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AcknowledgementsWe are grateful to M. Glickstein and D. Press for helpful discus-sions, and to M. Casement and D. Cohen for their thoughtfulcomments on this manuscript. The National Alliance forResearch in Schizophrenia and Depression (E.M.R.), the NationalInstitutes of Health (A.P.L.) the Goldberg Foundation (A.P.L.) andthe Wellcome Trust (R.C.M.) financially supported this work.

Competing interests statementThe authors declare that they have no competing financial interests.

Online links

FURTHER INFORMATIONEncyclopedia of Life Sciences: http://www.els.net/learning and memoryAccess to this interactive links box is free online.

The discipline of affective neuroscience isconcerned with the neural bases of emotionand mood. The past 30 years havewitnessed an explosion of research inaffective neuroscience that has addressedquestions such as: which brain systemsunderlie emotions? How do differences inthese systems relate to differences in theemotional experience of individuals? Dodifferent regions underlie different emotions,or are all emotions a function of the samebasic brain circuitry? How does emotionprocessing in the brain relate to bodilychanges associated with emotion? And,how does emotion processing in the braininteract with cognition, motor behaviour,language and motivation?

How are emotions and moods embodied in the brain? This is the central question that is posed by affective neuroscience — an endeavour that integrates the efforts of psychologists, psychiatrists, neurologists,philosophers and biologists. Affective

neuroscience uses functional neuroimaging,behavioural experiments, electrophysiologicalrecordings, animal and human lesion studies,and animal and human behavioural experi-ments to seek a better understanding ofemotion and mood at the neurobiological andpsychological levels and their interface.

In this article, I outline the historical development of affective neuroscience (seeTIMELINE). I begin by reviewing the pioneer-ing work of William James1 and CharlesDarwin2. This is followed by discussion of theearly functional neuroanatomical models of emotion of Walter Cannon and PhilipBard3–6, James Papez7 and Paul MacLean8. Ithen briefly outline our current knowledge ofthe contributions of key brain regions,including the prefrontal cortex (PFC), amyg-dala, hypothalamus and anterior cingulatecortex (ACC), to the processing of emotions,before considering contemporary theoreticalaccounts of how these regions might interact.Finally, some thought is given to the futuredirections of affective neuroscience.

Two fathers of affective neuroscienceIn 1872, Charles Darwin published a ground-breaking book — The Expression of theEmotions in Man and Animals2. It was the culmination of 34 years of work on emotionand made two important contributions to the field. The first was the notion that animalemotions are homologues for human emo-tions — a logical extension of Darwin’s earlywork on evolution9. Darwin sought to showthis by comparing and analysing countlesssketches and photographs of animals andpeople in different emotional states to revealcross-species similarities (FIG. 1). He also pro-posed that many emotional expressions inhumans, such as tears when upset or baringthe teeth when angry, are vestigial patterns ofaction. The second contribution was theproposal that a limited set of fundamental or‘basic’ emotions are present across speciesand across cultures (including anger, fear,surprise and sadness).

These two ideas had a profound influenceon affective neuroscience by promoting theuse of research in animals to understandemotions in humans and by giving impetusto a group of scientists who espoused the viewthat different basic emotions had separableneural substrates10.

Around 10 years later, James, in his seminalpaper entitled ‘What is an Emotion?’1, contro-versially proposed that emotions are no morethan the experience of sets of bodily changesthat occur in response to emotive stimuli. So,if we meet a bear in the woods, it is not thecase that we feel frightened and run; rather,running away follows directly from our perception of the bear, and our experience ofthe bodily changes involved in running is theemotion of fear. Different patterns of bodilychanges thereby code different emotions.Similar ideas were developed in parallel byCarl Lange in 1885 (REF. 11), providing us withthe James–Lange theory of emotions.

The James–Lange theory was challengedin the 1920s by Cannon3,4 on several grounds:total surgical separation of the viscera fromthe brain in animals did not impair emotionalbehaviour; bodily or autonomic activity cannot differentiate different emotional states; bodily changes are typically too slow togenerate emotions; and artificial hormonalactivation of bodily activity is insufficient to generate emotion. Recent research has cast doubt on Cannon’s claims. Emotionalresponses can be distinguished (at leastpartly) on the basis of autonomic activity12;emotions were less intense when the brain was disconnected from the viscera in Cannon’s studies; and some artificial manipulations of organ activity can induce

The emotional brainTim Dalgleish

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model elaborated on Papez’s and Cannon andBard’s original ideas and integrated them withthe knowledge provided by the seminal workof Kluver and Bucy. In 1939, Kluver andBucy14 had shown that bilateral removal of the temporal lobes in monkeys led to a characteristic set of behaviours (the‘Kluver–Bucy syndrome’) that included a lossof emotional reactivity, increased exploratorybehaviour, a tendency to examine objectswith the mouth, hypersexuality and abnormaldietary changes, including copraphagia (eat-ing of faeces). These studies indicated a keyrole for temporal lobe structures in emotion— a centrepiece in MacLean’s theory.

MacLean viewed the brain as a triune archi-tecture15. The first part is the evolutionarilyancient reptilian brain (the striatal complexand basal ganglia), which he saw as the seat ofprimitive emotions such as fear and aggression.The second part is the ‘old’ mammalian brain(which he originally called the ‘visceral brain’),which augments primitive reptilian emotionalresponses such as fear and also elaborates thesocial emotions. This brain system includesmany of the components of the Papez circuit— the thalamus, hypothalamus, hippocampusand cingulate cortex — along with importantadditional structures, in particular the amyg-dala and the PFC. Finally, the ‘new’ mam-malian brain consists mostly of the neocortex,which interfaces emotion with cognition andexerts top–down control over the emotionalresponses that are driven by other systems.

MacLean’s essential idea was that emotionalexperiences involve the integration of sensa-tions from the world with information fromthe body. In a neo-Jamesian view, he proposedthat events in the world lead to bodily changes.Messages about these changes return to thebrain where they are integrated with ongoingperception of the outside world. It is this inte-gration that generates emotional experience.MacLean proposed that such integration wasthe function of the visceral brain, in particularthe hippocampus, and three years later heintroduced the term ‘limbic system’ for the visceral brain16.

MacLean’s limbic system concept survivesto the current day as the dominant conceptu-alization of the ‘emotional brain’, and thestructures that he identified as important havebeen the focus of much of the research inaffective neuroscience since his original publi-cation. However, the notion of the limbic sys-tem has more recently been criticized on bothempirical17 and theoretical grounds18. A num-ber of the limbic system structures — the hip-pocampus, the mammiliary bodies and theanterior thalamus — seem to have a muchsmaller role than MacLean imagined. Some of

brain lesions to understand emotions, basedon the logic that any changes after surgerymust reflect processes that involved thelesioned part of the brain.

The Papez circuit. In 1937, James Papez pro-posed a scheme for the central neural circuitry of emotion — now known as the‘Papez circuit’7 (FIG. 2). Papez proposed thatsensory input into the thalamus diverged intoupstream and downstream — the separatestreams of ‘thought’ and ‘feeling’. The thoughtstream was transmitted from the thalamus tothe sensory cortices, especially the cingulateregion. Through this route, sensations were turned into perceptions, thoughts andmemories. Papez proposed that this streamcontinued beyond the cingulate cortexthrough the cingulum pathway to the hippo-campus and, through the fornix, to the mammillary bodies of the hypothalamus andback to the anterior thalamus via the mammil-lothalamic tract. The feeling stream, on theother hand, was transmitted from the thala-mus directly to the mammillary bodies,allowing the generation of emotions (withdownward projections to the bodily systems),and so via the anterior thalamus, upwards to the cingulate cortex. According to Papez,emotional experiences were a function ofactivity in the cingulate cortex and could begenerated through either stream. Downwardprojections from the cingulate cortex to the hypothalamus also allowed top–down cortical regulation of emotional responses.Papez’s paper was a remarkable achievement,especially given that it was allegedly written injust a few days. Many of the pathways thatPapez proposed exist, although there is less evidence that all the regions he specified arecentral to emotion.

MacLean’s limbic system. A more broadlysupported anatomical model (in terms ofcurrent data) of the brain regions that areinvolved in emotion was proposed by PaulMacLean in 1949 (REF. 8) (FIG. 3). MacLean’s

emotions — for instance, intravenous administration of cholecystokinin (a gastric peptide) can provoke panic attacks13.

The James–Lange theory has remainedinfluential. Its main contribution is theemphasis it places on the embodiment ofemotions, especially the argument thatchanges in the bodily concomitants ofemotions can alter their experienced intensity. Most contemporary affective neuroscientists would endorse a modifiedJames–Lange view in which bodily feedbackmodulates the experience of emotion (see below).

Early neuroanatomical theories The Cannon–Bard theory. Cannon’s criticismof the James–Lange theory arose from hisinvestigations with Bard of the effects of brainlesions on the emotional behaviour of cats.Decorticated cats were liable to make sudden,inappropriate and ill-directed anger attacks— a phenomenon that Cannon and Bardlabelled ‘sham rage’. Cannon and Bard arguedthat if emotions were the perception of bodilychange, then they should be entirely depen-dent on having intact sensory and motor cortices. They proposed that the fact thatremoval of the cortex did not eliminate emotions must mean that James and Langewere wrong.

On the basis of data such as these, Cannonand Bard proposed the first substantive theory of the brain mechanisms ofemotion5,6. They argued that the hypothala-mus is the brain region that is involved in theemotional response to stimuli and that suchresponses are inhibited by evolutionarilymore recent neocortical regions. Removal ofthe cortex frees the hypothalamic circuit fromtop–down control, allowing uncontrolledemotion displays such as sham rage.

Cannon and Bard’s work illustrates thebenefits of two important methodologies inaffective neuroscience. First, the use of animalemotions as human homologues, as proposedby Darwin2. And second, the use of surgical

Figure 1 | Darwin’s drawings. Drawings and photographs used by Darwin2 to illustrate cross-speciessimilarities in emotion expression — in this case, anger/aggression.



The amygdalaThe original work on Kluver–Bucy syndrome14

involved surgical removal of almost the entiretemporal lobes in monkeys. However,Weiskrantz19 showed that bilateral lesions ofthe amygdala were sufficient to induce theorality, passivity, strange dietary behaviour andincreased exploratory tendencies of the syndrome. Removal of the amygdala also permanently disrupted the social behaviour ofmonkeys, usually resulting in a fall in socialstanding20. The aspiration lesions used in theseearly studies were anatomically inexact.However, more recent studies involvingibotenic acid lesions have provided similarresults, albeit with less severe Kluver–Bucybehaviours21,22. This line of research establishedthe amygdala as one of the most importantbrain regions for emotion, with a key role in processing social signals of emotion (partic-ularly involving fear), in emotional condition-ing and in the consolidation of emotionalmemories.

The amygdala and social signals of emotion.Selective amygdala damage in humans is rarebut seems not to lead to many Kluver–Bucysigns23.A Kluver–Bucy-like syndrome becomesapparent in humans only after more extensivebilateral damage, including the rostral tempo-ral neocortex24. One of the first studies ofhuman amygdala lesions showed that amyg-dala damage can lead to impairments in theprocessing of faces and other social signals25.This finding builds on single-unit recordingstudies in animals that have shown that amyg-dala neurons can respond differently to differ-ent faces26 and can respond selectively todynamic social stimuli such as approach

them seem to be more involved in higher cog-nitive processes such as declarative memory.Nevertheless, other brain regions identified byCannon and Bard, Papez and MacLean seemto be integral to emotional life — notably, the‘reptilian brain’ (the ventral striatum and thebasal ganglia) and the limbic structures of theamygdala, hypothalamus, cingulate cortex andPFC. In the next four sections, I examine howresearch on these four limbic regions has

developed since MacLean’s original paper (FIG. 4). Other brain regions (the thalamus,nucleus accumbens, ventral pallidum, hippo-campus, septum, insula, somatosensory cortices and brain stem) have also been impli-cated in the processing of emotion; however,detailed discussion of these areas is beyond the scope of this review (but see below for adiscussion of the insular cortex and its potential involvement in disgust).

Sensory cortex Cingulate cortex

Hypothalamus

Hippocampus Anterior thalamus

Thalamus

Feeling

Emotional stimulus Bodily response

1

23

4

Figure 2 | The Papez circuit theory of the functional neuroanatomy of emotion. Papez7 argued thatsensory messages concerning emotional stimuli that arrive at the thalamus are then directed to both thecortex (stream of thinking) and the hypothalamus (stream of feeling). Papez proposed a series ofconnections from the hypothalamus to the anterior thalamus (1) and on to the cingulate cortex (2).Emotional experiences or feelings occur when the cingulate cortex integrates these signals from thehypothalamus with information from the sensory cortex. Output from the cingulate cortex to thehippocampus (3) and then to the hypothalamus (4) allows top–down cortical control of emotionalresponses. Modified, with permission, from REF. 17 (1996) Joseph Ledoux. Used by permission ofSimon and Schuster.

Harlow describesthe effects ofprefrontal cortexdamage toPhineas Gage54

William Jamesproposes hisbodily theoryof emotion1

Charles Darwin publishesThe Expression of Emotionsin Man and Animals2

Lange proposesa similar theory toJames11

Mills first proposesa right hemispherehypothesis ofemotion89

Kluver and Bucypublish their work ontemporal lobectomy14

The Cannon–Bardtheory of emotion isoutlined3–6

MacLean proposeshis tripartite ‘limbic’model of emotion8

Schachter and Singerdescribe experimentsindicating the importanceof cognitive factors indetermining the nature ofemotion experience59

Weiskrantz describesthe effects of amygdalaablation in monkeys19

Hess and Bruggerdescribe their work onsingle cell recording inthe hypothalamus82

Timeline | Historical milestones in understanding the emotional brain

Papez outlines histheory of emotion7

Schneirla outlines anapproach–withdrawalmodel of emotion95

Pribram and Nautapropose earlyversions of thesomatic markerhypothesis65,66

Gray publishes TheNeuropsychology of Anxiety97

Lazarus argues thecase for emotionsrequiring cognition121

Ekman andcolleaguespropose thatdifferent basicemotions can bedistinguishedautonomically12

1868 1872 1884 1885 1912 1931 1937 1943 1949 1956 1962 1970 1975 1980 1982 1983

Mandler publishesMind and Emotion60

Zajonc arguesthe case foremotion in theabsence ofcognition44



did not respond differentially to emotionalfaces when attentional resources were recruitedelsewhere, indicating that emotional process-ing in the amygdala is susceptible to top–downcontrol37.

The amygdala and fear conditioning. In fearconditioning, meaningless stimuli come toacquire fear-inducing properties when theyoccur in conjunction with a naturally threat-ening event such as an electric shock. Forexample, if a rat hears a tone followed by ashock, after a few such pairings it will respondfearfully to the tone, showing alterations inautonomic (heart rate and blood pressure),endocrine and motor (for example, freezing)behaviour, along with analgesia and somaticreflexes such as a potentiated startle response.Fear conditioning has been extensively stud-ied (mostly in animals), prototypically by Blanchard and Blanchard38, and morerecently and extensively by LeDoux and colleagues39–43, among many others. This bodyof research has highlighted the roles of twoafferent routes involving the amygdala thatcan mediate such conditioning. The first is adirect thalamo–amygdala route that canprocess crude sensory aspects of incomingstimuli and directly relay this information tothe amygdala, allowing an early conditionedfear response if any of these crude sensory elements are signals of threat. This echoespsychological ideas about emotion activation,notably Zajonc’s position regarding emotionswithout cognition44. The second route is athalamo–cortico–amygdala pathway thatallows more complex analysis of the incomingstimulus and delivers a slower, conditionedemotional response.

Fear conditioning in humans has been lessextensively studied. However, there have beena number of important findings. One study,by Angrilli and colleagues45, described a manwith extensive right amygdala damage whoshowed a reduced startle response to a suddenburst of white noise. The patient also seemedrelatively immune to fear conditioning, as thisstartle response was not potentiated by thepresence of aversive slides to provide an emo-tional backdrop — a technique that reliablypotentiates startle in healthy subjects. Anotherstudy, by Bechara and colleagues46, describeda patient with bilateral amygdala damage whoagain failed to fear-condition to aversive stim-uli, but who could nevertheless report thefacts about the conditioning experience. Bycontrast, another patient with hippocampaldamage successfully acquired a conditionedfear response but had no explicit memory ofthe conditioning procedure — indicating thatfear conditioning depends on the amygdala.

the amygdala in response to the presentation offearful faces. The amygdala is also selective forcertain emotions, especially fear, in vocalexpressions33. Such activation of the amygdalaby fearful faces occurs even when the faces arepresented so quickly that the subject is unawareof them34,35, or are presented in the blind hemi-field of patients with blindsight36. Nevertheless,there is evidence that amygdala activation canbe modulated by attention. Pessoa and col-leagues, for example, showed that the amygdala

behaviour27. Later studies28,29 indicated that theprocessing of emotional facial expressions,especially fear, was particularly impaired inhumans with amygdala lesions30. This involve-ment of the amygdala in the processing of facial expression has been supported byfunctional neuroimaging studies. Morris andcolleagues, using positron emission tomo-graphy (PET)31, and Breiter and colleagues,using functional magnetic resonance imaging(fMRI)32, showed selective brain activation in

Figure 3 | MacLean’s limbic system theory of the functional neuroanatomy of emotion. The corefeature of MacLean’s limbic system theory8 was the hippocampus, illustrated here as a seahorse.According to MacLean, the hippocampus received sensory inputs from the outside world as well asinformation from the internal bodily environment (viscera and body wall). Emotional experience was afunction of integrating these internal and external information streams. HYP, hypothalamus. Reproduced,with permission, from REF. 8 (1949) Lippincott Williams and Wilkins.

LeDoux proposesmultiple amygdalapathways for fearconditioning43

Damasio outlineshis somatic markerhypothesis61

Panksepp coins the term‘affective neuroscience’122

Adolphs et al. describeimpaired recognition ofemotion in facialexpressions followingbilateral damage to thehuman amygdala28

Bechara et al. showthat the amygdala isnecessary for fearconditioning but notfor explicit memory ofthe conditioningexperience46

Cahill et al. revealhow the amygdalais important in theconsolidation ofemotionalmemories51

Phillips et al. proposethat the insula is aspecific neuralsubstrate for perceivingfacial expressions ofdisgust106

Damasio et al. publish evidence that different brainregions underlie different emotions103

Lawrence et al.show how sulpirideselectively impairs facial recognition ofanger112

Calder et al.describe a patient with damage to theinsula and basal ganglia who showed impairedrecognition and experience of disgust108

Lambie and Marcel publish their theory ofconscious emotion experience117

Hariri et al. show that amygdala response to emotive stimulivaries as a function of serotonin transporter gene variation118

1986 1991 1992 1994 1995 1996 1997 2000 2002



and brain imaging studies of humans and animals and derive from the pioneering workof Mowrer in the 1950s and 1960s (REF. 58). (ForRolls’s conceptualization of emotions in termsof reward, see later in text.)

The PFC and bodily signals. As discussedabove, the James–Lange theory of the embodi-ment of emotions was heavily criticized byCannon. However, since the mid-twentiethcentury there has been a revival of a modifiedversion of the James–Lange approach, whichproposes that bodily signals interact with otherforms of information to modulate emotionalintensity, rather than being the single deter-mining factor. In 1962, Schachter and Singer59

showed that similar patterns of bodily arousalcould be experienced as anger or happinessdepending on the social and cognitive context.Such studies on the interaction of bodily infor-mation and cognition to generate emotionalexperience provided the substrate for one ofthe more influential cognitive theories of emo-tion, as outlined by Mandler in 1975 (REF. 60).More recently, Damasio and colleagues havecontinued this tradition of promoting a keyrole for bodily feedback in emotion, this timeimplicating the PFC (especially the ventro-medial PFC), with their presentation of thesomatic marker hypothesis61–64. The somaticmarker hypothesis builds on the earlier workof Nauta65, who used the term ‘interoceptive’markers rather than somatic markers, andPribram66, who used the phrase ‘feelings asmonitors’, and reflects the original ideas ofJames and Lange. Basically, somatic markersare physiological reactions, such as shifts inautonomic nervous system activity, that tagprevious emotionally significant events.Somatic markers therefore provide a signaldelineating those current events that have hademotion-related consequences in the past.Damasio argues that these somatic codes areprocessed in the ventromedial PFC, therebyenabling individuals to navigate themselvesthrough situations of uncertainty where decisions need to be made on the basis of theemotional properties of the present stimulusarray. In particular, somatic markers allowdecisions to be made in situations where a logical analysis of the available choices provesinsufficient.

Damasio’s group has used human lesionstudies to support these arguments. In 1991(REF. 67), they described the patient ‘EVR’ — a“modern day Phineas Gage”62 — whose cog-nitive functioning and explicit emotionalknowledge were more or less intact but whohad great difficulty with situations of uncer-tainty where the subtle emotional values ofmultiple stimuli need to be processed (for

Morris and colleagues showed that the amyg-dala was activated differentially in response tofear-conditioned angry faces that had beenpreviously paired with an aversive noise, com-pared with angry faces that had not beenpaired with noise35. In line with LeDoux’sideas47, there is also evidence from functionalneuroimaging that such conditioning to facesoperates by a subcortical thalamo–amygdalaroute. Finally, as well as its role in fear condi-tioning, the amygdala has also been implicatedin appetitive conditioning48.

The amygdala and memory consolidation. In aseminal study, Cahill and colleagues reportedon a patient with amygdala damage who didnot show the usual enhanced memory foremotional aspects of stories (compared withnon-emotional aspects)49. This was confirmedin another patient with nearly selective amygdala damage50. Subsequent PET studiesshowed that levels of glucose metabolism inthe right amygdala during encoding could pre-dict the recall of complex negative or positiveemotional stimuli up to several weeks later51,52.These studies indicate that the amygdala isinvolved in the consolidation of long-termemotional memories. As well as its role inmemory, the amygdala has been associatedwith the modulation of other cognitiveprocesses, such as visual perception53.

The PFCIn 1848, Phineas Gage, a construction siteforeman, was tamping down gunpowder in ablast hole with a 1-metre-long iron rod when

the powder exploded, propelling the rodstraight through his head. It entered justunder his left eyebrow and exited through thetop of his skull, before landing 20 metresaway. Miraculously, Gage recovered, but as hisphysician Harlow noted,“he was no longerGage”54. The previously amiable and efficientman had become someone for whom the“balance, so to speak, between his intellectualfaculties and his animal propensities seems tohave been destroyed.” He was now irreverent,impatient, quick to anger and unreliable.

The radical changes in personality andemotional behaviour of Gage represent anearly human lesion study of the effects of PFCdamage on emotions. Since Gage’s time, thePFC has been implicated in emotion in manyways, but there is no consensus as to its exactfunctions. In this section, I consider threecontemporary views of PFC functioning andtheir historical antecedents.

The PFC and reward processing. Rolls’s workon the orbitofrontal region of the PFC55–57

proposes that it is “involved in learning the emotional and motivational value ofstimuli”56. Specifically, he suggests that PFCregions work together with the amygdala tolearn and represent relationships between newstimuli (secondary reinforcers) and primaryreinforcers such as food, drink and sex.Importantly, according to Rolls, neurons in the PFC can detect changes or reversals in thereward value of learned stimuli and changetheir responses accordingly. These ideas havebeen based on 30 years of electrophysiological

Ventral pallidumHypothalamus

Cingulatecortex

Forebrain

Brainstem

(Dorsomedial)

Prefrontalcortex

(Orbital-ventromedial)

Accumbens

Amygdala

Figure 4 | Key structures within a generalized emotional brain. The figure does not show the relativedepths of the various structures, merely their two-dimensional location within the brain schematic. As thisis a lateral view, only one member of bilateral pairs of structures can be seen. Anatomical image adapted,with permission, from REF. 123 (1996) Appleton & Lange.



the hypothalamus in motivations such as sexand hunger87,88.

How many emotion systems?How do the different brain regions that havebeen implicated in emotion interact with eachother? What are the emotion systems in thebrain? Theories of how the functional neuro-anatomy of emotion operates systemicallyrange from single-system models, in which thesame neural system underlies all emotions, toviews that propose a combination of somecommon brain systems across all emotions,allied with separable regions that are dedicatedmore closely to the processing of certain indi-vidual emotions such as fear, disgust and anger(multiple-system models).

Single-system models. The proposals ofCannon and Bard, Papez (FIG. 2), MacLean(FIG. 3) and, to some extent, Damasio, are all examples of single-system models. A fur-ther example, alluded to in the discussion of Davidson’s work above71, is the ‘right-hemisphere hypothesis’, which was originallyproposed by Mills in 1912 (REF. 89) and ex-panded by Sackeim and Gur90,91 and others92,93.In its simplest form, this hypothesis empha-sized a specialized role of the right hemispherein all aspects of emotion processing90,91,though more refined views have proposedthat hemispheric specialization is restricted tothe perception and expression of emotion,rather than its experience94.

Dual-system models. Davidson’s valence asym-metry model is related to the right-hemispherehypothesis, with the emphasis in this casebeing on differential contributions of the leftand right hemispheres to positive and negativeemotions, respectively70,71. Other dual-systemtheorists, beginning with Schneirla in 1959(REF. 95), have proposed that the emotions canbe broken down into approach and withdrawalcomponents, and have used different terminol-ogy and proposed different neuroanatomicalsubstrates for each component; for example,behavioural activation and behavioural inhibition systems96,97, approach and with-drawal systems73, and appetitive and aversivesystems98. Finally, Rolls proposed a dual-systemapproach that conceptualizes emotions interms of states elicited by positive (rewarding)and negative (punishing) instrumental reinforcers, within a dimensional space56,57.

Multiple-systems models. Other theorists,inspired by the prototypical work of Darwin2,have proposed that a small set of discrete emo-tions are underpinned by relatively separableneural systems in the brain18,99–103. Some of the

The ACCContemporary affective neuroscientists viewthe ACC as a point of integration of visceral,attentional and emotional information that iscrucially involved in the regulation of affectand other forms of top–down control76,77. Ithas also been suggested that the ACC is a keysubstrate of conscious emotion experience78

(as suggested by Papez) and of the centralrepresentation of autonomic arousal79.

The ACC has generally been conceptual-ized in terms of a dorsal ‘cognitive’ subdivisionand a more rostral, ventral ‘affective’ subdivi-sion76. The affective subdivision of the ACC is routinely activated in functional imagingstudies involving all types of emotionalstimuli76,80,81. Current thinking suggests that itmonitors conflict between the functional stateof the organism and any new information thathas potential affective or motivational con-sequences. When such conflicts are detected,the ACC projects information about the con-flict to areas of the PFC where adjudicationsamong response options can occur76.

The hypothalamusIn the 1920s,Walter Hess conducted a series ofexperiments in which he implanted electrodesinto the hypothalamic region of cats82.Electrical stimulation of one part of the hypo-thalamus led to an ‘affective defence reaction’that was associated with increased heart rate,alertness and a propensity to attack. Hess couldinduce animals to act angry, fearful, curious orlethargic as a function of which brain regionswere stimulated. These results showed that asimple train of electrical impulses can bringabout a coordinated, sophisticated and recog-nizable emotional response. Furthermore, theresponse is not stereotyped but can be made ina skilfully targeted manner. In addition, differ-ent brain regions seemed to be associated withpleasure–approach and distress–avoidanceresponses.

Olds and Milner in 1954 (REF. 83)

performed electrical stimulation studies inrats to show that the hypothalamus was alsoinvolved in the processing of rewardingstimuli. The rats would press a lever to deliverelectrical ‘self-stimulation’ to the hypo-thalamus continuously for 75% of the timefor up to 4 hours a day. Similar argumentsconcerning the hypothalamus and rewardwere made by Heath in 1972 (REF. 84) in stud-ies investigating self-stimulation throughelectrodes in human subjects. The hypo-thalamus therefore seems to be part of anextensive reward network in the brain, alsoinvolving the PFC56, amygdala85 and ventralstriatum86. Numerous other electrical stimu-lation studies have identified further roles for

example, social situations). Nauta termed thisstate of affairs ‘interoceptive blindness’65. Theypropose that EVR cannot use somatic markersbecause of his ventromedial PFC damage and therefore tries, and fails, to deal with com-plex situations of uncertainty using logical reasoning alone.

In a famous study, Bechara, Damasio andcolleagues68 asked patients with ventromedialPFC damage (including EVR) to play a cardgame in which they could win or lose a rewardand for which they had to figure out the beststrategy as they went along. The trick to winning on the card task was to ignore theimmediate rewards on offer and become sensitive to the delayed rewards. Control par-ticipants could do this based on ‘hunches’,which they could not articulate, about whichcards to choose. Furthermore, these healthycontrols showed bodily responses (elevatedskin conductance) in anticipation of poorcard choices. By contrast, patients with dam-age to the ventromedial PFC did not learn toperform the task in this way and did not showthe skin conductance response. The argumentwas that for the healthy subjects, somaticmarkers develop in the early trials of the task,which then provide signals to guide later cardchoices68,69. The subjects were unaware ofthese signals but could act on them — makingintuitive or hunch decisions that ‘feel’ right.However, the patients lacked the brain regionsto process these somatic markers. They couldnot use such information and so could notperform the task.

The PFC and ‘top-down’ regulation. Davidsonand colleagues have proposed a different func-tion for the PFC. They argue that prefrontalregions (as well as the ACC, see below) send‘bias signals’ to other parts of the brain to guidebehaviour towards the most adaptive currentgoals70–74. Often behavioural choices are indanger of being heavily influenced by theimmediate affective consequences of a situa-tion (for example, immediate reward), eventhough the most adaptive response might be,for example, to delay gratification (not unlikethe optimal behaviour required on the Becharagambling task described above). Davidson andcolleagues suggest that the PFC promotesadaptive goals in the face of strong competitionfrom behavioural alternatives that are linked toimmediate emotional consequences75. In thismodel, left-sided PFC regions are involved inapproach-related appetitive (positive) goalsand right-sided PFC regions are involved in themaintenance of goals that require behaviouralinhibition and withdrawal (negative). This‘valence-asymmetry hypothesis’ is discussed inmore detail below.



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key research in support of this multi-systemview has come from human lesion studies andfrom functional neuroimaging. I have men-tioned a number of studies that have linkedthe processing of fear to the amyg-dala28,30,33,46,104,105. Similar studies are beginningto emerge with respect to disgust. Phillips andcolleagues used fMRI to show that perceptionof facial expressions of disgust was associatedwith activation in the anterior insularcortex106. This is consistent with early work byPenfield and Faulk in 1955 (REF. 107) that indi-cated that electrical stimulation of the insulain humans produced sensations of nausea andunpleasant tastes and sensations in the stom-ach. Following this up, Calder and colleaguesreported a patient with left hemisphere dam-age affecting the insula and basal ganglia,including the striatum. The patient showed aclear selective impairment in recognizing bothfacial and vocal signals of disgust, andimpaired experience of disgust108. Similarfindings have been reported in patients withHuntington’s disease109 — a condition thataffects the insula and the striatum — and incarriers of the Huntington’s disease gene110.There has been relatively little work on theneural substrates of other emotions111,112, andrecent meta-analyses show that the clearestsupport is for separable neural substrates forfear and disgust, focusing on the amygdalaand insula, respectively80,81, with other brainregions, notably the PFC and ACC, being activated for all emotions (see above).

The future of affective neuroscienceA historical analysis of the development ofaffective neuroscience reveals that many morebrain regions than initially supposed areinvolved in the processing of emotion and mood. In many ways this mirrors developments at the psychological level ofexplanation, where there is an increasingunderstanding of the pervasive influence ofemotions on all forms of psychological pro-cessing. An impressive body of knowledge isaccumulating about the roles of individualregions of the brain, such as the amygdala, inemotion processing. However, there is lessconsistency, and little hard empirical data,about the detailed interactions of theseregions as part of a broader emotion system.A key challenge for the future is to addressthese issues.

Related to this is the challenge of integrat-ing psychological models of emotion withneuroscientific models. At the psychologicallevel of explanation, there are multiple routesto the generation of emotion — some reflect-ing ‘automatic’ or conditioned emotionalresponses, and some representing emotions

derived from online appraisals of current circumstances113–115. There is a relative paucityof discussion and research on the underlyingneural basis of appraisal-driven emotions, andthis is an important research question if anyrapprochement between neural and psycho-logical levels of explanation is to be achieved.

The conscious experience of emotion is acrucial feature and has been the focus of arecent influential theoretical paper by Lambieand Marcel116,117. There has been little theoryor research on the underlying neural substrates of emotion experience, with theexception of the work of Richard Lane78, andthis is likely to be a focus of future efforts.

Future progress in affective neurosciencewill depend on the emergence of new technologies and methods. The advent offunctional brain imaging has transformed thefield in the last 10 years, and new forms ofimaging such as diffusion tensor imaging,which enables non-invasive tracing of whitematter tracts, will lead to further leaps in ourunderstanding. Another recent methodologywith enormous potential is transcranial mag-netic stimulation (TMS) — a technique thatenables a researcher or clinician to temporarilyand non-invasively activate or deactivate specific regions of cortex and to observe the behavioural or neural consequences inhumans. These advances will be comple-mented by more research that uses multiplemethodologies, integrating functional imag-ing, pharmacology, TMS, psychophysiology,cognitive psychology and the emerging field ofbehavioural genetics118.

The main focus of this review has been onso-called ‘normal’ emotions. However, there isan increasing interest in the neural substratesof abnormal emotional states119 and ofpsychiatric disorders such as depression120, aswell as the neural correlates of individual differences in normal emotions, for example,variations in ‘affective style’72. These issues willsurely come further into the spotlight in thedecades to come.

Tim Dalgleish is at the Emotion Research Group,Medical Research Council Cognition and

Brain Sciences Unit, 15 Chaucer Road,Cambridge, CB2 2EF, UK.

e-mail: [email protected]

doi:10.1038/nrn1432

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AcknowledgementsI would like to acknowledge A. Lawrence for advice and commentsthroughout the preparation of this manuscript. This work wasfunded by the UK Medical Research Council.

Competing interests statementThe author declares that he has no competing financial interests.

Online links

FURTHER INFORMATIONDalgleish’s homepage: http://www.mrc-cbu.cam.ac.uk/personal/tim.dalgleish/Access to this interactive links box is free online.

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