000,

25(1):112

[17]

Auditory

BAEP

MLA

EP

Sahajayoga

inwhich

thep

articipants

makec

ertain

mentalassertio

nsby

placing

theh

andon

different

partso

fthe

body.

Not

experie

nced

=10

(Sahajay

ogag

roup

),

=10

(mim

icking

exercise

grou

p),and

=12

(con

trolgroup

)

Sign

ificant

increase

inNa-Pa

amplitu

deof

MLR

following

meditatio

npractice

Rand

omized

controlled

study

8Clin

EEG

Neurosci.2009,40

(3):190

195[5]

Auditory

Mid

latency

Cyclicm

editatio

nin

which

aserieso

fasanas

(posturesinterspersedwith

relaxatio

ntechniqu

es)arepracticed

with

awareness.

648

mon

ths

Afterc

yclic

meditatio

ntherew

asas

ignificantincreaseinthep

eak

latencyof

theP

awavea

ndof

the

Nbwave;peak

amplitu

deof

the

Nbwavea

lsoincreased

Selfas

controldesign


Table2:Con

tinued.

S.nu

mber

Reference

Mod

ality

audi-

tory/visu

al/som

atosensory

andlatency

Type

ofmeditatio

nMeditatio

nexperie

nce,du

ratio

nCom

ponentsa

lteredandbrain

area

Samplea

nddesig

n

9IntJ

Yoga.20103

(2):374

1[11]

Auditory

Brainstem

auditory-evoked

potentials(BAEP

s)

OMm

editatio

nin

which

the


effortless

absorptio

nin

thes

ingle-thou

ghtstateof

theo

bjecto

fmeditatio

n,thatis,

OM.

6mon

ths

WaveV

peak

latency

significantly

increasedin

cancalata,ekagrata,and

dharana,

butn

ochange

occurred

durin

gthed

hyanas

essio

n

Selfas

control

10Clin

EEG

Neurosci.2012,43

(2):154

60[12]

Auditory

Mid

latency

OMm

editatio

nparticipantswere

instructed

tokeep

theire

yesc

losedand

dwellonthou

ghtsof

OM,w

ithou

tany

effort,particularlyon

thes

ubtle

(rather

than

physical)attributes

and

conn

otations

ofthes

yllable.

660

mon

ths

Sign

ificant

increase

inthep

eak

latencieso

fNaa

ndPa

waves

durin

gmeditatio

nandthep

eak

amplitu

deof

Pawavew

assig

nificantly

decreaseddu

ring

meditatio

n

Selfas

controldesign

11Clin

EEG

Neurosci.2014,pii:

1550059414544737

[13]

Auditory

Long

Latency

OMm

editatio

nin

which

participants

wereinstructedto

keep

theire

yesc

losed

anddw

ellonthou

ghtsof

OM,w

ithou

tanyeffort,particularlyon

thesub

tle(ratherthanph

ysical)attributes

and

conn

otations

ofthes

yllable.

660

mon

ths

Decreaseinthep

eaklatencyof

theP

2waved

uringandafter

meditatio

nSelfas

controldesign


Table3:Detailsof

eventrelated

studies.

S.nu

mber

Citatio

nParticipants

Natureo

fthe

ERP

task

Design

Interventio

nFind

ings

1Neuroscience.2014,

281C:195201

[31]

Health

yexperie

nced

meditatorsand

nonm

editators

Affectivep

icture

view

ing

Two-grou

pstu

dy

Nointerventio

nwas

given

butthisstudy

compared

betweenlong-te

rmexperie

nced

Sahajayoga

meditatorsand

nonm

editators

Mid

latency(14

0400m

s)ER

Pswerea

ttenu

ated

forb

othpo

sitivea

ndnegativ

epicturesa

ndas

tronger

ERPnegativ

ityin

the

timew

indo

w200

300m

swas

foun

din

meditatorsregardlessof

picturev

alence.W

eassum

ethat

long-te

rmmeditatio

npracticee

nhancesfrontaltop-do

wncontroloverfastautom

aticsalience

detection,basedon

amygdalafunctio

ns.

2IntJ

Psycho

physiol.

2013,90(2):207214[32]

Health

yexperie

nced

meditatorsaged

206

1years

Auditory

oddb

all

task

with

twotones

(stand

ardandtarget)

One

grou

pwas

assessed

intwoseparate

cond

ition

s(selfas

control)

Vipassanam

editatio

nand

rand

omthinking

TheV

ipassana

expertssho

wed

greaterP

3bam

plitu

destothetargetton

eafterm

editatio

nthan

they

didbo

thbeforemeditatio

nandafter

then

o-meditatio

nsession.Th

eseresultssuggestthat

expertVipassanam

editatorsshow

edincreasedattentionalengagem

entafterm

editatio

n.

3SocC

ognAffect

Neurosci.2013,8

(1):

100

111[34]

Health

yVipassana

meditatorsEx

p.=

2.540

years

Three-stimulus

auditory

oddb

alltask

One

grou

pwas

assessed

intwoseparate

cond

ition

s(selfasc

ontro

l)

Vipassanam

editatio

nand

instr

uctedmindwanderin

g

Meditatio

ncomparedto

controlcon

ditio

nhaddecreasedevoked

delta

(24

Hz)po

wer

todistr

acterstim

ulicon

comitantlywith

agreater

event-r

elatedredu

ctionof

late(500

900m

s)alph

a-1(810Hz)activ

ity,w

hich

indexedaltereddynamicso

fatte

ntionalengagem

entto

distr

acters.A

ddition

ally,

stand

ardstimuliw

erea

ssociatedwith

increasedearly

event-r

elated

alph

aphase

synchron

y(in

tertria

lcoh

erence)and

evoked

theta(

48H

z)ph

ases

ynchrony,

suggestin

genhanced

processin

gof

theh

abitu

ated

stand

ardbackgrou

ndstimuli.Finally,during

meditatio

n,therew

asag

reater

differentialearly-evokedgammap

ower

tothed

ifferentstim

ulus

classes.C

orrelatio

nanalysisindicatedthatthiseffectstemmed

from

ameditatio

nsta

te-related

increase

inearly

distr

acter-evoked

gammap

ower

andph

ases

ynchrony

specifictolonger-te

rmexpertpractitioners.Th

efind

ings

suggestthatV

ipassana

meditatio

nevokes

abrain

stateof

enhanced

perceptualcla

rityanddecreasedautomated

reactiv

ity.

4Fron

tHum

Neurosci.

2012,6:133

[38]

Health

ymeditators

andno

nmeditators

Global-to-local

targettask

Stud

ycond

uctedin

two

phases

Phase1:crosssectional

study

Phase2

:lon

gitudinal

study

Openmon

itorin

gmeditatio

n

Meditatorsshow

edan

enhanced

processin

gof

targetlevelinformation.In

contrastwith

control

grou

p,which

show

edalocaltargetselectioneffecto

nlyin

theP

1and

aglobaltargetselectio

neffectintheP

3compo

nent,m

editatorsshow

edeffectsof

localinformationprocessin

gin

theP

1,N2,andP3

andof

glob

alprocessin

gforthe

N1,N2,andP3

.Thus,m

editatorsseem

todisplay

enhanced

depthof

processin

g.In

thelon

gitudinalexperim

ent,meditatio

nmod

ulates

attentionalreadyafter

a4-day

meditatio

nretre

at.Together,theseresultssuggestthatp

racticingmeditatio

nenhances

thes

peed

with

which

attentioncanbe

allocatedandrelocated,thus

increasin

gthed

epth

ofinform

ationprocessin

gand

redu

cing

respon

selatency

5SocC

ognAffect

Neurosci.2013,8

(1):

8592[45]

Health

ymeditators

andno

nmeditators

Stroop

task

Two-grou

pstu

dy

Com

paris

onbetween

meditatorsand

nonm

editators,m

editators

arefrom

vario

ustradition

s

Meditatorsshow

edgreatere

xecutiv

econ

trol(i.e.,fewer

errors),ah

ighere

rror

relatednegativ

ity(ERN

),andmoree

motionalacceptancethancontrols.

6BM

CPsychiatry.2012,

12:15[44]

Patientsw

ithbipo

lar

disorder

andno

rmal

healthyparticipants

AvisualA-X

continuo

usperfo

rmance

task

Two-grou

pstu

dyMindfulnessbasedcogn

itive

therapy(M

BCT)

MBC

Tin

bipo

lard

isorder

improved

attentionalreadinessandattenu

ated

activ

ationof

nonrele

vant

inform

ationprocessin

gdu

ringattentionalprocesses

7JN

euralE

ng.2011,8(2):

025019

[42]

Health

yindividu

als

Row/colum

nspeller

task

Two-grou

pstu

dyMeditativ

eMindfulness

Indu

ction(M

MI)and

non-MMIcon

trolgroup

MMIsub

jectsw

eres

ignificantly

morea

ccuratethancontrolsub

jectsa

ndthey

prod

uced

significantly

larger

P300

amplitu

desthancontrolsub

jectsa

tCza

ndPO

7

8NeurosciR

es.2011,71

(1):444

8[46]

Health

ymeditators

andno

nmeditators

Emotionalloadof

stimuli(IAPS

pictures)

Two-grou

pstu

dy

Nointerventio

nwas

given

butthisstudy

compared

with

experie

nced

meditators

andno

nmeditators

Theresultsho

wed

different

emotionalprocessingin

meditatio

npractitioners:ath

ighlevelsof

processin

gmeditatorsarelessa

ffected

bystimuliw

ithadversee

motionalload,whileprocessin

gof

positives

timulirem

ains

unaltered

9Pain.2010,150(3):

428438[47]

Health

ymeditators

andno

nmeditators

Anticipatoryand

pain-evokedER

PsTw

o-grou

pstu

dy

Nointerventio

nwas

given

butthisstudy

compared

with

experie

nced

meditators

andno

nmeditators;

meditatorswerefrom

different

tradition

s

Meditatio

nredu

cesthe

anticipationandnegativ

eapp

raisa

lofp

ain


Table3:Con

tinued.

S.nu

mber

Citatio

nParticipants

Natureo

fthe

ERP

task

Design

Interventio

nFind

ings

10JN

eurosci.2009,29

(42):1341813427

[37]

Health

ymeditators

andno

nmeditators

Attentionblinktask

andattention

auditory

task

Two-grou

pstu

dyVipassanaa

ndloving

kind

nessmeditatio

n

Threem

onthso

fintensiv

emeditatio

ntraining

redu

cedvaria

bilityin

attentionalprocessingof

targettonesa

ndredu

cedreactio

ntim

evariability.Th

oseind

ividualswith

greatestincrease

inneuralrespon

seconsistency

hadlargestd

ecreaseinbehavioralrespon

sevaria

bility.Re

duced

varia

bilityin

neuralprocessin

gwas

observed

regardlessofwhether

thed

eviant

tone

was

attend

edor

unattend

ed.

significantly

affectatte

ntionandbrainfunctio

n.

11Con

fProcIEE

EEn

gMed

BiolSoc.2008,

2008:6626

65.[48]

Meditatorsand

nonm

editators

Disc

riminationof

theimaginativeh

and

movem

entand

the

idlesta

te

Two-grou

pstu

dyType

ofmeditatio

nno

tspecified

Them

editatio

npracticec

anim

provethe

classificatio

naccuracy

ofEE

Gpatte

rns.Th

eaverage

classificatio

naccuracy

was

88.73%

inthem

editatio

ngrou

p,whileitwas

70.28%

inthec

ontro

lgrou

p.Anaccuracy

ashigh

as98.0%was

achieved

inthem

editatio

ngrou

p.

12IntJ

Psycho

physiol.

2009,72(1):516

0.[33]

Health

yexperie

nced

meditators

Auditory

oddb

all

task

with

twotones

(stand

ardandtarget)

One

grou

pwas

assessed

intwoseparate

cond

ition

s(selfas

control)

Vipassanam

editatio

nand

rand

omthinking

Duringmeditatio

nN1amplitu

defro

mthed

istracter

was

redu

cedfro

ntally;P

2am

plitu

desfrom

both

thed

istracter

andod

dballstim

uliw

eres

omew

hatreduced;P

3aam

plitu

defro

mthe

distr

acterw

asredu

ced.Th

emeditatio

n-indu

cedredu

ctionin

P3aa

mplitu

dehadap

ositive

correlationwith

theq

ualityandexperie

nceo

fmeditatio

n

13JC

ognNeurosci.2009,

21(8):15361549.[36]

Health

ymeditators

andno

nmeditators

Thea

ttentionalblin

ktask

Two-grou

pstu

dyVipassana

Meditatio

n

Thetap

hase

lockingin

consciou

stargetp

erceptionandsuggestthatafterm

entaltrainingthe

cogn

itive

syste

mismorer

apidlyavailabletoprocessn

ewtargetinform

ation.Mentaltrainingwas

notassociatedwith

changesinthea

mplitu

deof

T2-in

ducedrespon

seso

roscillatoryactiv

itybeforetask

onset

14Neurorepo

rt.2007,18

(16):17091712.[39]

Health

ymeditators

andno

nmeditators

Them

ismatch

negativ

ity(M

MN)

paradigm

Two-grou

pstu

dySudarshankriyay

oga

meditatio

n

Meditatorswerefou

ndto

have

larger

MMNam

plitu

desthanno

nmeditators.Th

emeditatorsalso

exhibitedsig

nificantly

increasedMMNam

plitu

desimmediatelyafter

meditatio

nsuggestin

gtransie

ntsta

techangeso

wingto

meditatio

n.

15PL

oSBiol.2007,5(6):

e138.[35]

Health

ymeditators

andno

nmeditators

Thea

ttentionalblin

ktask

Two-grou

pstu

dyVipassana

Threem

onthso

fintensiv

ementaltrainingresultedin

asmallera

ttentionalblin

kandredu

ced

brain-resource

allocatio

nto

thefi

rsttarget,as

reflected

byas

mallerT

1-elicitedP3

b,a

brain-po

tentialind

exof

resource

allocatio

n.Th

oseind

ividualsthatshow

edthelargestdecrease

inbrain-resource

allocatio

nto

T1generally

show

edtheg

reatestreductio

nin

attentionalblin

ksiz

e.Th

eseo

bservatio

nsproviden

ovelsupp

ortfor

thev

iewthatthea

bilityto

accuratelyidentify

T2depend

supo

nthee

fficientd

eploym

ento

fresou

rces

toT1.Th

eresultsalso

demon

stratethat

mentaltrainingcanresultin

increasedcontroloverthe

distr

ibutionof

limitedbrainresources.

16IntJ

Neurosci.2006,116

(12):14191430.[43]

Health

yindividu

als

Auditory

oddb

all

task

with

twotones

(stand

ardandtarget)

One

grou

pwas

assessed

intwoseparate

cond

ition

s(selfas

control)

Cyclicm

editatio

nTh

erew

asredu

ctionin

thep

eaklatencieso

fP300after

cyclicm

editatio

natFz,C

z,andPz

comparedto

the

prevalues.Th

eP300peak

amplitu

desa

fterC

Mwereh

ighera

tFz,Cz

,and

Pzsites

comparedto

the

prevalues.

17Ch

inMed

SciJ.1999,4

(2):7579.[40]

Health

ymeditators

andno

nmeditators

Thea

udito

rymism

atch

negativ

ity(M

MN)and

P300

Two-grou

pstu

dyMusicalmeditatio

nMMNam

plitu

desinthetrained

child

renwerelargerthanthoseinthec

ontro

lgroup

.In

additio

n,theM

MNam

plitu

desw

ereidenticalin

attend

andigno

recond

ition

sfor

both

grou

ps.


evoked potentials changes occurred in brainstem evokedpotentials only in Qigong [15], not in transcendental medita-tion [14], in Sahaja yoga [17], or in OMmeditation [11].Withrespect to mid latency auditory evoked potentials assessed infour meditations changes were seen in all four meditations[5, 12, 15, 1719], that is, Qigong, Sahaja yoga, meditation onOM, and cyclic meditation. This suggests that meditationmodifies neural generators at the level of specific thalamicnuclei, thalamic radiation, and primary sensory corticesirrespective of the meditation techniques. Long latency AEPschanged in two out of the three meditations in which theywere recorded. Hence there were changes during Qigong andOM meditation but not during TM.

3.4.3. Visual Evoked Potentials. Visual evoked potentials wererecorded in a single study on Qigong meditators [16]. Therewas a significant increase in peak-to-peak amplitude ofN80-P115-N150 and N150-P200-N280 waves during Qigongmeditation. The authors suggest that N80-P115-N150-P200recorded may have corresponded to N70-P100-N130-P170reported by Vaughan in 1996 [30]. The first positive compo-nent is believed to be generated within thalamocortical radi-ations; the subsequent negative component is generated inlamina IV cb.The next positive component reflects inhibitoryactivity within this lamina and the later positive componentreflects extra striate cortex activity.This suggests that Qigongmeditation increases the activity in the visual pathway fromthalamocortical radiations up to the extra striate cortex withall the relay centers in between being included.

3.5. Results of ERPs. Healthy experienced Sahaja yoga med-itators and nonmeditators were assessed in a two-groupstudy using an affective picture viewing task [31]. In thiscomparison between long-term Sahaja yoga meditators andnonmeditators, mid latency ERPs were attenuated for bothpositive and negative pictures and a stronger ERP negativitybetween 200 and 300ms was found in meditators regardlessof picture valence.

There were two separate studies on healthy experiencedVipassana practitioners using an auditory oddball task [32,33]. In both the studies the groups were assessed in twoseparate conditions (the self as control design), that is,Vipassana meditation and random thinking. In one of thestudies Vipassana practitioners showed greater P3b ampli-tudes to the target tone after meditation than they did bothbefore meditation and after the nonmeditation session [32].The other study reported changes in multiple components inresponse to the standard and target stimuli; the meditation-induced reduction in P3a amplitude had a positive correlationwith the quality and experience of meditation [33].

In another study healthyVipassanameditators were givena three-stimulus auditory oddball task [34]. The group wasassessed in two separate conditions, that is, Vipassana medi-tation and instructedmind wandering.Meditation comparedto the control condition had decreased evoked delta power todistracter stimuli concomitantly with a greater event-relatedreduction of late (500900ms) alpha-1 (810Hz) activity,suggestive of a modification of attentional engagement todistracters. Additionally, standard stimuli were associated

with increased early event-related alpha phase synchrony(intertrial coherence) and evoked theta phase synchrony.Finally, during meditation, there was a greater differentialearly-evoked gamma power to the different stimuli. Correla-tion analysis indicated that this effect from ameditation state-related increase in early distracter-evoked gamma powerand phase synchrony was specific to longer-term expertpractitioners.

Two separate studies compared healthy Vipassana med-itators and nonmeditators using the attentional blink task[35, 36]. In one study three months of intensive mentaltraining resulted in a smaller attentional blink and reducedbrain-resource allocation to the first target, as reflected by asmaller T1-elicited P3b, a brain-potential index of resourceallocation [35]. This efficiency in brain resource allocationmight explain the findings of the other study which reportedchanges, especially in theta phase locking in conscious targetperception [36].

Healthy practitioners of Vipassana and loving kindnessmeditation and nonmeditators were assessed in an attentionblink task and an attention auditory task [37]. Hence this two-group study compared practitioners of Vipassana and lovingkindness meditation with nonmeditators. Three months ofintensive meditation training reduced variability in atten-tional processing of target tones and reduced reaction timevariability. Those individuals with greatest increase in neuralresponse consistency had largest decrease in behavioralresponse variability. Reduced variability in neural processingwas observed regardless of whether the deviant tone wasattended to or unattended. Meditation can significantly affectattention and brain function.

Performance in a Global-to-Local target task was com-pared between healthy open monitoring meditators andnonmeditators [38]. The study was conducted in two phases.Phase 1 was a cross sectional study. Phase 2 was a longitudinalstudy. Open monitoring meditation practitioners showed anenhanced processing of target level information, in contrastto the control group, which showed a local target selectioneffect only in the P1 and a global target selection effect inthe P3 component; meditators showed effects of local infor-mation processing in the two other components (other thanP3) and of global processing for two other components.Thus,meditators seem to display enhanced depth of processing. Inthe longitudinal experiment, meditationmodulated attentionafter a 4-day meditation retreat.

Two studies reported the effect of meditation on mis-match negativity (MMN) [39, 40] Healthy practitioners ofSudarshan Kriya yoga and nonmeditators were comparedusing the mismatch negativity (MMN) paradigm [39]. Inthis two-group, comparative study Sudarshan Kriya yogameditators were found to have larger MMN amplitudesthan nonmeditators. Meditators also exhibited significantlyincreased MMN amplitudes immediately after meditationsuggesting transient state changes owing to meditation. TheMMN is related to neuropsychological functioning, partic-ularly to executive functions [41]. Another study on healthycomparing children with training in musical meditation andnonmeditators using auditory mismatch negativity (MMN)and P300 [40] reported similar results.


Apart from the mismatch negativity (MMN) paradigmP300 can also be a useful indicator for neuropsychologicalfunctioning such as brain resource allocation for attentionalprocessing. Two separate studies on two different types ofmeditation supported the findings mention in the aboveparagraph [42, 43]. Healthy practitioners ofmeditativemind-fulness and a control groupwere assessed using a row/columnspeller task [42]. In this two-group study, the meditativemindfulness induction (MMI) and non-MMI control groupwere compared. MMI subjects were significantly more accu-rate than control subjects and they produced significantlylarger P300 amplitudes than control subjects at the vertex andparietooccipital region. In a separate study, practitioners of amoving meditation called cyclic meditation were assessed ontwo separate days, practicing cyclic meditation or an equalduration of supine rest for comparison [43]. On both daysthey were given an auditory oddball task with two tones(standard and target). There was a reduction in the peaklatency of P300 after cyclic meditation at the frontal region,vertex, and parietal region. Also the P300 peak amplitudesafter CM were higher at the same sites.

In addition to the studies on healthy participants theeffect of meditation was evaluated on patients with bipolardisorder which is characterized by a number of attentionalabnormalities. Patients with bipolar disorder and normalhealthy participants were assessed with a visual A-X con-tinuous performance task [44]. In this two-group study,mindfulness based cognitive therapy in bipolar disorderimproved attentional readiness and attenuated activationof nonrelevant information processing during attentionalprocesses.

Four separate studies compared meditators and non-meditators using different tasks for ERPs [4548]. In oneof the studies healthy meditators of various traditions andnonmeditators performed the Stroop task [45]. Meditatorsshowed greater executive control (i.e., fewer errors), a highererror related negativity, and emotional acceptance thancontrols. Another study used emotionally loaded stimuli(i.e., the International Affective Picture System) [46]. Theresult showed different emotional processing in meditationpractitioners. At high levels of processing meditators areless affected by stimuli with an adverse emotional load,while processing of positive stimuli remains unaltered. Inanother study healthy meditators from different traditionsand nonmeditators were assessed using anticipatory andpain-evoked ERPs [47]. Meditation was found to reducethe anticipation and negative appraisal of pain. Practitionersof imaginative meditators and nonmeditators were assessedduring hand movement(s) and the idle thinking state [48].Imagining moving the hand is associated with event-relateddesynchronization of the beta EEG.This occurredmore oftenand predictably in meditators compared to controls.

3.5.1. Summary of Event-Related Potential Studies. The resultsof the study on Sahaja yoga practitioners showed meditationcan enhance frontal top-down control over fast automaticsalience detection, based on amygdala functions followinglong-term meditation [31]. Studies on Vipassana meditators

showed increased attentional engagement after meditation,enhanced perceptual clarity, decreased automated reactivity,increased efficiency in distribution of limited brain resources,and switching attention [3237]. Similar findings werereported in studies done on open monitoring meditation,Sudarshan Kriya yoga, musical meditation, and meditativemindfulness and cyclic meditation [3843]. Meditators werealso reported to have greater emotional acceptance, wereless affected by stimuli with an adverse emotional load, andreduced the anticipation and negative appraisal of pain [4547]. Hence meditation can induce a mental state whichis characterized by efficient brain resource allocation withgreater emotional control.

4. Limitations of EP and ERP Studies Reviewed

One of the main limitations of the studies reviewed is in thestudy design. Out of the 11 EP studies there was just one [17]which randomized the participants to the three experimentalconditions. The other multiple-group studies [16, 1821] didnot use randomization. Three other early studies [1, 14, 15]had a single group which is an obvious disadvantage. Theremaining 4 studies assessed the meditators as their owncontrol on a separate day or days. In one out of four studiesthe assignment to meditation or the control interventionwas random [5], whereas in the other 3 studies [1113] thesequence was fixed and hence the effect of one interventionon another could not be ruled out. Also a disadvantage of theself-as-control design is that meditators with long experiencein meditation may get into a meditative state even duringthe nonmeditation control sessions. Apart from the disadvan-tages in study design another disadvantage especially in theearly studies [1, 1416] was small sample sizes (range between5 and 15). This is not seen in more recent studies [12, 13]( = 60 and = 48, resp.). On the whole evoked potentialsoffer poor spatial and temporal resolution compared to fMRIandMEG. Also the localization of changes is restricted to thesensory pathway activated by the specific stimulus. Despitethese limitations evoked potentials continue to be usefulto studies on practices like meditation as they are far lessdistracting and do not involve a drastic change in posture asis required for fMRI.

In the ERP studies reviewed the number of multiple-group studies (12 studies) was higher than the EP studiesreviewed in the present study. However the evidence of theERP studies is also with similar limitations as none of theERP studies used randomization as a method of allocatingthe participants to different groups.

5. Limitations of the Present Study

Thepresent study has several limitations: (i) the present studydid not review studies onmeditation and EEG, (ii) the studiesonmeditation and EPswere not homogenous, (iii) the studiesreviewed in the present study were not categorized accordingto the Jadad scale, and (iv) the studies included in the presentstudy were searched from only one database, that is, PubMed.


6. Directions for Future ResearchSuggested by This Study

The present study has shown that EPs are useful in localizingchanges in meditation to areas such as the brainstem, tha-lamus, thalamocortical radiations, primary sensory cortices,and association cortical areas and ERPs can provide usefulinformation about neurocognitive processing of attentionand brain resource allocation. Most of the studies are limitedby small sample sizes, lack of proper controls, no objectiveway of assessing the quality ofmeditation, and awide range ofvariation in the practitioners sampled. This can be correctedin future studies. Also studies can be specifically designedto verify whether the findings of EP studies which suggestthat changes occur in the thalamus, thalamocortical connec-tions, and primary relays and enhancement in attention andincreased efficiency of brain resource allocation as suggestedbyERP studies are indeed correct. To verify these resultsmorerigorous studies with a better design, larger sample size andstudies of EPs and ERPs in combination with neuroimagingduring meditation are recommended.

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper.

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