Time-dependent cortical asymmetries induced by emotional arousal

16 Pages·2002·0.49 MB·English

InternationalJournalofPsychophysiology44Ž2002.67(cid:1)82
Time-dependent cortical asymmetries induced by
emotional arousal: EEG analysis of event-related
synchronization and desynchronization in individually
defined frequency bands
(cid:1)
Ljubomir I. Aftanas , Anton A. Varlamov, Sergey V. Pavlov,
Viktor P. Makhnev, Natalya V. Reva
PsychophysiologyLaboratory,State-ResearchInstituteofPhysiology,SiberianBranch,RussianAcademyofMedical
Sciences,Timako(cid:1)astr.4,630117,No(cid:1)osibirsk,Russia
Received21March2001;receivedinrevisedform14August2001;accepted12September2001
Abstract
Event-related desynchronization ŽERD. and synchronization ŽERS. in the individually defined theta, alpha-1,
alpha-2 and alpha-3 frequency bands were measured in 20 healthy subjects in response to International Affective
PictureSystemŽIAPS.stimuliwithlow,moderateandhigharousalŽLA,MAandHA.content.The62-channelEEG,
skin conductance response ŽSCR. and heart rate ŽHR. were simultaneously recorded while subjects viewed
sequentially presentedpicturesandsubjectivelyratedthemaftereachpresentation.Inthetheta band,bothMAand
HAvs.LAstimuli induced larger synchronization overthe left anterior and bilaterally overposterior cortical leads.
However, rather unexpectedly, both MA and HA vs. LA stimuli yielded larger alpha-1 synchronization, predomi-
nantly overoccipital leads. In both theta and alpha-1 bands, affectively salient stimuli promptedlarger ERSagainst
the background of the overall dominance in power synchronization of posterior regions of the right hemisphere,
irrespectiveofstimuluscategory.Finally,inthealpha-3band,HAstimuliinducealateralizedtime-dependentpower
increase over anterior leads of the left hemisphere. The hemispheric asymmetries revealed point to recruitment of
notonlyposteriorregions ofthe right hemisphere Žtheta andalpha-1 bands.,but also ofanterior regions ofthe left
hemisphere Žtheta and alpha-3 bands. in affect analysis beyond valence dimension.In terms of affective chronome-
try, the significant arousal(cid:2)time interactions clearly indicate that in the theta frequency band discrimination of
affectivestimulihasalreadystartedat200mspost-stimulus,whereasinthealpha-1andalpha-3bandsthisprocessis
delayedby upto 800(cid:1)1200ms.(cid:1) 2002Elsevier Science B.V.All rights reserved.
Keywords: EEG; Emotion; Emotional arousal; Theta; Alpha; Event-related desynchronization and synchronization; Hemispheric
asymmetry;Skinconductance;Heartrate;Affectivechronometry
(cid:1)Correspondingauthor.Tel.:(cid:2)7-3832-334387;fax:(cid:2)7-3832-324254.
E-mailaddress:[email protected]ŽL.I.Aftanas..
0167-8760(cid:3)02(cid:3)$-seefrontmatter(cid:1)2002ElsevierScienceB.V.Allrightsreserved.
PII: S0167-8760Ž01.00194-5
68 L.I.Aftanasetal.(cid:3)InternationalJournalofPsychophysiology44(2002)67(cid:1)82
1. Introduction mation-processing, are enhanced. Third, cortical
activityisinvestigatedusingtheevent-related syn-
Along with valence Žpleasant(cid:3)unpleasant., chronization(cid:3)desynchronization ŽERD(cid:3)ERS.
arousal Žhigh(cid:3)low. dimension of emotion experi- method ŽPfurtscheller and Aranibar, 1977.. Sen-
ence has consistently emerged from multidimen- sory, cognitive and motor processing can result in
sional scaling and factor-analytical studies of changes in the ongoing EEG in the form of
self-reported emotion Že.g. Russel and Bullock, event-related desynchronization ŽERD. or syn-
1985; Watson and Tellegen, 1985.. Contemporary chronization ŽERS.. Both phenomena are time-
research on cortical correlates of emotion func- locked to the event and highly frequency band-
tion have started totake into account this distinc- specific. Traditionally, ERD is interpreted as a
tion Že.g. Lang et al., 1998; Muller et al., 1999; correlate of an activated cortical area with in-
Aftanas et al., 2001; Junghofer et al., 2001.. Due creased excitability and the ERSin the alpha and
to ambiguity of the arousal concept, repeatedly lower beta bands can be interpreted, at least
discussedinthepsychophysiologicalliteratureŽfor under certain circumstances, as a correlate of a
review see Venables, 1984; Heller et al., 1997., deactivated cortical area. Spatial mapping of
the arousal dimension of emotion function has ERD(cid:3)ERS can be used to study the dynamics of
received little attention in EEG investigations. cortical activation patterns ŽPfurtscheller and
Consistent with the hypothesis that posterior re- LopesdaSilva,1999..Fewpreviousstudiesonthe
gions of the right hemisphere are involved in the ERD(cid:3)ERS responses to emotion-related stimuli
modulation of emotion-related arousal ŽHeller, haveexaminedthe narrowfrequency bandsofthe
1993., scarce EEG ŽNitschke et al., 1999; David- EEG and revealed that this EEG quantification
son et al., 2000a., ERPs ŽJunghofer et al., 2001., method can uncover the cortical correlates of
autonomousŽe.g.Heilman et al.,1978.,neuropsy- relatively small differences in emotion processing
chologicalŽHeller et al.,1997.andfMRIŽLang et ŽAftanas et al., 1996a,b,2001; Krause et al., 2000.
al., 1998. findings suggest this association. How- and personality ŽAftanas et al., 1996b., as well as
ever, it is yet undetermined how cortical EEG a dissociation between the neural correlates of
asymmetries, emerging during affective process- the processing of different types of emotional
ing, vary with the judged arousal of affectively stimuli ŽAftanas et al., 1996a,b, 2001; Krause et
salient stimuli. It is also unclear when, where and al., 2000.. However, since fixed frequency bands
at which frequencies it occurs. blur specific relationships between cognitive per-
The experimental paradigm used in our prior formanceandpowermeasurements,narrowtheta,
study ŽAftanas et al., 2001. was a good starting alpha-1, alpha-2 and alpha-3 frequency bands are
point for investigating howregional cortical activ- individually defined in relation to the individual
ityvaries asafunction ofarousal,EEGfrequency alpha frequency ŽDoppelmayr et al., 1998a..
and time course of affective responses. This Fourth, the use of a high-resolution 62-electrode
paradigm controls for several potentially con- recording montage provides more adequate to-
founding variables. First, IAPS stimuli ŽLang et pography of regional hemispheric activation pat-
al., 1999. enable control for valence and arousal terns during emotional processing. Fifth, the si-
dimensions. Stimuli are presented for 6 s. This multaneously recorded SCR and electrocardio-
standard time recommendedforself-report rating gram ŽECG. data give important support to the
of IAPS stimuli ŽBradley and Lang, 1994. is ac- proposal that picture differences are attributable
ceptable for detecting both early Ževaluative. and to emotional arousal.
later Žexperiencing. aspects of affective process- Thepresent experiment,based onthe merits of
inginEEGinvestigations Že.g.Mulleretal.,1999; both the ERD(cid:3)ERS method and IAPS stimuli
Aftanas et al., 2001.. Second, participants are set, was undertaken to examine whether arousal
instructed to attend to the pictures, but no overt dimension of an emotion function would be asso-
response is required, so inherent affective reac- ciated with ERD(cid:3)ERS measures of interhemi-
tions to these stimuli, rather than cognitive infor- spheric asymmetries in the anterior(cid:1)posterior di-
L.I.Aftanasetal.(cid:3)InternationalJournalofPsychophysiology44(2002)67(cid:1)82 69
rection of the cortical plane. We contrasted Doppelmayr et al., 1998b; Sakowitz et al., 2000;
changes in brain activity induced by IAPS pic- Aftanas et al., 2001; Aftanas and Golocheikine,
tures segregated into low, moderate and high 2001; Basar et al., 2001.. The prediction was that
arousal categories. We raised the following ques- cortical influences of arousal would be predomi-
tions: dointerhemispheric asymmetries, emerging nantly associated with the theta and the lowest
during affective processing and indexed by alpha bands, indexing involvement of orienting,
ERD(cid:3)ERS measures, vary with the judged stimulus decoding and memory Žtheta., as well as
arousal of an affective picture foreground? If so, alertness(cid:3)vigilance Žlowest alpha. mechanisms in
when, where and at which frequencies does this affective processing. In terms of affective
occur? chronometry ŽDavidson, 1998., according to our
Several predictions were made. In line with recent pilotstudyŽAftanasetal.,2001.amongthe
Heller’s model ŽHeller, 1993; Heller et al., 1997., four frequency bands, the theta band was as-
as well as with our pilot ERD(cid:3)ERS study with sumed to be the fastest in detecting affective
IAPS pictures ŽAftanas et al., 2001., we predicted salience of incoming stimuli.
that modulatory influences of emotional arousal
would be restricted to posterior cortical regions,
with the strongest impact of high arousal stimuli 2. Method
on right posterior activity. The modulatory influ-
ences of emotional arousal on anterior brain ac- 2.1. Subjects
tivity were difficult to anticipate. According to
existing models of emotion, anterior cortical re- Subjects ŽSs, n(cid:4)20. were right-handed college
gions are uniquely involvedin the valence dimen- students Ž13 males, 7 females. between the ages
sion of emotion, with pleasant affect associated of 18 and 26 years. All the Ss signed an informed
with greater left activity and unpleasant affect consent to participate in a study and the research
associatedwithgreaterrightactivityŽHeller,1993; received prior approval of the institutional ethics
Davidson et al., 2000a,b.. The greater right than committee. All the Ss had normal or corrected-
left anterior activity associated with unpleasant to-normal vision. The day before the investiga-
valence would probably serve to cancel the in- tion, the Ss were reminded to refrain from exer-
crease in left anterior activity expected for posi- cise and consumption of alcohol during this day.
tive stimuli. Prediction in the frequency domain Allthe Sswerepaidforparticipationinthe study.
was related to findings that theta and alpha oscil-
lations defined in narrow frequency bands are 2.2. Stimuli (IAPS)
regarded as reflecting activity of multifunctional
neuronal networks, differentially associated with The IAPS pictures as scanned color images
sensory, cognitive and affective processing Žfor a ŽCSEA-NIMH, 1999. were selected by normative
review see Crawford et al., 1996; Aftanas et al., arousal ŽARO. and valence ŽVAL. ratings ŽLang
1998; Klimesch, 1999; Basar et al., 1999, 2001.. et al., 1999. and arranged into five subsets Žeight
Desynchronization in the lower and medium al- stimuli per category.: Ž1. emotionally neutral (cid:2)
pha bands is associated with processes ofexternal low arousal pictures ŽNeutLA: ARO(cid:5)3.11; VAL
attention, such as alertness(cid:3)vigilance Žlowest al- (cid:6)4.87 and (cid:5)5.74.; Ž2. emotionally positive (cid:2)
pha. and expectancy Žmedium alpha., whereas moderate arousal pictures ŽPosMA: ARO(cid:6)3.37
desynchronized upper alpha reflects enhanced and (cid:5)4.39; VAL(cid:6)6.35 and (cid:5)7.85.; Ž3. emotio-
cognitive processing Že.g. Klimesch et al., 1998a.. nally negative (cid:2) moderate arousal pictures
In turn, previous research suggests that higher ŽNegMA: ARO(cid:6)3.89 and (cid:5)4.67; VAL(cid:6)2.65
theta activity is best interpreted as an electro- and (cid:5)4.15.; Ž4. emotionally positive (cid:2) high
physiological manifestation of higher activation, arousalpicturesŽPosHA:ARO(cid:6)3.57and (cid:5)5.39;
related to orienting, attention, memory, affective VAL(cid:6)6.41 and (cid:5)7.89.; and Ž5. emotionally
and cognitive processing ŽKlimesch et al., 1996; negative (cid:2) high arousal pictures ŽNegHA: ARO
70 L.I.Aftanasetal.(cid:3)InternationalJournalofPsychophysiology44(2002)67(cid:1)82
(cid:6)5.04and (cid:5)5.72;VAL(cid:6)1.87and (cid:5)2.50.1.Re-
sulting arousal and valence ratings of the subsets
constructed are basically in line with earlier de-
monstrations for IAPS stimuli and exhibit a
quadratic relationship between valence and
arousal dimensions; pictures receiving higher
arousal ratings also reveal extreme Žeither posi-
tive or negative. valence ratings ŽLang et al.,
1993; Lang, 1995..
2.3. Electrophysiologicalrecording
2.3.1. Electroencephalogram
SCAN 4.1.1 software, a 128-channel electrical
signalimagingsystemŽESI-128,NeuroScanLabs.,
a modified 64-channel QuikCap with embedded
Ag(cid:3)AgClelectrodesŽNeuroSoftInc.andElectro-
Cap Gel ŽWeaver and Co. were used to record
EEGs from62 active scalp sites referenced to the
tipofthe nose Žsee Fig.1for the caplayout..The
Fig. 1. The electrocap layout and 12 regional means Žsix for
ground electrode was attached to the center of
eachhemisphere.usedforanalysesŽseetextfordetails..
the forehead. The impedance was kept below 5
k(cid:3). The EOGs were measured to control for
ocular artifacts using the QuikCap electrodes. fingers of both the left and right hands using
Vertical EOG was measured with electrodes Sensormedics Ag(cid:3)AgCl electrodes. Ten20 gel
placed 2 cm above and below the middle of right ŽWeaver & Co. was used as an electrolyte. The
eye. Horizontal EOG electrodes were placed as left and right signals were acquired with two
close as possible to the left and right outer canthi Coulbourn S71-22 skin conductance couplers,
ofthe eyes.Calibration wascarried outat 100 (cid:4)V which provided a constant 0.5 V across the elec-
at 10 Hz. The EEG and EOG signals were digi- trodes.Thecouplerswerecalibrated priortoeach
tally filtered at 0.3(cid:1)50 Hz Ž(cid:7)6-dB gain, (cid:6)(cid:7)12- session. The calibration values were used off-line
dB(cid:3)octave slope. and amplified Žgain 1000, reso- to convert the digitized raw signals to skin con-
lution 0.084 (cid:4)V(cid:3)bit, range 5.5 mV. via SynAmps ductance values in (cid:4)S. SCR data were fed into
amplifiers, sampled at 500 Hz and stored for high-voltage inputs of the third SynAmps of the
off-line analyses. ESI-128.
2.3.2. Skin conductanceresponse (SCR)
After an appropriate cleaning procedure with 2.3.3. Electrocardiogram(ECG)
OmniPrep abrasive ŽWeaver & Co., skin conduc- ECGs were recorded using the third SynAmps
tance electrodes were attached onto the palmar of the ESI-128, Ag(cid:3)AgClelectrodes and pre-cor-
sideofthe secondphalanx ofthe third andfourth dial bipolar lead, as recommended by Mulder
Ž1992..
All peripheral activities were digitized at 500
1The following pictures formed five categories: NeutLA: Hz throughout the entire 12-s trial period.2
7002, 7004, 7006, 7009, 7010, 7020, 7150 and 7175; PosMA:
2010, 2345, 2501, 2530, 2540, 5200, 5760 and 5780; NegMA:
1930, 2205, 3300, 9008, 9340, 9421, 9911 and 9920; PosHA:
1440, 1460, 1722, 1920, 4658, 4659, 4660 and 4669; NegHA: 2Fortechnicalreasons,high-qualityphysiologicalresponses
2800,3080,3150,3170,3261,9040,9405and9410. ŽbothSCRandECG.wereretainedonlyin13recordedSs.
L.I.Aftanasetal.(cid:3)InternationalJournalofPsychophysiology44(2002)67(cid:1)82 71
2.4. Procedure or movement-related artifacts. Only valid trials
were retained for analyses. There were no sig-
nificant differences in the number of valid trials
Ss were seated in a comfortable armchair and
per category ŽNeutLA: M(cid:4)12.85, S.D.(cid:4)2.01,
the light in the room was dimmed. The experi-
ment began with four 60-s eyes open(cid:3)eyes closed min.(cid:4)10;PosMA: M(cid:4)12.80,S.D.(cid:4)2.39,min.(cid:4)
9; NegMA: M(cid:4)12.75, S.D.(cid:4)1.88, min.(cid:4)8;
baselines that will not be reported here. A single
PosHA: M(cid:4)12.15, S.D.(cid:4)2.20, min.(cid:4)8; and
experimental trial had the following sequence: a
NegHA: M(cid:4)11.90, S.D.(cid:4)2.42, min.(cid:4)8..
blank screen was replaced by a small cross pre-
Changes in band power were defined as the
sented in the center of the screen for 4 s, and
percentage of decrease ŽERD. or increase ŽERS.
followed by presentation of a picture for 6 s. The
total length of EEG epoch recorded was 12 s Ž5 s in band power during the test interval Žhere 6000
before and 7 s after picture onset.. After the ms post-stimulus. as compared to the reference
interval Žhere (cid:7)3000to(cid:7)1000msbefore picture
picture offset, three affective dimensions of plea-
sure,arousalanddominanceŽinanine-pointscale onset. ŽPfurtscheller and Aranibar, 1977.. Fre-
for each dimension. were assessed using comput- quency bands were individually defined in rela-
erized Self-Assessment Manikin ŽSAM. ŽBradley tiontotheindividualalphafrequencyŽIAF.,which
and Lang, 1994.. Upon the completion of SAM was used as the cut-off point for the lower and
ratings, the stimulation program started the next upper alpha band. The bandwidth was also indi-
trial with a randomly determined interval of 1(cid:1)3 vidually determined and was calculated as the
s. In the preceding training procedure, Ss were percentage Ž20%. of IAF ŽDoppelmayr et al.,
confronted with six examples including neutral 1998a.. The frequency bands obtained by this
and affective stimuli that were not a part of the method are termed: theta, ŽIAF(cid:2)0.4.(cid:1)ŽIAF(cid:2)
main experimental set. In this training procedure, 0.6.; alpha-1, ŽIAF(cid:2)0.6.(cid:1)ŽIAF(cid:2)0.8.; alpha-2,
Ss learned to maintain gaze on the center of the ŽIAF(cid:2)0.8.(cid:1)ŽIAF(cid:2)1.0.; and alpha-3, ŽIAF(cid:2)
screen avoiding explorative eye movements, as 1.0.(cid:1)ŽIAF(cid:2)1.2.. Averaged over the entire sam-
well as to respond to SAM scales. Overall, there ple of 20 subjects, the IAF was 10.44 Hz and the
were 80 experimental trials. Each stimulus was following cut-off points were obtained: theta,
exposed twice in a block-randomizedfashion, dis- 4.10(cid:1)6.21;alpha-1,6.21(cid:1)8.28;alpha-2,8.28(cid:1)10.35;
tributed over two blocks of 40 trials. Because the and alpha-3, 10.35(cid:1)12.46 Hz. For each subject,
affective feature of a particular stimulus was not after band-pass filtering Ž96 dB(cid:3)octave roll-off,
necessarily in the center of the picture, stimuli warm-upfilter left, trim left and right of1000ms.
were mirrored for a second block of presenta- ERD(cid:3)ERSwascalculatedwithinthesebandswith
tions. In both blocks, the order of stimuli was a time resolution of 100 ms ŽPfurtscheller and
pseudo-randomized under the restriction that Aranibar, 1977; Doppelmayr et al., 1998a. and
trains of three pictures belonging to the same averaged according to the five categories.
subset should not occur. There was a break of 5
min between two blocks of presentations.
2.5.2. ERD(cid:3)ERS data reduction
With respect to spatial sampling points, elec-
2.5. Data analysis
trodes were collapsed into 12 electrode clusters
ŽFig. 1.. This procedure resulted in six regional
2.5.1. EEG analysis means for each hemisphere: anterior temporal
Contributions from the horizontal and vertical ŽAT.; frontal ŽF.; central ŽC.; parietotemporal
EOGs to the EEG were eliminated off-line by ŽPT.; parietal ŽP.; and occipital ŽO.. The average
submittingthedatatotheSCAN4.1eyemovement ERD(cid:3)ERSvalues across the respective electrode
correction algorithm ŽSemlitsch et al., 1986.. In sites were calculated for these regional means for
addition, individual EEG traces were visually in- each time interval of 100 ms and each arousal
spected for any remaining eye movement, EMG, category.
72 L.I.Aftanasetal.(cid:3)InternationalJournalofPsychophysiology44(2002)67(cid:1)82
2.6. Skin conductanceresponse the moderate arousal category ŽMA., whereas
data on high-arousal positive and negative stimuli
The skin conductance signals were downsam- were averaged into the high arousal category
pled to 10 samples(cid:3)s for analyses. For stimulus ŽHA.. As a result, three stimulus categories Žlow,
presentation periods, skin conductance responses moderate and high arousal pictures. were ob-
from the left hand were scored as responses oc- tained instead of five.3 The SAM, SCR and HR
curring between 0.9 and 5 s after picture onset data were treated in the same manner.
and exceeding 0.01 (cid:4)S Že.g. Prokasy and Raskin, Separateone-wayrepeated-measures ANOVAs
1973.. Log-transformation Žlog(cid:8)SCR(cid:2)1(cid:9). was ŽARO 3: low, moderate and high arousal. were
used to normalize the amplitude data. performed for individual SAM ratings, SCR
Žprobability and amplitude. and HR deceleration
2.7. Heart rate (HR) data. For each EEG frequency band, ERS(cid:3)ERD
data were analyzed in four-way repeated-mea-
The electrocardiogram ŽECG. output channel suresANOVAswiththefollowingfactors:arousal
was converted into HR(cid:3)0.5s. For the 6-s viewing ŽARO 3: low, moderate, high.(cid:2)hemisphere
period, mean values of HR(cid:3)0.5 s were used to ŽHEM2:left,right.(cid:2)localizationŽLOC6:AT,F,
construct a mean change score waveform Žmean C,PT,P and O.(cid:2)time ŽTIME 6: 1, 2, 3, 4, 5 and
HR(cid:3)0.5 s post-stimulus minus mean HR for the 6 s post-stimulus.. Additionally applied ANOVAs
last 0.5-s pre-stimulus. for editing and detection
ofacceleratoryanddeceleratorypeaksandnadirs,
respectively. The largest deceleratory values were 3As is evident fromthe above,three levels of arousal and
selected ŽRoedema and Simons, 1999.. emotionalitywerenotorthogonallycombined.Instead,neutral
stimuli were used for low arousal category, whereas both
2.8. Statistical analyses positiveandnegativepictureswereusedtoformmedium-and
high-arousal categories. Orthogonality was sacrificed for two
reasons. Due to existing quadratic relationships between va-
Before statistical analyses in order to obtain
lence and arousal, extremely high arousal values involve ex-
ERD(cid:3)ERS values of moderate and high emotio- tremevalencescores,andviceversaŽBradleyandLang,1994..
nal arousal, prompted by equal amounts of posi- In this respect, the psychophysiological meaning of positive
tive and negative stimuli, the following transfor- andnegativeemotionalityoflowarousalstimuliseemsrather
mations were performed. ERD(cid:3)ERS data on confusing. Another reason was related to the experimental
set-up.Additionallow-arousalstimuliwouldextendtheexper-
positive and negative pictures with moderate
imental procedurein time,thereby enhancing risks for inter-
arousal Žsee Section 2.2. were averaged to form feringinfluences offatigue.
Fig. 2. Ža. SAM ratings: Žb. SCR amplitude; Žc. SCR probability; and Žd. heart rate deceleration in beats(cid:3)min as a function of
arousal.
L.I.Aftanasetal.(cid:3)InternationalJournalofPsychophysiology44(2002)67(cid:1)82 73
depended on the time course and topography of indicating a greater extent of ERS over the right
effects revealed involving the arousal factor Žsee hemisphere overall ŽTable 1.. The highly signifi-
Section 3.. cant effect of the arousal factor shows higher
For all the analyses, degrees of freedom were theta production in response to both moderate
Greenhouse(cid:1)Geisser-corrected where appropri- ŽM(cid:4)(cid:7)30.99.andhighŽM(cid:4)(cid:7)36.28.whencom-
ate. All the post hoc comparisons were evaluated pared to low ŽM(cid:4)(cid:7)18.32. arousal stimuli over-
by means of the Scheffe test. all ŽTable 1.. As may be inferred from the sig-
nificantinteractionARO(cid:2)LOCpresentedinFig.
3a, all stimuli yielded topographically larger ERS
3. Results values over posterior than anterior sites and this
effect was more pronounced for the pictures with
3.1. SAM ratings
elevated arousal content. According to post hoc
comparisons, when compared to the LA, HA sti-
The mean arousal ratings for all the subcate-
muli produced significantly larger ERS over pari-
gories are presented in Fig. 2a. Pictures varied
robustly in arousal level (cid:8)FŽ2,44.(cid:4)60.85, P(cid:3) etotemporal, parietal and occipital loci, whereas
(cid:9) MA pictures prompted larger ERS only over oc-
0.000, which was rated significantly higher for
moderateŽM(cid:4)3.92.andhighŽM(cid:4)5.03.ascom- cipital leads Žpost hoc at P(cid:3)0.01.. As supported
pared to low ŽM(cid:4)2.50. arousal pictures. In turn, by significant interactions for ARO(cid:2)HEM(cid:2)
LOC and ARO(cid:2)LOC(cid:2)TIME ŽTable 1., the
higharousalstimuliwereratedsignificantlyhigher
than moderate arousal pictures Žall post hoc at theta band also revealed effects of arousal dis-
P(cid:3)0.01.. crimination, associated with the time factor and
hemispheric asymmetries in the anterior(cid:1)post-
3.2. Skin conductance erior direction of the cortical plane. In an effort
to substantiate the essence of these effects, the
As expected, skin conductance activity was additional four-way repeated-measures ANOVA
higher in the response to affectively salient vs. including the anterior and posterior regions as a
neutral stimuli ŽFig. 2b,c.. This is demonstrated caudality factor was performed: arousal ŽARO 3:
by significant effects of the ARO factor for SCR LA,MA,HA.(cid:2)caudality ŽCAUD2: AT,F,C vs.
amplitude and probability (cid:8)FŽ2,24.(cid:4)10.65, P(cid:3) PT, P, O.(cid:2)hemisphere ŽHEM 2: left, right.(cid:2)
0.007 and FŽ2,24.(cid:4)15.69, P(cid:3)0.000, respec- time ŽTIME 6: 1, 2, 3, 4, 5 and 6 s post-stimulus..
(cid:9)
tively. Both skin conductance amplitude and Because the resulting two-way interaction of
probability values were larger for HA vs. LA ARO(cid:2)CAUD (cid:8)FŽ2,38.(cid:4)9.53; P(cid:3)0.001(cid:9) is in-
stimuli. Furthermore, HA when comparedto MA cluded in the three-way interaction ARO(cid:2)
stimuli prompted higher SCR probability ŽFig. CAUD(cid:2)HEM (cid:8)FŽ2,38.(cid:4)4.53; P(cid:3)0.024(cid:9), only
2b,c. Žall post hoc at P(cid:3)0.01.. this higher-order interaction is plotted in Fig. 4a.
Analysis of this interaction clearly demonstrates
3.3. Heart rate
that over the left anterior regions, both MA and
HA stimuli induce larger ERS than LA pictures.
As Fig. 2d illustrates, there was a significant
main effect of arousal (cid:8)ARO: FŽ2.24.(cid:4)8.45, P(cid:3) This is supported by the significant interaction
(cid:9) ARO(cid:2)HEM (cid:8)FŽ2,38.(cid:4)4.96; P(cid:3)0.016(cid:9) in sepa-
0.006, indicating the largest deceleratory activity
rate ANOVA for anterior leads and post hoc
for HA, intermediate for MA and the lowest for
LA stimuli Žpost hoc at P(cid:3)0.01.. comparisonsat P(cid:3)0.01.Inturn,theta powerwas
significantly larger on right vs. left hemisphere
(cid:8)
3.4. ERD(cid:3)ERS measures anteriorelectrodesonlyfortheLAstimuli HEM:
FŽ1,19.(cid:4)8.26; P(cid:3)0.010(cid:9) and there were no
3.4.1. Theta band hemispheric asymmetries for MA and HA stimuli
ANOVAfor the whole test interval and all the ŽFig.4a,left panel..Separate ANOVAsforposte-
loci resulted in the robust effect of hemisphere, rior leads exhibit robust overall effects of greater
74 L.I.Aftanasetal.(cid:3)InternationalJournalofPsychophysiology44(2002)67(cid:1)82
Table1
ANOVA(cid:8)AROŽ3.(cid:2)HEMŽ2.(cid:2)LOCŽ6.(cid:2)TIMEŽ6.(cid:9)resultsŽF,d.f.andprobability.ofmaineffects,alongwithtwo-andthree-way
interactions fortheta,alpha-1,alpha-2,andalpha-3bands
Effect d.f. Theta Alpha-1 Alpha-2 Alpha-3
ARO 2,38 12.11 4.23 NS NS
P(cid:3)0.000 P(cid:3)0.027
HEM 1,19 12.91 6.94 NS NS
P(cid:3)0.002 P(cid:3)0.016
LOC 5,95 21.61 15.94 3.59 44.23
P(cid:3)0.000 P(cid:3)0.000 P(cid:3)0.041 P(cid:3)0.000
TIME 5,95 103.57 33.21 5.25 7.04
P(cid:3)0.000 P(cid:3)0.000 P(cid:3)0.019 P(cid:3)0.005
ARO(cid:2)HEM 2,38 NS NS NS 3.34
P(cid:3)0.046
ARO(cid:2)LOC 10,190 6.92 7.26 4.45 2.35
P(cid:3)0.000 P(cid:3)0.000 P(cid:3)0.000 P(cid:3)0.030
ARO(cid:2)TIME 10,190 2.54 NS NS 2.77
P(cid:3)0.024 P(cid:3)0.018
ARO(cid:2)HEM(cid:2)LOC 10,190 3.11 NS NS NS
P(cid:3)0.029
ARO(cid:2)LOC(cid:2)TIME 50,950 2.04 NS NS NS
P(cid:3)0.035
ARO, arousal; HEM, hemisphere; LOC, localization ŽAT, F, C, PT, P, O.; TIME Ž6 by 1000 ms after stimulus onset.. Only
significanttwo-andthree-wayinteractions associatedwiththearousalfactorarereported.
ERS over the right hemisphere (cid:8)overall HEM in duce larger ERS in the 200(cid:1)700-ms time window
separate ANOVA: FŽ1,19.(cid:4)14.82; P(cid:3)0.001(cid:9) post-stimulus, whereas MA vs. LA pictures are
and demonstrate that affectively salient vs. neu- discriminated somewhat later and in the shorter
tral stimuli bilaterally induce significantly larger time periodof300(cid:1)500msŽposthocat P(cid:3)0.01..
theta power Žall post hoc at P(cid:3)0.01; Fig. 4a, All the other interactions involving arousal factor
right panel.. Finally, the significant interaction were not or only marginally significant.
ARO(cid:2)CAUD(cid:2)TIME (cid:8)FŽ10,190.(cid:4)2.33; P(cid:3)
(cid:9)
0.034 further indicates that all affective vs. low
3.4.2. Alpha-1 frequency band
arousal pictures induce a greater amount of the
The significant main effect of hemisphere
theta ERS over posterior regions in the early
ŽTable 1. revealed overall greater alpha synchro-
post-stimulus period of 1 s, whereas high arousal
nization over the right hemisphere. The main
stimuli reveal the second power increase at 4 s
effect of the arousal factor, along with respective
post-stimulus ŽFig. 4b, right panel, post hoc at
means, indicates the largest extent of synchro-
P(cid:3)0.01.. nization for the moderate ŽM(cid:4)(cid:7)14.47., inter-
For a better understanding of the early tem- mediate for high ŽM(cid:4)(cid:7)12.01., and faint power
poraleffects ofarousal overposteriorleads,sepa- increase in response to the low arousal ŽM(cid:4)
rate repeated-measures ANOVAs for PT, P, and (cid:7)3.06. stimuli overall. The two-way interaction
O regions with higher time resolution were per- ARO(cid:2)LOC ŽTable 1, Fig. 3b. further clarifies
formed(cid:8)AROŽ3.(cid:2)HEMŽ2.(cid:2)LOCŽ3.(cid:2)TIMEŽ7: that whencomparedtothe LA,bothMAandHA
100, 200, 300, 400, 500, 600 and 700 ms post- stimuli prompted greater ERS only over occipital
stimulus.(cid:9). The emerging significant interaction leads Žpost hoc at P(cid:3)0.01.. Finally, additional
ARO(cid:2)TIME (cid:8)FŽ12,228.(cid:4)3.52; P(cid:3)0.013(cid:9) de- ANOVA for occipital leads at the early post-
monstrated ŽFig. 5a. that HA vs. LA stimuli pro- stimulus phase (cid:8)AROŽ3.(cid:2)HEMŽ2.(cid:2)TIMEŽ6:
L.I.Aftanasetal.(cid:3)InternationalJournalofPsychophysiology44(2002)67(cid:1)82 75
Fig. 3. Two-way arousal(cid:2)localization interactions in: Ža. theta; Žb. alpha-1; Žc. alpha-2 and Žd. alpha-3 bands for all the three
picturecategoriesinthe6-stestintervalŽERSgoesdown,ERDgoesup..
200, 400, 600, 800, 1000 and 1200 ms post-stimu- duce greater ERD over parietal sites ŽTable 1,
lus.(cid:9) resulted in the significant interaction ARO Fig. 3c.. The more pronounced effect of affective
(cid:2)TIME (cid:8)FŽ10,190.(cid:4)2.95; P(cid:3)0.027, Fig. 5b., stimuli over posterior leads is also supported by
according to which MA vs. LA pictures induce significanteffects ofLOCforbothHA(cid:8)FŽ5.95.(cid:4)
greater ERS starting at 400(cid:1)600 ms post-stimu- 5.80; P(cid:3)0.000(cid:9) and MA (cid:8)FŽ5.95.(cid:4)4.36; P(cid:3)
(cid:9)
lus. The emerging difference reaches significance 0.001, along with an insignificant effect for LA
at 1200 ms Žpost hoc at P(cid:3)0.01.. During this (cid:8)FŽ5.95.(cid:4)1.47; P(cid:3)0.205(cid:9) stimuli in separate
period,theHApicturesyieldedintermediateERS ANOVAsfor each category.
values.
3.4.4. Alpha-3 band
3.4.3. Alpha-2 band According to preliminary analyses, overall in
Although in the alpha-2 band ERD(cid:3)ERS val- the alpha-3 frequency band, anterior temporal,
ues exhibited great inter-individual variability, frontal and central regions exhibited short-lasting
particularly over anterior leads, inspection of re- significant synchronization within the first 1200
spective means ofthe only significant effect, asso- ms post-stimulus, whereas posterior loci exhibited
ciated with the arousal factor Ži.e. two-way inter- significant desynchronizationthat started onaver-
action ARO(cid:2)LOC. indicates that HA vs. both age from 200 to 400 ms post-stimulus and per-
MA and LA stimuli exhibited tendencies to in- sisted throughout the whole test interval of
76 L.I.Aftanasetal.(cid:3)InternationalJournalofPsychophysiology44(2002)67(cid:1)82
Fig. 4. Ža. Three-way arousal(cid:2)caudality(cid:2)hemisphere and Žb. arousal(cid:2)caudality(cid:2)time interactions in theta band for all the
threepicturecategoriesinthe6-stestinterval;L,left,andR,right,hemisphere.
0(cid:1)6000ms.Forthewholetestinterval,thearousal period and anterior leads (cid:8)AROŽ3.(cid:2)HEMŽ2.(cid:2)
factor was involved in the only interaction ARO LOCŽ3: AT, F and C.(cid:2)TIMEŽ6: 200, 400, 600,
(cid:2)LOCŽTable1.,presented in Fig.3d.According 800, 1000 and 1200 ms post-stimulus.(cid:9) revealed a
to this interaction, HA vs. LA stimuli induced significant interaction for ARO (cid:2) TIME
larger ERS over anterior leads whereas over pos- (cid:8)FŽ10,190.(cid:4)2.81; P(cid:3)0.013(cid:9) embedded in the
terior sites all the three picture categories three-way interaction ARO(cid:2)HEM(cid:2)TIME
prompted about equal extent of desynchroniza- (cid:8)FŽ10,190.(cid:4)2.91; P(cid:3)0.021(cid:9) ŽFig. 6.. Inspection
tion. The additional ANOVA for the early test of respective means of the last interaction indi-
Fig.5. Ža.Two-wayarousal(cid:2)timeinteractions forparietal,parietotemporalandoccipitalleadsintheta andŽb.occipitalleadsin
alpha-1bandsasafunctionofarousal.