Psychiatry Research: Neuroimaging 173 (2009) 100–106

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Psychiatry Research: Neuroimaging

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Brain responses to repeated visual experience among low and high sensation seekers:Role of boredom susceptibility

Yang Jianga,⁎, Joann Lianekhammya, Adam Lawsona,1, Chunyan Guob, Donald Lynamc, Jane E. Josephd,Brian T. Goldd, Thomas H. Kellya

aDepartment of Behavioral Science, University of Kentucky Chandler Medical Center, University of Kentucky, Lexington, KY, USAbDepartment of Psychology, Capital Normal University, Beijing, ChinacDepartment of Psychological Sciences, Purdue University, West Lafayette, IN, USAdDepartment of Anatomy & Neurobiology, University of Kentucky Chandler Medical Center, University of Kentucky, Lexington, KY, USA

⁎ Corresponding author. Department of Behavioral SCollege of Medicine, Lexington, KY, 40536, USA. Tel.: +15350.

E-mail address: yjiang@uky.edu (Y. Jiang).1 Current address: Department of Psychology, Eastern K

KY , USA.

0925-4927/$ – see front matter © 2008 Elsevier Irelandoi:10.1016/j.pscychresns.2008.09.012

a b s t r a c t

a r t i c l e i n f o

Article history:

To better understand indiv Received 21 January 2008Received in revised form 18 June 2008Accepted 24 September 2008

Keywords:Sensation seekingRepetition effectEEG/ERPPrimingLORETALPC

idual differences in sensation seeking and its components, including boredomsusceptibility and experience seeking, we examined brain responses of high and low sensation seekersduring repeated visual experience. Individuals scoring in the top and bottom quartiles from a college-agedpopulation on the Brief Sensation-Seeking Scale (BSSS) participated in an event-related potentials (ERPs)experiment. Line drawings of common objects were randomly intermixed and presented 1–3 times. Sixty-four channel ERP responses were recorded while participants classified items as “man-made” or “not man-made” in a repetition priming task. The two groups showed different ERP responses at frontal electrode sitesafter seeing a visual stimulus for 400–800 ms. The frontal late positive components (LPC) showed differenthabituation of ERP responses to new and studied repeated objects between high and low sensation seekers.Source localization analysis (LORETA) indicated that during visual stimulus adaptation the ventral pre-frontal cortex showed lack of frontal involvement among high sensation seekers. Furthermore, frontal LPClatencies during repeated visual exposure correlated with boredom susceptibility and experience seekingsubscales. The distinct profiles of brain responses to repeated visual experience in high and low sensationseekers provide evidence that individual differences in neural adaptation can be linked to personalitydimensions.

© 2008 Elsevier Ireland Ltd. All rights reserved.

1. Introduction

Novel experiences, such as traveling to new places, tasting newfood, and experiencing new music and art, are highly rewarding tosome individuals. In contrast, repeated experiences, such as listeningto a favorite song and watching the same movie multiple times, arerewarding to others. Sensation seeking is a personality trait defined asthe tendency to seek varied, novel and complex sensations and newexperiences (e.g. Zuckerman et al., 1974, 1978; Cloninger et al., 1991;Bardo et al., 1996; Roberti, 2004). Some, but not all, of these newexperiences involve risky behavior, such as sexual experimentation,skydiving, and illegal drug use. Consequently, high sensation seekershave been found to have an increased health risk. In terms of cognitive

cience, University of Kentucky859 257 2122; fax: +1859 323

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processes, high sensation seekers tend to be proficient at dividedattention tasks, particularly those involving new experiences; but,they are less proficient in sustained attention and become easily boredwith repeated experience (Zuckerman, 1994, 2005; Brocke et al.,1999).

Recent work has begun to explore the neural correlates ofsensation seeking. Several studies have used event-related potentials(ERPs), which are voltage changes recorded on the scalp elicited bybrain activity in response to specific events. Mean amplitude of ERPlate positive components (LPC)—positive brain potentials occurringabout 300–900 ms after presentation of a stimulus—has been linkedto attention and recognition of new and previously seen stimuli (Kok,2001). Previous studies have focused on the relationship between thepersonality trait of sensation, including novelty, seeking and ampli-tude of ERP late positive components (e.g. Cloninger et al., 1991) butwith varying results. For instance, Hansenne (1999) reported thatnovelty seeking was positively correlated with LPC amplitude. Incontrast Wang and Wang (2001) reported a negative correlationbetween auditory passive LPC amplitude and sensation seeking, asdefined by Zuckerman (1994). In another study, which used an “odd-

101Y. Jiang et al. / Psychiatry Research: Neuroimaging 173 (2009) 100–106

ball” task, skydivers, who tend to be high sensation seekers, werefound to have larger frontal LPC amplitude to non-targets than thecontrol group (Pierson et al., 1999). A recent study also reported thatschizophrenia patients with high sensation seeking scores have largermemory-related LPC components (Guillem et al., 2005). A recentinvestigation by Fjell et al. (2007) suggests that ERP adaptation maybe more relevant than absolute ERP amplitude to traits of sensationseeking. The authors found that ERPs of men who participated inextreme sports (frontal P3a or “novelty-P3”) habituated more rapidlythan in other groups. Therewere no differences between the groups inoverall P3 or LPC amplitude. Additionally, previous studies have alsoreported delayed LPC among impulsive high sensation seekers (Wangand Wang, 2001; Pascalis et al., 2004). These studies demonstratesensation seeking is associated with LPC, but the specifics of therelationship vary as a function of the study context.

In the present study, we sought to provide a more detailedcharacterization of LPC responses to repeated visual experience as afunction of sensation-seeking status. Here we used a modified versionof a repetition or adaptation task to examine individual differences inbrain responses to repeated experience. Though the neural basis ofrepetition effects is still under debate (see a review by Grill-Spectoret al., 2006), a large body of literature has examined effects ofrepetition of visual objects using single-cell recording in primates (seea review by Desimone,1996), and in humans, ERP (e.g. Rugg and Nagy,1987; Bentin and McCarthy, 1994; Guo et al., 2007), fMRI (e.g. Jianget al., 2000; Henson, 2003; Yi and Chun, 2005; Mecklinger, 2006), andmultimodal imaging (Gonsalves et al., 2005) methods. The changes inthe firing properties, or numbers of neurons, activated duringrepeated presentation of stimuli allow us to differentiate visualstimuli that are previously encountered from new, or unfamiliarobjects (Wiggs andMartin, 1998). Neural responses to repeated visualitems can be altered by normal aging (e.g. Lawson et al., 2007), mentaldisorders such as Alzheimer's’ disease (Olichney et al., 2006),schizophrenia with thought disorders (Matsumoto et al., 2005), andchronic alcoholism (Zhang et al., 1997). Many cognitive andpersonality dimensions including boredom (Matthews and Desmond,1998; Thiffault and Bergeron, 2003), visual attention (Yi and Chun,

Fig. 1. Examples of the visual presentations of the repeated new and studied objects during tasked to respond to each object as “man-made” or “not man-made” by pressing a correspo

2005), emotion (Bentley et al., 2003), and judgment of self and others(Jenkins et al., 2008) can also impact the magnitude and timing ofbrain responses to repeated stimuli.

High and low sensation seekers differ in visual attention, arousal,and boredom involved with repeated experience (Zuckerman, 1994,2005). While high and low sensation seekers repeatedly classifiedvisual objects as either man-made or not man-made, we recordedtheir ERP responses. We hypothesized that differential brainresponses to repeated experience, specifically the magnitude andlatency of LPC's, would vary among high and low sensation seekers.Althoughmost previous ERP research has treated sensation seeking asa unitary construct, it is actually a multi-dimensional trait (Zucker-man, 1994; Miller et al., submitted for publication). Consequently, inorder to further investigate the neural basis underlying the differencesbetween high and low sensation seekers, we also examined therelationship between brain potentials and participant scores on FormV Sensation Seeking Scale. This scale includes four subscales(reflecting four personality components) of sensation seeking: thrilland adventure seeking, experience seeking, disinhibition, and bore-dom susceptibility (Zuckerman et al., 1978).

2. Methods

2.1. Participants

Potential volunteers were recruited from flyers, class announce-ments, and word of mouth, as well as advertisements placed in theUniversity of Kentucky campus and community newspapers inLexington, Kentucky. Volunteers were first directed to a web sitewhere they provided general health and demographic information andcompleted the 8-item Brief Sensation Seeking Scale (BSSS) (Hoyle etal., 2002). Those reporting good health and who were in the upper(scoreN32 for both males and females) or lower (score b27 for malesand b25 for females) quartiles of college-agedpopulation scores on theBSSS (based on data from Harrington et al., 2003) were contacted bytelephone and asked to complete a brief phone interview to verify theinformation provided during the web survey. From the initial group of

he learning (1a) and testing (1b) phases of the visual adaptation task. Participants werending keyboard button.

102 Y. Jiang et al. / Psychiatry Research: Neuroimaging 173 (2009) 100–106

potential volunteers, a total of 40 participants (ages 18 to 25) wereaccepted for inclusion. Subjects attended an interview/medicalscreening session and completed medical and psychological ques-tionnaires. Thesequestionnaires included locally developedhealth andpersonal history questionnaires, a 17-item drug use questionnairederived from the Addiction Severity Index (McLellan et al., 1992), thecomputerized Edinburgh Handedness Inventory (Oldfield, 1971), andthe Michigan Alcoholism Screening Test (Selzer et al., 1975).Volunteers also took an eye examination using the MIS Pocket VisionGuide. Exclusion criteria included: (1) any major medical conditions,including neurological (e.g. stroke or seizures) and psychiatric (e.g.depression, schizophrenia, panic disorder) disorders, (2) prior closedhead injury or concussion, (3) current use of medications that affectthe central nervous system, (4) current or past diagnosis of a learningdisability, and (5) left-handedness.

Each subject also completed the Sensation Seeking Scale Form V(SSS Form V) (Zuckerman et al., 1978). Each of the four subscales—experience seeking (ES), thrill seeking (TAS), disinhibition (DIS), andboredom susceptibility (BS)—contained 10 items in which partici-pants were asked to choose which of two options were mostdescriptive of themselves. The factor structure, internal consistency,convergent validity, and reliability of the SSS Form V and the subscaleshave been previously established (Roberti et al., 2003; Zuckerman,2005).

In addition to the medical questionnaire, urine samples werecollected to enable independent tests of drug use (cocaine, marijuana,amphetamines, benzodiazepines, opioids etc.) and pregnancy duringthe medical screening and prior to the data collection session. Noevidence of drug use or pregnancy was detected in any participant.Participants received financial compensation, including payments forthe medical screening ($25) and the completed session ($40), alongwith a bonus ($40) for completing the study and abstaining from druguse for the duration of the study. Data from two participants from thelow sensation seeking group and four participants from the highsensation seeking group were dropped from the study due to excessiveEEG movement artifact.

2.2. Visual stimuli and task

Pictures used as experimental stimuli consisted of line drawings ofcommon objects developed by Snodgrass and Vanderwart (1980).Stimuli were displayed on a computer screen approximately 65 cmfrom the participants, and the visual angle was approximately 7°.Object size was 8 cm by 6 cm, displayed in front of a black background.

Fig. 2. High (solid line) and low (dashed line) sensation seekers' reaction times for newperformances with newobjects, while the right panel presents performances for studied objeresults also show that high sensation seekers respond faster towards these items than low

There were two phases to the experiment, as indicated in Fig. 1.Participants initially studied a series of 100 pictures displayed for 4 seach on a computer screen. They were asked to intentionally encode(memorize) each picture object (Fig. 1a). All of the participants weretested immediately after the study phase. Subjects identified as “new”

or “old” randomly presented test pictures (half studied and half new).All subjects reached a recognition accuracy of 95–100%. Following thestudy phase, participants were fitted with the 64-channel Quick-Cap(Neuromedical Supplies) used for electroencephalogram (EEG)recording. Next, the participants completed the test phase of theexperiment: the classification of repeated pictures.

During the classification task, participants were presented withpictures of 140 commonobjects; 70were studied in thefirst phase of theexperiment and 70 were new (see Fig. 1). Immediate repetitions (1–3times) of both studied andnewobjectswere inter-mixed. For each trial, afixation cross was also presented to allow participants an opportu-nity to blink (see Fig. 1b). Participants were asked to categorize eachobject as “man-made” or “not man-made” by pressing a key on thekeyboard. Key assignment was counterbalanced across participants.Each object stimulus was presented for 1000 ms and the inter-stimulus interval (ISI) lasted between 1100 and 1900 ms(M=1500 ms). Fixations were presented for 1500 ms. The taskwas completed in about 35 min.

2.3. ERP recordings

EEGs were recorded from 64 scalp sites using Ag/AgCL electrodesembedded in an elastic cap at locations designed to cover the scalp. Twoadditional channels were used for monitoring horizontal and verticaleye movements. An electrode placed between Cz and CPz served as areference. ERP responses were later re-referenced offline to the averageof the right and left mastoid potentials. Electrode impedances did notexceed 5′Ω. EEG signalswerefilteredwith a bandpass of 0.05–40Hz andsampled at a rate of 500 Hz. Average ERPs were formed offline from alltrials and were free of ocular and movement artifacts (N±75 µV). Eachaveraging epoch lasted 900mswith anadditional 100ms recorded priorto stimulus onset to allow for baseline correction.

2.4. Statistical analyses

Behavioral effects included mean response times (RTs) for correctresponses. ERPs were averaged across correct responses elicited by eachcondition during the test phase of the task. ERP mean peak latencydatawere gathered for LPC (latency of the highest positive amplitude

and studied objects as a function of stimulus presentation. The left panel presentscts. The largest group difference is found for newobjects presented for the first time. Thesensation seekers. (Error bars represent standard error).

103Y. Jiang et al. / Psychiatry Research: Neuroimaging 173 (2009) 100–106

300–800 ms) (Picton et al., 2000). The present report focuses on theERP LPC mean amplitude data gathered at time segments 400–600,600–800, and 800–900 ms post-stimulus onset for each condition.Due to space limitations, results of the frontal negative-going FN400related to ‘old–new’ effect will be reported elsewhere. To examinegroup effects in relation to repetition and study type,mixed four-wayanalyses of variance (ANOVA) were conducted for each dependentvariable (i.e., RTs, each ERP latency and amplitudemeasure). For eachsensation seeking group (low and high sensation seekers) weevaluated object type (new, studied), repetition (first, second, andthird presentation), and electrode sites (FPz, Fz, FCz, Cz, CPz, Pz, POz,Oz; for ERP analyses). The significance level was set at 0.05, andBonferroni correction for pairwise comparisons was used whenappropriate. Greenhouse–Geisser corrections were reported with alleffects having two or more degrees of freedom in the numerator.

2.5. Source analyses

In order to localize the source of the ERP responses, supplementalanalyses were conducted for all ERP waves. We used the sLORETAmethod (standard low resolution electromagnetic tomography, viaCurry v5.0) for localizing electrical activity in the brain using aLaplacian model term that measures the second derivative of sourcestrengths (Anderer et al., 1998). Current density reconstructions(CDRs) assume simultaneous activity at a large number of possiblesource locations. Prior results have shown that LORETA producesblurred but accurate localizations of point sources in other visual

Fig. 3. ERP responses to new and studied objects in both high and low sensation seekers asrepetition. The ERP responses (LPC) reduced with repetition of a stimulus among the lowadaptation among the high sensation seeking group.

processing paradigms (e.g. Pascual-Marqui et al., 2002; Guo et al.,2007; Jiang et al., 2008). The procedure used a realistic volumeconductor model derived from a boundary element method with skin(10 mm), skull (9 mm), and brain (7 mm) layers, using conductivitiesof 0.3300, 0.0042, and 0.3300 μV, respectively.

3. Results

3.1. Behavioral results

Response time data revealed an expected main effect of repetition,F(2,64)=245.18, Pb0.001. Reaction time for all participants decreasedfrom the initial presentation of an object to its second and thirdpresentations. An interactionbetweenprior learningand repetitionwasalso significant, F (2, 64)=5.13, P=0.01. Reaction times for studiedobjects decreased steadily with each repeated presentation (Fig. 2).

3.2. ERP results

3.2.1. LPC latencyFig. 3 presents ERP responses to newand studied objects in both high

and low sensation seekers as a function of time following stimuluspresentation. For LPCpeak latency, amain effect ofGroup,F(1,32)=5.162,Pb0.05, and an interactionbetweenGroup andElectrode,F(7,224)=7.68,Pb0.001, were found. Peak LPC latencies were shorter for low(M=502.89 ms) than high (M=533.11 ms) sensation seekers, but onlyat frontal sites (i.e., FPz, Fz, FCz).

a function of electrode placement, time following stimulus presentation, and stimulussensation seekers, i.e. a clear adaptation process in LSS, but remained constant or no

Table 1Pearson correlations (n=34).

Relations between SSS subscales and LPC latency (300–800 ms)

FPz_all Fz_all FCz_all

r β r β r β

Experience seeking 0.404⁎ 0.356† 0.385⁎ 0.213 0.200 0.066Thrill & adventure seeking 0.039 −0.204 0.278 0.061 0.211 0.094Boredom susceptibility 0.318 0.226 0.610⁎⁎ 0.563⁎ 0.435⁎ 0.431⁎Disinhibition 0.230 0.090 0.255 −0.110 0.145 −0.119

† Significant at the 0.07 level; ⁎ significant at the 0.05 level; ⁎⁎ significant at the 0.01level (2-tailed).For each site (FPz, Fz, and FCz), the first column presents zero-order correlations and thesecondcolumnpresents standardized regression coefficients froma simultaneous analysis.

104 Y. Jiang et al. / Psychiatry Research: Neuroimaging 173 (2009) 100–106

3.2.2. LPC adaptationANOVAs were conducted to test the mean amplitude at 400–600,

600–800, and 800–900 ms intervals. The 4-way interactions betweengroup, study type, repetition, and electrodewere significant only for theintervals of 400–600 [F (14,448)=2.41, Pb0.05] and 600–800 ms [F(14,448)=2.45, Pb0.05]. Simple effects analyses revealed the sameeffects for both time intervals. At frontal sites, low sensation seekers hadlarger LPC responses for studied than new objects during the initialpresentation, no amplitude difference between studied and newobjectsduring the second presentation, and larger positive amplitude for newthan studied objects during the third presentation. In contrast, LPCresponses did not vary across the three presentations for high sensationseekers or across the object type (see Fig. 3). These data demonstratethat highand lowsensation seekers showdifferent LPC responses tonewand old repeated objects. That is, low sensation seekers are moresensitive to repetition of previously seen objects.

3.2.3. Correlations and regressionsDifferences between high and low sensation seekers may relate to

one or more components of the multidimensional sensation seekingpersonality trait. To explore this issue, we examined the relationshipbetween ERP LPC components and scores on the four subscales of theSSS Form V.

Since we found group differences in frontal electrode sites withrepetition, it was assumed that the adaptation process of all

Fig. 4. Frontal activity of low (LSS) and high (HSS) sensation seekers during repeated visual e(CDRs) based on the LORETA model using a color scale for CDRs as a source of designateadaptation.

presentations rather than the first presentation was a better indicatorof experience seeking or response to boredom. Thus we examined thecorrelations between SSS subscale scores and LPC latency andamplitudes of all repetitions in the Fz, FPz and FCz. The overall LPCmean amplitudes, however, did not correlate with any of thesubscales. Interestingly, we found a significant correlation of LPClatency (pooled repetitions) of frontal electrodes and the boredomsusceptibility score. Table 1 indicates that frontal LPC latency of allrepetitions (Fz, FCz, and FPz) was significantly correlated with theexperience seeking (ES) and boredom susceptibility (BS) scales. Theoverall LPC mean amplitudes, however, did not correlate with any ofthe subscales. Table 1 provides Pearson correlations between frontalLPC responses/LPC latencies and scores of each of the four subscales(Table 1), as well as providing beta weights from a simultaneousregression which controls for the overlap among subscales.

The correlations obtained from Pearson correlations, whichassumes normal distribution of the testing scores, at levels ofPb0.05 and Pb0.01 remained significant even by using the moreconservative Spearman correlation, which does not assume normaldistribution of the testing scores.

In order to further examine the predictive specificity of thesubscales, three simultaneous regressionswere conducted. LPC latencyof FPz, Fz, and FCz, collapsed across stimuli,was regressed onto the foursubscales of the SSS. Proportions of variance accounted for in the LPClatency were substantial; R2s equaled 0.23, 0.41, and 0.20 for sites FPz,Fz, and FCz respectively. For site FPz, experience seeking (ES) was theonly scale significantly related to LPC latency. The standardizedcoefficient for experience seeking was moderate in size and 1.5 timeslarger than the next largest coefficient; ES accounted for an additional10% of the variance above and beyond the other subscales (semi-partial r=0.317). For site Fz, boredom susceptibility (BS) was the onlysignificant predictor with a large effect size, more than 2.5 times largerthan the next highest effect size. BS accounted for an additional 17% ofthe variance above and beyond the other three subscales (semi-partialr=0.488). For site FCz, BS was again the sole predictor of LPC latencywith a moderate to large effect size, which was more than 3.5 timeslarger than next highest coefficient; BS accounted for an additional 14%of the variance above and beyond the other subscales (semi-partialr=0.373).

xperience (see circled area). Images are low-resolution current density reconstructionsd time points from 444–500 ms, which revealed the largest group differences in ERP

Fig. 5. Frontal LPC (mean latencies) as a function of boredom susceptibility in high andlow sensation seekers and the associated correlation coefficient (r=0.61; Pb0.01).

105Y. Jiang et al. / Psychiatry Research: Neuroimaging 173 (2009) 100–106

3.2.4. Lack of prefrontal involvement in high sensation seekersTo localize the source of LPC responses of low and high sensation

seeking, an intracranial source analysis was calculated for the timepoint with the maximal signal strength as estimated by mean globalfield power. The LORETAmethod yields images of standardized currentdensity associated with EEG responses. The source localization usedthe 444–500 ms window because the current distribution peaked atthis range. In contrast, ERP amplitude analysis used voltage of ERPresponses as measure. Nevertheless, the localization of 444–500 msfalls in the range of LPC. The source localization analysis (LORETA)indicated that during the adaptation to visual stimuli, both groupsshowed posterior activation in the visual cortices. This LPC activationoccurred predominantly in the right hemisphere, particularly in theright temporal and parietal cortices. Interestingly, low sensationseekers also revealed a frontal source in the pre-frontal cortex that isabsent in high sensation seekers (Fig. 4).

4. Discussion

To examine neural correlates of the repeated presentation of newand previously studied visual items as a function of sensation seekingstatus, we measured behavioral and ERP responses during repeatedvisual stimulus exposure among high and low sensation seekers, asdefined by self-reported responses on a validated sensation seekingpersonality scale. Frontal LPC is related to repetition of visual stimuli or‘new stimuli’ in both recognition memory tasks and in implicitfamiliarity tasks (e.g., Rugg, 1990; Paller, 2001; Curran and Friedman,2004; Gold et al., 2005; Paller et al., 2007; Rugg and Curran, 2007; Guoet al., 2007). The LPC has been found to habituate rather quickly(Friedman and Simpson, 1994), particularly among high sensationseekers (Fjell et al., 2007). Results from the present study demonstratedthat frontal LPC effects were not solely task-related; rather, these neuraleffects were observed in the context of non-task related adaptation inboth high and low sensation seeking groups.When the newand studiedvisual stimuli were presented repeatedly, ERPs of high sensation seekerswere less sensitive to repetition than those of low sensation seekers,perhaps reflecting more rapid adaptation to repeated images amonghigh sensation seekers.

To explore the basis of this difference, we further analyzedcorrelations between ERPs and scores on sensation seeking subscales.Among subscales (i.e., experience seeking, thrill and adventureseeking, boredom susceptibility, and disinhibition) the most signifi-

cant correlation was found between latency of frontal LPC andboredom susceptibility (BS, Fig. 5). High BS scores reflect a person'stendency to be bored quickly. Based on these self-reports, repeatedexperience is not their natural tendency. On the other hand, lowsensation seeking individuals tend to enjoy repetitions of a familiarexperience. They feel that “there are some movies I enjoy seeing asecond or even third time,” and “I enjoy spending time in the familiarsurroundings of home.” Self-report scores on the boredom suscept-ibility subscale were a good predictor of frontal ERP response latency.Individuals who scored high on boredom susceptibility (easily bored)showed delayed frontal LPC responses during repeated visualexposure. It is noteworthy that scores on the thrill and adventureseeking (TAS) subscale did not correlate with visual adaptation. Milleret al. (submitted for publication) recently found that TAS was the bestindicator of a more narrowly defined sensation seeking construct.However, ES, DIS, and BS are more complex, representing blends ofmultiple impulsivity-related traits—lack of premeditation, narrowsensation seeking, and urgency (a negative affect-related domain). Itshould be noted that recent results have also suggested a relationshipbetween components of sensation seeking and brain structure (Martinet al., 2007). Pascalis et al. (2004) reported that high impulsivitysubjects, compared to those with low impulsivity, showed longer LPClatencies, which is consistent with the current results that individualswho are seeking new experience and easily bored have delayed LPClatency at frontal sites. Similarly, Joseph et al. 2009 also reportedlonger delays in fMRI responses to emotional visual images amonghigh sensation seekers compared to the low sensation seekers in themid-frontal region.

The LORETA source localization revealed that only the lowsensation seekers engaged the frontal cortex during visual adaptation.Because the LORETA inverse source solutions are located on the surfaceof a glass brain, the depth of the true sources is not uniquely defined.We suspect that the brain regions involved are the orbital frontal andanterior cingulate. In the recent investigation of fMRI responses toemotional images, Joseph et al. 2009 reported that low sensationseekers showed greater activation to high arousal stimuli in brainregions involved in emotional regulation, i.e. medial orbitofrontal andanterior cingulate cortices. These regions have also been associatedwith reward, evaluation of good and bad, and emotional decisionmaking (Bechara, 2005). Furthermore, primate studies have providedevidence that neuronal activity in the orbitofrontal cortex (OFC) reflectthe importance of reward information in different contexts and timeperiods (Simmons and Richmond, 2007). Alternatively, it is alsopossible that the frontal responses reflect the inhibitory process orfrontal regulation during the classification task. Increased ERPs amonglow sensation seekers might be linked to the stronger effort tosuppress the distraction by newobjects. High sensation seekers, on theother hand, did not demonstrate frontal region activation duringadaptation.

To summarize, the frontal LPC showed distinct ERP responseprofiles with the repetition of a stimulus among the low and highsensation seeker groups. Furthermore, frontal LPC latency and meanERP responses during repeated visual exposurewere highly correlatedwith personality scores, most significantly with boredom suscept-ibility. Interestingly, source localization analysis (LORETA) indicatedthat during the adaptation of visual stimuli the left frontal cortexshowed the strongest activation in low sensation seekers. We provideevidence that the individual differences in boredom susceptibility andexperience seeking is strongly linked to the brain responses duringadaptation to repeated visual exposure.

At themethodological level, the current results support the idea thatadaptation of ERP responses, in comparison to absolute ERP amplitude,can be a better indicator of response to repeated experience. Frontal LPClatencywas found to be strongly associatedwithboredomsusceptibility.Correlation results indicated that close to 40% of the variance in scoreson the boredom susceptibility subscale could be accounted for by ERP

106 Y. Jiang et al. / Psychiatry Research: Neuroimaging 173 (2009) 100–106

responses from frontal electrodes. This result provides support for aneurobiological basis of boredom susceptibility. Finally, our LORETAresult of enhanced activation in left prefrontal cortex among lowsensation seekers associated with repeated presentation of studieditems may reflect functional differences associated with adaptation ofpreviously seen stimuli in these individuals. The present results provideadditional evidence that individual differences in response to repeatedvisual stimuli may have a biological basis that is associated with thepersonality dimensions of sensation seeking.

Acknowledgements

Parts of the results were presented at the 15th annual meeting ofSociety of Prevention Research. This research was sponsored by theNational Institutes of Health P50 DA05312 and AG00986. We thank T.Vagnini and K. Bylica for their assistance in data collection; M. Bardo,R.L. Donohew, H. Nolan, and A. Schoenfeld for their helpful comments.

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