affective style

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Affective Style and Affective Disorders:

Perspectives from Affective Neuroscience

RichardJ. Davidson

U niversity of W isconsin M adison, U SA

Individual differences in emotional reactivity or affective style can be

fruitfully decomposed into more elementary constituents. Several separable

features of affective style are identied such as the threshold for reactivity,the peak amplitude of response, the rise time to peakand the rec overy time.

The latter two characteristics constitute components of affective chronome-

try. The circuitry that underlies two fundamental forms of motivation andemotionapproach and wi thdraw al-rel ate d processe s is desc ribed. Data on

individual differences in functional activity in certain components of thesecircuits are next reviewed, with an emphasis on the nomological network of

associations surrounding individual differences in asymme tric prefrontal

activation. The relevance of such difference s for understanding the nature

of the affective dysfunction in affective disorders is then considered. Thearticle ends by considering what the prefrontal cortex ``does in certain

components of affective style and highlights some of the important ques-tions for future research.

I. INTRODUCTION

Among the most striking feature s of human emotion is the variability that

is apparent across individuals in the quality and inte nsity of disposition al

mood and emotional reactions to similar incentive s and challe nge s. The

broad ranges of differences in these varied affective phenomena has been

COGNITION AND EMOTION, 1998, 12 (3), 307330

Requests for reprints should be sent to Richard J. Davidson, Laboratory for Affective

Neuroscience, Department of Psychology, University of WisconsinMadison, 1202 West

Johnson Street, Madison, WI 53706, USA; e-mail: [email protected].

This research was supported by NIMH grants MH43454, MH40747, Research Scientist

Award K05-MH00875, and P50-MH52354 to the Wisconsin Center for Affective Scie nce(R.J. Davidson, Director), by a NARSAD Established Inve stigator Award, and by a grant

from the John D. and Catherine T. MacArthur Foundation. I thank the many individuals in

my laboratories who have contributed importantly to this research over the years, including

Andy Tomarken, Steve Sutton, Wil Irwin, Heather Abercrombie, Jeff Henriques, Chris

Larson, Stacey Schaefer, Terry Ward, Darren Dottl, Isa Dolski, as well as the many

collaborators outside my lab too numerous to name.

1998 Psychology Press Ltd


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referred to as ``affective style (Davidson, 1992 ). Differences among

people in affective style appe ar to be associated with temperament

(Kagan, Rez nick & Snidm an, 1988), personality (Gross, Sutton, & Kete-

laar, in press) and vulne rability to psyc hopathology (Meehl, 19 75). More-

over, s uch diffe rence s are not a unique hum an attribute , but appe ar to be

pres ent in a number of different specie s (e.g. Davidson, Kalin, & Shelton,

1993; Kalin, 1993).

In the next section of this article , conc eptual distinc tions among the

various components of affective style will be introduced and methodologi-

cal challenges to their study will be highlighte d. The third section will

pres ent a brief ove rview of the anatom y of tw o basic motivational/ emo-

tional system sthe approac h and withdraw al systems. Se ction four w ill

consider individual differences in these basic systems and indic ate howsuch diffe rence s m ight be studied. The fth sec tion wi ll addre ss the relation

between such individual differences and psychopathology. It is our intuition

that some of the individual differences in basic processes of affective style

are central to determining either resilience or vulnerability. Such differences

can be conceptualised as diatheses which affect an individual s response to a

stressful life event. Finally, the last section will conside r some of the

implic ations of this perspective for assessm ent, treatment and plasticity.

II. THE CONSTITUENTS OF AFFECTIVE STYLE

Many phenom ena are subsumed under the rubric of affective style. A

conc ept featured in many disc ussions of affec tive de velopment, affec tive

disorde rs and personality is `` emotion regulation (Thompson, 1994).

Emotion regulation refers to a broad constellation of processes that serve

to eithe r amplify , attenuate , or maintain the strength of emotional reac-

tions. Include d among these proc esses are certain features of attentionwhich regulate the extent to which an organism can be distracted from a

potentially aversive stimulus (Derryberry & Reed, 1996) and the capacity

for self-generated imagery to replace emotions that are unw anted, with

more desirable imagery scripts. Emotion regulation can be both automatic

and controlled. Automatic emotion regulation may result from the progres-

sive automisation of processes that initially were voluntary and controlled

and have evolved to bec ome more autom atic w ith practice. We hold the

view that regulatory processes are an intrinsic part of emotional behaviourand rarely does an emotion get generated in the absence of recruiting

associated regulatory proc esses . For this reason, it is often conc eptually

difcult to distinguish sharply between where an emotion ends and regula-

tion begins. Even more proble matic is the methodologic al challenge of

operationalis ing these different compone nts in the stream of affective

behaviour.

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Whe n considering the ques tion of individual differences in affective

behaviour, one must specify the particular response systems in which the

individual differences are being explored. It is not necessarily the case that

the same pattern of individual differences would be found across response

sys tem s. Thus, for example , an individual may have a low thres hold f or the

elicitation of the subjective experience (as ree cted in self-reports) of a

particular emotion but a relativ ely high threshold for the elicitation of a

partic ular phy siologic al change . It is important not to assum e that indiv idual

differences in any parameter of affective responding will necessarily gen-

eralise across response systems, within the same emotion. Equally impor-

tant is the question of whether individual differences associated with the

generation of a partic ular specic emotion will neces sarily generalise to

other e motions. For example , are those individuals who are behaviourallyexpressive in response to a fear challenge also likely to show comparably

high levels of expressiv ity in response to positive ince ntives? Although

systematic research on this question is still required, initial evidence sug-

gests that at least certain aspects of affective style may be emotion-specic,

or at least valence-specic (e.g. Wheeler, Davidson, & Tomarken, 1993).

In addition to emotion regulation, there are probably intrinsic differ-

ences in certain components of emotional responding. There are likely

individual differences in the threshold for eliciting compone nts of aparticular emotion, given a stimulus of a certain intensity. Thus, some

individuals are likely to produc e facial s igns of disgust on pres entation of

a partic ular inte nsity of noxious stimulus, whe reas other individuals may

require a more intense stimulus for the elicitation of the same response at

a comparable intensity . This sugg estion implie s that dose -response func -

tions may reliably differ across individuals . Unfortunate ly, systematic

studies of this kind have not been performed, in part because of the

difculty of creating stimuli that are grade d in intensity and designedto elicit the same emotion. In the olfactory and gustatory modalitie s,

there are possibilities of creating stimuli that differ systematically in

the c onc entration of a disgust-produc ing component and then obtaining

psychophys ical threshold functions that would reveal such indiv idual

diffe rences . How eve r, the produc tion of such inte nsity-g raded stimuli in

other modalities will likely be more complicated, although with the devel-

opme nt of large, normatively rated complex stimulus sets, this may be

possible. An example is the International Affective Picture System (Lang,Bradley, & Cuthbert, 1995) developed by Peter Lang and his colleagues.

This set includes a large number of visual stimuli that have been rated on

valence and arousal dimensions and that comprise locations throughout this

two-dime nsional space . The density of stimulus exemplars at all lev els

within this space allow for the possibility of selecting stimuli that are

graded in intensity for the sort of dose-response studies described above.

AFFECTIVE STYLE AND AFFECTIVE DISORDERS 309


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There are also likely to be individual differences in the peakor ampli-

tude of the response. On presentation of a series of graded stimuli that

differ in intensity, the maximum amplitude in a certain system (e.g.

intensity of a facial contrac tion, change in heart rate, etc.) is likely to

diffe r systematically across subje cts. Some individuals will respond wi th

a larger amplitude peak compared with others. Again, such individual

differences may we ll be quite speci c to particular systems and will not

necessarily generalise across systems, even within the same emotion. Thus,

the indiv idual who is in the tail of the distribution in his/he r heart rate

response to a fearful stimulus will not nece ssarily be in the tail of the

distribution in his/her facial response.

Anothe r parame ter that is like ly to differ systematically across indivi-

duals is the rise time to peak. Some individuals will rise quickly in a certainresponse system, whereas others will rise more slowly. There may be an

association between the peak of the response and the rise time to the peak

within certain systems for particular emotions. Thus, it may be the case that

for ange r-related emotion, those individuals with higher peak vocal

responses also show a faster rise time, but to the best of my knowledge,

there are no systematic data related to such differences.

Finally, another component of i ntrinsic difference s across individuals is

the recove ry time . Following perturbation in a particular system, someindividuals rec over quickly and othe rs recover slowly. For ex ample, fol-

low ing a fear-provoking encounte r, s ome individuals show a persisting

heart rate elevation that might last for minutes, whereas other individuals

show a comparable peak and rise time, but recover much more quickly. Of

course, as with other parameters, there are likely to be differences in

recovery time across different respons e systems. Some individuals may

recover rapidly in their expressive behaviour, while recovering slowly in

certain autonomic channels. The pote ntial sig nic anc e of such dissocia-tions has not been systematically examined.

The specic parameters of indiv idual differences that are delineated

abov e desc ribe a ffective chronometry the temporal dy nami c s of affec-

tive responding. Ve ry little is known about the factors that gove rn these

individual differences and the extent to which such differences are

specic to particular emotion response systems or generalise across

emotions (e.g. is the heart rate recovery follow ing fear similar to that

follow ing disgus t? ). Moreover, the general issue of the extent to whichthese diffe rent parameters that have been identied are orthogonal or

correlate d features of emotional responding is an empirical que stion

that has yet to be answered. For reasons that I hope to make clear

later, affec tive chronome try is a partic ularly important feature of affec -

tive style and is like ly to play a key role in determining vulne rability to

psychopatholog y. It is also a feature of affective style that is methodo-

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represe ntations of behavioural-re inforceme nt continge ncie s in working

memory (Thorpe, Rolls, & Maddison, 1983). In addition, output from the

me dial pref rontal cortex to nuc le us acc umbe ns ( NA) neurone s m odulate s

the transfe r of motivationally relevant i nformation through the NA (Kali-

vas, Churchill, & Klitenick, 1993). The basal ganglia are hypothesised to

be involved in the expression of the abstract goal in action plans and in the

anticipation of reward (Schultz, Apicella, Romo, & Scarnati, 1995a;

Schultz et al., 1995b). The NA, particularly the caudomedial shell region

of the NA, is a major convergence zone for motivationally relevant

information from a myriad of limbic structures. Cells in this region of

the NA increase their ring rate during reward expectation (see Schultz et

al., 1995a). There are probably other structures inv olved in this circuit

which depe nd on a number of factors including the nature of the stimulisignalli ng appe titive information, the extent to w hich the behavioural-

reinforcement contingency is novel or overlearned, and the nature of the

antic ipated behavioural response .

It should be noted that the activation of this approac h system is

hy pothe sised to be associated with one partic ular form of positiv e affec t

and not all forms of such emotion. It is specically predicted to be

associated with pre-goal attainment positive affect, that form of positiv e

affect that is elicited as an organism moves close r tow ard an appe titivegoal. Post-goal attainment positive affect represents another form of

positive em otion that is not expected to be associate d with activation of

this circuit (see Davids on, 1994 for a more extended discussion of this

distinction). This latter type of positive affect may be phenomenologically

experienced as contentment and is expected to occur when the prefrontal

cortex goes off-line after a desired goal has been achieved. Cells in the NA

have also been shown to de crease their ring rate during post-goal con-

summatory behaviour (e.g. Henriksen & Giacchino, 1993).Law ful individual difference s c an enter into many different stages of the

approac h s ystem. Such individual differences and thei r role in m odulating

vulnerabil ity to ps yc hopathology w ill be cons ide red in detail late r. For the

moment, it is important to unde rscore two issues. One is that there are

individual differences in the tonic level of activation of the approac h

system w hich alte rs an individual s prope nsity to experience approach-

related positive affect. Second, there are likely to be individual differences

in the capac ity to shift betwe en pre- and post-goal attainme nt positiveaffect and in the ratio between these two forms of positive affect. On

reaching a desired g oal, some individuals will immediate ly replac e the

just-ac hie ved goal w ith a new desired goal, and so w ill hav e little oppor-

tunity to e xperience pos t-goal attainment positive affe ct, or conte ntme nt.

There may be an optimal balance between these two forms of positive

affect, although this issue has not received systematic study.

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There appears to be a second system concerned with the neural imple-

mentation of withdraw al. This system facilitates the withdraw al of an

individual from sources of aversive stimulation and generates certain

forms of negative affect that are withdrawal-related. Both fear and disgust

are associated with increasing the distance betwe en the organism and a

source of aversive stimulation. From invasive animal studie s and human

neuroimaging studies, it appears that the amygdala is critically involved in

this system (e.g. LeDoux, 1987). Using functional magnetic resonanc e

imaging (fMRI) we have rece ntly demonstrated for the rst time activa-

tion in the hum an amyg dala i n response to av ersive pic tures compared w ith

neutral control pictures (Irwin et al., 1996). In addition, the temporal polar

region also appears to be activated during withdrawal-related emotion (e.g.

Reiman, Fusselman, Fox, & Raichle, 1989; but see Drevets, Videen,MacLeod, Haller, & Raichle, 1992a). These effects, at least in humans,

appear to be more pronounced on the right side of the brain (see Davidson,

1992 , 1993 for rev iew s). In human ele ctrophysiologi cal studies, the right

frontal region is also activated during withdrawal-related negative affective

states (e.g. Davidson, Ekman, Saron, Senulis, & Friesen, 1990 a). At

present, it is not entirely clear whether this EEG change reects activation

at a frontal site or w hether the activity rec orde d from the frontal scalp

region is volume-conducted from other cortical loci. The resolution of thisunc ertainty must aw ait additional studies using positron emiss ion tomo-

graphy (PET) or fMRI, which hav e sufc ient spatial resolution to diff er-

entiate among different anterior cortical regions. In addition to the

temporal polar region, the amygdala and possibly the prefrontal cortex, it

is als o likel y that the bas al ganglia and hypothalamus are involv ed in the

motor and autonom ic compone nts, respectively, of w ithdraw al-relate d

negative affect (see Smith, DeVito, & Astley, 1990).

The nature of the relation betwee n these two hypothe sised affect sys-tems also remains to be delineated. The emotion literature is replete with

different proposals regarding the inte rrelations among different f orms of

positive and negative affect. Some theorists have proposed a single biva-

lent dimension that rang es from unpleasant to pleasant affect, with a

second dimension that reects arousal (e.g. Russell, 1980). Other theorists

have suggested that affect spac e is best described by two orthogonal

positive and neg ative dimensions (e.g. Watson & Tellege n, 1 985). Still

other workers have sug gested that the degree of orthogonality betwee npositive and neg ative affec t depends upon the temporal frame of analysis

(Diener & Emmons, 1984). This formulation holds that when assessed in

the moment, positive and negative affect are reciprocally related, but when

examine d over a longe r time-frame (e.g. dispositional affect), they are

orthogonal. It must be emphasised that these analyse s of the relation

betwee n positive and negativ e affect are all base d exc lusive ly on me asures



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of self-report and therefore their generalisability to other measures of affect

are unc ertain. Howe ve r, based on new data to be des cribed late r, we believ e

that a grow ing corpus of data doe s inde ed indicate that one func tion of

positive affect is to inhibit concurrent negative affect.

IV. INDIVIDUAL DIFFERENCES IN ASYMMETRIC

PREFRONTAL ACTIVATION: WHAT DO THEY

REFLECT?

This section will present a brief overview of recent work from my labora-

tory des igned to e xamine individual difference s in m easures of pref rontal

activ ation and thei r relation to diffe rent aspec ts of e motion, aff ective style,

and related biologica l c ons tructs. These ndings w ill be use d to addre ss thequestion of what underlying constituents of affective style such individual

differences in prefrontal activation actually reect.

In both infants (Davidson & Fox, 1989 ) and adults (Davids on &

Tomarke n, 19 89) we notic ed that there w ere large individual differences

in baseline electrophysiological measures of prefrontal activation and that

such individual variation was associated with differences in aspe cts of

affective reactivity. In infants , Davidson and Fox (1989) reported that

10 -month-old infants who cried in respons e to maternal se paration we remore like ly to have less left and greate r right-sided prefrontal activation

during a preceding resting base line compared wi th those infants w ho did

not cry in response to this challenge. In adults, we rst noted that the phasic

in uence of positive and neg ative emotion elicitors (e.g. lm clips) on

measures of prefrontal activation asymmetry appeared to be superimposed

on more tonic individual dif ferences in the direc tion and absolute magni-

tude of asymmetry (Davidson & Tomarken, 1989).

During our initial explorations of this phenomenon, we needed todetermine if baseline ele ctrophysiolog ical m easure s of prefrontal asy mme -

try were reliable and stable over time and thus could be used as a trait-like

measure. Tomarken, Davidson, Wheeler, and Doss (1992) recorded base-

line brain electrical activity from 90 normal subje cts on two occasions

separate ly by approximate ly three we eks. At each testing session, brain

activity was recorded during eight 1-minute trials, four eyes open and four

eyes close d, presented in counte rbalanc ed order. The data were scored

visually to remove artefac t, and then Fourier-transforme d. Our focus wason power in the apha band (813Hz), although we extracted power in all

freque ncy bands (se e Davids on, C hapm an, Chapman, & Henrique s, 1990

for a discussion of power in different frequency bands and their relation to

activation). We computed coefcient alpha as a measure of internal con-

sistency reliability from the data for each ses sion. The coefc ient alphas

were quite high, with all values exceeding .85, indicating that the electro-

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physiological measures of asymmetric activation indeed showed excellent

internal consistency reliability. The test-retest reliability was adequate with

intraclass correlations rang ing from .65 to .75, depending on the spec ic

sites and methods of analysis. The major nding of import from this study

was the demonstration that measures of activation asymmetry based on

power in the alpha band from anterior scalp electrodes showed both high

internal cons istency reliability and acc eptable test-retest reliability to be

considered a trait-like index.

The large sample size in the reliability study discussed above enabled us

to sele ct a small group of e xtrem e le ft and extreme rig ht-frontally activate d

subjects for magnetic resonance imaging (MRI) scans to determine if there

existed any gross morphome tric differences in anatom ical structure

betwee n these subgroups. None of our measure s of regional volumetricasymmetry revealed any difference between the groups (unpublishe d

observations). These ndings suggest that whatever differences exist

between subjects with extreme left versus right prefrontal activation, those

differences are likely functional and not structural.

On the basis of our prior data and theory, we reasoned that extreme left

and extreme right frontally activate d subjec ts would show systematic

differences in dispositional positive and negative affect. We administered

the trait version of the Positive and Negative Affect Scales (PANAS;Watson, Clark, & Tellegen, 1988) to examine this question and found

that the left-frontally activated subjec ts reported more positive and less

negativ e affe ct than their right-frontally activate d counterparts (Tomarke n

et al., 1992; see Fig. 1, overleaf). More recently with Sutton (Sutton &

Davidson, 1997) we showed that scores on a self-report measure designed

to ope rationalise Gray s conc epts of B ehavioral Inhibition and B ehav ioral

Activation (the BIS/BAS scales; Carver & White, 1994) were even more

strongly predic ted by e le ctrophysiolog ical m easure s of pref rontal asym me-try than were scores on the PANAS scales (see Fig. 2, situated on p. 337 of

the Colour Plate Section). Subjects with greater left-sided prefrontal acti-

vation reported more relative BAS to BIS activity compared with subjects

ex hibiting more right-side d prefrontal activation.

We also hypothe sised that our measures of prefrontal asymmetry

would predict reactivity to experimental elic itors of emotion. The model

that we have developed over the past several years (see Davidson, 1992,

1994 , 19 95 for bac kground) features individual diffe rences in prefrontalactivation asymmetry as a reection of a diathe sis which modulate s

reactivity to emotionally signi cant events. According to this model,

individuals who differ in prefrontal asymmetry should respond differ-

ently to an elicitor of positive or negative emotion, even when base line

mood is partiale d out. We (Wheeler et al., 1993) performed an experi-

ment to examine this question. We presented short lm clips designed to



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elicit positive or negative emotion. Brain elec trical activity was rec orde d

prior to the presentation of the lm clips. Just after the clips were presented,

subjec ts w ere asked to rate their e motional expe rience during the prece ding

lm cli p. In addition, subje cts completed sc ale s that we re desig ned to reec t

the ir m ood at baseline . W e found that individual difference s in pref rontal

asymmetry predicted the emotional response to the lms even after thevarianc e contribute d by base line mood was statistic ally removed. Those

individuals with m ore le ft-sided prefrontal activation at base line reporte d

more positive affect to the positive lm clips and those with more right-

side d prefrontal activation reported more negative affe ct to the neg ative lm

clips. These ndings support the idea that individual differences in electro-

physiolog ical measures of prefrontal activation asymmetry mark some

aspect of vulnerability to positive and negative emotion elicitors. The fact

that such relations were obtained following the statistical removal of base-line mood indic ates that any difference betwee n left and right frontally

activated in baseline mood cannot account for the prediction of lm-

elicited emotion effects that were observed.

In a very recent study, we (Davidson, Dolski, Laron, & Sutton, in prep.)

examined relations between individual differences in prefrontal activation

asymmetry and the emotion-modulated startle. In this study, we presented

316 DAVIDSON

FIG. 1. Dispositional positive and negative affe ct (from s cores on the PANAS-General Positive

and Negative Affect Scale) in subjects who were classied as extreme and stable left-frontally

active (N = 14) and extreme and stable right-frontally active (N = 13) on the basis of electro-

physiologic al measures of base line activation asymmetries on two occasions separated by three

weeks. From Tomarken et al. (1992).


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pictures from the International Affective Picture System (Lang et al., 1995)

while acoustic startle probes were presented and the EMG-measured blink

response from the orbicularis oculi muscle region was recorded (see

Sutton, Davids on, Donzella, Irwin, & Dottl, 1997 for basic methods).

Startle probes were presented both during the 6-second slide exposure as

well as 500 milliseconds following the offset of the pictures, on separate

trials.1

We interpreted startle magnitude during picture exposure as provid-

ing an inde x related to the peak of emotional respons e, whereas startle

magnitude following the offset of the pictures was taken to reect the

recovery from emotional challenge. Used in this way, startle probe meth-

ods can potentially provide new inform ation on the time course of emo-

tional responding. We expected that individual diffe rence s during actual

picture presentation would be less pronounced than individual differencesfollowing pic ture pre sentation as an acute emotional stimulus is like ly to

pull for a normative response across subje cts, y et individuals are likely to

differ dram atically in the time to recover. Similarly, we predicted that

individual differences in prefrontal asymm etry would acc ount for more

varianc e in predic ting magnitude of recove ry (i.e . s tartle magnitude post-

stimulus) than in predicting startle magnitude during the stimulus. Our

ndings we re consistent w ith our predictions and indic ated that subje cts

with greater right-sided prefrontal activation show a larger blink magnitudefollow ing the offset of the negative stimuli, after the variance in blink

magnitude during the neg ative stimulus was partiale d out. Measure s of

prefrontal asymme try did not reliably predict startle magnitude during

picture pres entation. The ndings from this study are cons istent w ith our

hypothesis and indicate that individual differences in prefrontal asymmetry

are associated with the time course of affective responding, particularly the

recovery following emotional challenge.

In addition to the studies just desc ribed using self-report and psycho-physiolog ical measures of emotion, we have also examined relations


1In this initial study on the recovery function assessed with startle probe measures, we had

only a single post-stimulus probe at 500ms following the offset of the picture. Readers may

be surprised that the interval be tween the offset of the picture and the prese ntation of the

probe was so short. However, it should be noted that these emotional pictures are not

particularly intense and so the lingering effects of emotion follow ing the presentation ofsuch pictures is likely not to last ve ry long in most individuals. Future studies will probe

further out following the offset of the picture. Because, at most, only a single probe can be

prese nted for each picture so that habituation effec ts are minimise d, e ach new probe position

requires a substantial increase in the overall number of pictures presented. There is a nite

limit to the number of pictures contained in the IAPS. Even more importantly, we have found

that it is critical to keep the picture viewing period to well under one hour to minimise

fatigue and boredom.


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between individual differences in electrophysiolog ical measures of pre-

frontal asymme try and othe r biolog ical indic es which in turn have been

related to differential reactivity to stressful eve nts. Two rece nt e xamples

from our laboratory include measures of immune function and cortisol. In

the case of the former, we examined differences between left- and right-

prefrontally activated subjects in natural kille r cell activity, because

declines in NK activity have been reported in response to stressful,

negative eve nts (Kiecolt-Glase r & Glaser, 1991 ). We predicted that sub-

jects w ith right pre frontal activation w ould exhibit low er NK activity

compared w ith their left-activate d c ounterparts bec ause the former type

of subje ct has been found to report more dispositional negative affec t, to

show higher relative B IS activity and to respond more inte nsely to neg ativ e

em otional stimuli. We found that rig ht-frontally activate d subjec ts indeedhad lower levels of NK activity compared to their left-frontally activated

counterparts (Kang et al., 1991).

Recently, in collaboration with Kalin, our laboratory has been studying

similar individual differences in scalp-re corded measures of prefrontal

activation asymme try in rhesus monke ys (Dav idson, Kalin, & Shelton,

1992, 1993). Recently, we (Kalin, Larson, Shelton, & Davidson, in press)

acquired measures of brain electrical activity from a large sample of

rhesus monkeys (N = 50). EEG measures we re obtaine d during periodsof manual restraint. A subsample of 15 of these monke ys we re tested on

two occasions four months apart. We found that the test-retest correlation

for measures of prefrontal asymmetry was .62, suggesting similar stability

of this metric in m onke y and man. In the group of 50 animals, we also

obtaine d measures of plasma cortisol during the early morning. We

hy pothe sised that if individual diffe rences in prefrontal asym metry we re

associated with dispositional affective style, such differences should be

correlated with cortisol, because individual differences in baseline cortisolhave been related to various aspects of trait-related stressful behaviour and

psyc hopatholog y (see e.g. Gold, Goodw in, & Chrousos, 1988). We found

that animals with right-sided prefrontal activation had highe r levels of

bas eline cortisol than the ir l ef t-frontally activate d counte rparts (se e Fig.

3). Moreover, when blood samples were collected two years following our

initial testing, animals classied as showing extreme right-sided prefrontal

activation at age 1 year had signic antly highe r baseline cortisol levels

w hen they w ere 3 ye ars of age c ompared with animals w ho we re classi ed atage 1 year as displaying extreme left-sided prefrontal activation. These

ndings indicate that indiv idual difference s in prefrontal asymmetry are

present in nonhuman primates and that such differences predict biological

measures that are related to affective style.

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V. AFFECTIVE STYLE AND PSYCHOPATHOLOGY

Virtually all forms of psyc hopatholog y i nvolve some abnormality in e mo-

tional proc esse s, although the nature of these abnormalitie s is likely to

differ among different disorders. The study of precisely what is abnormal

in the emotion-proc essing systems of individuals w ith diffe rent forms of

psyc hopathology is very much at the earlie st stage s of investigation. We

have used our nding s in normal subjec ts as a foundation to probe theunderlying neural substrates of affective and anxiety disorders with a major

goal of unde rstanding more precisely the nature of the abnorm ality in

emotional-proc essi ng in affec tiv e disorde rs.

One of the important sources of data on relations between brain function

and emotion has come from studies of the affective styles of patients with

localised brain lesions (see Robinson & Downhill, 1995 for a review).

Robinson and his colleagues have reported that damage to the left frontal

region is more likely to be associated with depression than damage to anyother cortical region. Moreover, among patients with left hemisphere

damag e, more severe depressive symptomatology is present in those

patie nts whos e damage is closer to the frontal pole (Robinson, Kubos,

Starr, Rao, & Price, 1984). Studies of regional brain function with neuroi-

maging of patie nts with psyc hiatric depressions have fairly consistently

revealed a pattern of decreased blood ow or metabolism in left prefrontal


FIG. 3. Basal morning plasma cortisol from 1-ye ar-old rhesus monkeys cl assi ed as lef t (N= 1 2) ,

middle (N = 16), or right (N= 11) frontally activated based upon electrophysiological measure-

ments. From Kalin et al. (in press).


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regions at rest (Baxter et al., 1989; Bench et al., 1992; 1993; Martinot et al.,

1990; see George, Ketter, & Post, 1994 for a review; see also Drevets et al.,

1992b for a more complex pattern associated with pure familial depression).

We have conducted several studies examining regional brain electrical

activity in depression. We hypothesised that most depression is fundamen-

tally ass ociate d with a dec it in the approac h/appe titive motivation sys tem

and should therefore be specically accompanied by decreased activation

in the left prefrontal region as measured by scalp electrophysiol ogy.

Henrique s and Davidson (1991) obtaine d support for this hypothe sis.

Moreover, in another study, these authors demonstrated that the decrease

in left prefrontal activation found among depressive s was also prese nt in

recovered depressives who were currently euthymic, compared with never

depres sed c ontrols who w ere sc re ened f or lifetime history of psychopathol-ogy in both themselves as well as their rst degree relatives (Henriques &

Davidson, 1990 ). Tog ether the ndings from patie nts with localised uni-

lateral brain dam ag e, as w ell neuroimaging and e le ctrophysiology studie s

in psyc hiatric patie nts w ithout frank les ions, conve rge on the notion that

depression is associated with a decit in at least the prefrontal component

of the approach system. We view this pattern of left prefrontal hypoactiva-

tion as a neural reection of the dec reased capac ity for pleasure, loss of

interest, and generalised decline in goal-related motivation and behaviour.Consistent with this notion are the data from another recent behavioural

study from my laboratory where w e dem onstrated using signal detection

methods that depressed subjects were specically hyporeactive to reward

ince ntives (Henriques , Glow acki, & Davidson, 1994). In this study, we

adm inistered a ve rbal me mory task under rew ard, punis hment, and neutral

incentive conditions. The rewards and punishments were monetary. Signal

detection measure s of sensitivity and response bias we re c ompute d. Non-

depressed control subjec ts exhibite d a more liberal response bias unde rboth reward and punishment incentives. In other words, they were more

likely to consider a stimulus as a signal if they were rewarded for correct

hits or punishe d for misses. Depressed subjects show ed a pattern quite

sim ilar to the controls in response to the punishme nt conting ency. How -

ever, they failed to modify their response bias during the reward condition.

In other words, the depressed subjec ts we re less respons ive to rewards

compared with controls, however, the groups showed no signicant differ-

ences in response to punishment.Based on the evidence reviewed earlier, we hypothesised that in contrast

to depressi on, anxie ty disorde rs would be associate d with an increase in

right-sided rather than a decrease in left-sided prefrontal activation, parti-

cularly during an acute episode of anxie ty. To test this hypothe sis, we

(Davidson, Marshall, Tomarken, & Henriques , 1997 ) exposed social

phobic s who we re particularly fearful of making public speec hes to the

320 DAVIDSON


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16/24

volume). However, from what is known from both the animal and human

studies, it appears that the amyg dala plays an im portant role in assigning

affective signicance, particularly of negative valence, to both sensory as

we ll as cognitive input (see LeDoux , 1992 for a review ). Using positron

emission tomography (PET) to measure regional blood ow, several groups

have reported increased blood ow in the amygdala in response to both

behavioural (e.g. Schneider et al., 1995) and pharmacological (e.g. Ketter

et al., 1996) elicitors of negative affect. We have recently reported activa-

tion in the human amygdala using functional magnetic resonance imaging

(fMRI) in response to aversive pictures (Irwin et al., 1996). These studies

suggest that activation in the human amygdala occurs in respons e to a

broad range of elicitors of negative affect.

B oth fMRI and

15

O PET are ill-suited, for different reasons, for exam-ining individual differences in resting or baseline levels of activation in the

amygdala. As it is currently used, fMRI requires that at least two conditions

be compared. What is measured is a relative difference in MR signal

intensity between two or more conditions. Currently, fMRI is not cali-

brated in real physiological units. Although 15

O PET can be calibrated in

real units, it reec ts activity ove r a very short period of time (approxi-

mately one minute) and thus, for psychometric reasons, is poorly suited to

capture trait-like diffe rence s. (It w ould be the equivale nt of deve loping asing le-item self-report instrument for assessing individual differences.)

PET used with uorodeoxyglucose (FDG) as a tracer, on the other hand,

is we ll-suite d to capture trait-like effects because the period of active

uptake of tracer in the brain is approximately 30 minutes. Thus, it is

inhe rently more reliable as the data re ect activity aggre gated ov er this

30-minute period. We have used resting FDG-PET to examine individual

diffe rences in glucose metabolic rate in the amygdala and its relation to

dispositional neg ative affect in depressed subjec ts (Abercrombie et al.,submitted). We acquired a resting FDG-PET scan as well as a structural

MR scan for each subject. The structural MR scans are used for anatomical

localisation by coregistering the two image sets. Thus, for each subject, we

used an automated algorithm to t the MR scan to the PET image. Regions

of interest (ROIs) were then drawn on each subjects MR scan to outline

the amygdala in each he misphere. These ROIs we re drawn on coronal

sections of subjec ts MR images and the ROIs were then autom atically

transferred to the coregistered PET images. Glucose metabolism in the leftand right amygdala ROIs were then extracted. The inter-rater reliability for

the e xtrac ted gluc ose metabolic rate is highly signicant with intrac lass

correlations betwee n tw o inde pendent raters .97. Figure 4 (situated on

p. 338 of the Colour Plate Section) illustrates ROIs drawn around the amyg-

dala on MR sc ans of three subje cts and the associated coregistered PET

image s f rom the same subje cts. We found that subje cts wi th greate r gluc ose

322 DAVIDSON


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metabolism in both the right and left amygdala report greater dispositional

negativ e affec t on the PANAS s cale (se e Fig. 5). These ndings indicate that

individual differences in resting glucose metabolism in the amyg dala are

pres ent and that the y predict dis positional negative affec t among depres sed

subjec ts. Most nonde pressed controls score so low on the PANAS trait

negativ e scale that it is not possible to e xamine the same relation in this

group because of the severe truncation of range for the PANAS scores.

The ndings reviewed in this section indic ate that the framework

adopte d for the study of individual diffe rence s in fundame ntal approac h

and withdraw al-re lated proce sses can be usefully applie d in the study of

psyc hopathology. A de cit i n the approac h s ystem is vie we d as a unique

attribute of depressive disorders that is reected in decreased left prefrontal

activation. The acute symptoms of anxiety, as was described in our studywith social phobic s, was associated with a pronounc ed increase in both

right-sided prefrontal and parietal activation. From research conducted in

our laboratory as we ll as rece nt nding s in the literature, it appears that


FIG. 5. Scatter plot of correlations between dispositional negative affect assessed with the

PANAS-General Negative Affect Scale and PET MRI-coregi stration-deriv ed regi onal glucose

metabolism in the left and right amygdalae for all subjects (N = 17). Subjects were tested on

two different PET cameras. Those tested in a Siemens CTI 933/04 PET camera are displayed by

closed squares and those tested in the GE A dvance are depicted by the open squares. From

Abercrombie et al. (submitted).


18/24

amygdala activation may be a generic component of negative affect that is

pres ent in both anx iety and depression. Thus, difference s betwee n these

disorders may be more pronounced for cortical systems that are critically

involve d in affect regulation and affect-cognition interaction, whereas

subc ortic al contribution (in partic ular, the amygdala) may be common to

both types of disorde rs and may in part be responsible for the substantial

comorbidity between these disorders (Watson et al., 1995).

VI. IMPLICATIONS AND CONCLUSIONS

Earlier in this article, the constituents of affective style were described. We

cons idered individual differences in threshold, peak amplitude , rise time to

peak, and recovery time. Together, these constitute parameters of affectivechronometry and dictate important features of the time course of affective

responding. Following a description of the functional neuroanatomy of the

approac h and withdraw al systems, individual differences in prefrontal

activation asymmetry we re discussed and their relation to affec tive style

and psyc hopatholog y desc ribed. In the light of this information, we now

return to the question posed in the title of Section IV: What do individual

differences in prefrontal asymmetry reect?

On the basis of ndings from several new studies in my laboratory, Isuggest that at least one important compone nt of what prefrontal cortex

``doe s in affec tive responding is modulate the time course of emotional

responding, particularly recovery time. There are se veral facts critical to

making this claim. First, there are extensive reciprocal connec tions

between amygdala and the prefrontal cortex (PFC), particularly the medial

and orbital zones of the PFC (Amaral, Price, Pitkane n, & Carmichael,

1992). The glutamate rgic efferents from the PFC likely synapse on

GABA (gamma-aminobutyric acid) neurone s (Amaral et al., 1992) andthus provide an important inhibitory input to the amygdala. Sec ond,

LeDoux and his colleague s (Morgan, Romanski, & LeDoux, 1993; but

see Gewirtz, Falls, & Davis, 1997) dem onstrate d in rats that lesions of

medial prefrontal cortex dramatically prolong the maintenance of a condi-

tione d ave rsive response. In other words, animals with medial prefrontal

le sions retain ave rsiv e assoc iations for a much longe r duration of time than

normal animals. These nding s imply that the medial PFC normally

inhibits the amygdala as an active component of extinction. In the absenceof this normal inhibitory input, the amygdala remains unchecked and

continue s to maintain the learned aversive respons e. Third, are the data

from my laboratory cited i n Se ction IV, indic ating that individual differ-

ences in prefrontal activation asy mmetry signi cantly predict the magni-

tude of the post-stimulus startle follow ing removal of the varianc e

attributable to startle magnitude during the presentation of the emotional

324 DAVIDSON


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pic ture. In partic ular, left prefrontal activation appe ars to facilitate tw o

proces ses sim ultaneously: (1) it maintains representations of behav ioural-

reinforc ement continge ncie s in w orking mem ory (Thorpe et al., 1983 ); (2)

it inhibits the amygdala. In this way, the time course of negative affect is

shortened whereas the time course of positive affect is accentuated. Finally,

fourth, new ndings using PET from my laboratory indicate that in normal

subjects, glucose metabolism in left medial and lateral prefrontal cortex is

strongly associate d reciprocally with gluc ose metabolic rate in the amyg-

dala (Abercrombie et al., 1996). Thus, subjects with greater left-sided

prefrontal metabolis m hav e low er metabolic activity in their amygdala.

These ndings are consistent with the lesion study of LeDoux and collea-

gues and imply that prefrontal cortex plays an important role in modulating

activity in the amygdala. At the same time, the left prefrontal cortex is alsolikely to play a role in the mainte nance of reinforc ement-relate d beha-

vioural approach. Perhaps the dam ping of negative affec t and shorte ning

of its time course facilitates the maintenance of approach-related positive

affect.

The que stions that are feature d in this article are more tractable now

than ever before. With the advent of echoplanar methods for rapid func-

tional magnetic resonance imaging (MRI), sufcient data can be collected

within individuals to examine functional connec tions among regionshypothes ise d to constitute important ele ments of the approac h and w ith-

drawal circuits discussed earlier. Individual differences in different aspects

of these systems can then be studied with greater precision. Functional

magnetic resonanc e imaging (fMRI) methods also lend themselves to

address questions related to affective chronometry. In particular, we can

calculate that the slope of MRI signal inte nsity decline s follow ing the

offset of an aversive stimulus to provide an index of the rapidity of

recovery from activation in select brain regions. Positron emission tomo-graphy (PET) methods using new radioligands that permit quantication of

receptor density for specic neurotransmitters in different brain regions is

yie lding ne w insights directly relevant to que stions about affective style

(see e.g. Farde, Gustav sson, & Jonsson, 19 97). Trait-like diffe rences in

affective style are likely reected in relatively stable differences in char-

acteristics of the underlying neurochemic al s ystems. Using PET to ex amine

such individual differences promises to provide important syntheses

betwe en neuroc hemical and neuroanatomic al approac hes to unde rstandingthe biological bases of affective style.

Affective neuroscience seeks to unde rstand the unde rlying prox imal

neural subs trates of ele mentary cons titue nts of emotional proce ssing. In

this article , I have provide d a mode l of the functional neuroanatom y of

approac h and withdraw al m otivational/e motional sys tems and illustrate d

the many varieties of individual differences that might occur in these



20/24

systems. Research on prefrontal asymmetries associate d with affective

style and psyc hopathology was used to illustrate the pote ntial promise of

some initial approaches to the study of these questions. Modern neuroima-

ging methods used in conjunction with theoretically sophis tic ated mode ls

of emotion and psychopathology offer great promise in advanc ing our

unde rstanding of the basic mec hanism s giving rise to affective style and

affective and anxiety disorders.

Manuscript received 17 June 1997

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