J.A. Gray's Reinforcement Sensitivity Theory (RST) of Personality

J.A. Gray’s ReinforcementSensitivity Theory (RST)

of Personality

Alan Pickering and Philip Corr

Jeffrey Gray’s (1976, 1982) behavioural inhibition system (BIS) theory of anxiety hasstood well the test of time. This theory ofpersonality – which is now widely known asreinforcement sensitivity theory (RST) – hasgradually evolved over the past 30 years,seeing its major revision in 2000 by Gray andMcNaughton, and even further elaborationsand refinements subsequently (McNaughtonand Corr, 2004, 2008; Corr and McNaughton,2008). However, recent data that havestrengthened the general foundations of theneural basis of the theory have also forcedsignificant modifications of, and additions to,its superstructure. These changes are notinconsequential; as such, predictions cannotnow be based on prior knowledge of the 1982version. These changes, we contend, have thepotential to lead to confusion. A major purpose of this chapter is to review the currentscientific status of Gray’s RST and draw outsome of its major implications for futureresearch.

RST is built upon a state description ofneural systems and associated, relatively

short-term, emotions and behaviours, which,according to the theory, give rise to longer-term trait dispositions of emotion and behaviour. This theory argues that statisticallydefined personality factors are sources ofvariation that are stable over time and that derive from underlying properties of anindividual; it is these, and current changes inthe environment, that comprise the neuropsy-chological foundations of ‘personality’. Thisassertion is demanded by the fact that personality traits account for behavioural differences between individuals presentedwith identical environments; also, behaviouraldifferences show consistency across time.Thus, the ultimate goal of personalityresearch is to identify the relatively static(underlying) biological variables that determinethe (superficial) factor structure measured inbehaviour. It would, of course, be a mistaketo deny the relevance of the environment incontrolling behaviour, but to produce consis-tent long-term effects, environmental influ-ences must be mediated by, and instantiatedin, biological systems.

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Gray’s approach to the biological basis of personality followed a particular pattern:(a) first identify the fundamental propertiesof brain-behavioural systems that might beinvolved in the important sources of variationobserved in human behaviour and (b) thenrelate variations in these systems to knownmeasures of personality. Central to thisapproach is the assumption that the variationobserved in the functioning of these brain-behavioural systems comprise what we term‘personality’. As discussed below, relating(a) to (b) has proved the major challenge toRST researchers.

Now, most RST studies have tested theunrevised (pre-2000) version of RST. But, aswe shall see, in many crucial respects, therevised Gray and NcNaughton (2000) theoryof the underlying neural systems and theirfunction is very different, leading to the for-mulation of new personality hypotheses,some of which stand in opposition to thosegenerated from the unrevised theory (for moredetailed discussion of these matters, see Corr,2004, 2008; Corr and McNaughton, 2008;McNaughton and Corr, 2004, 2008).

‘CLASSIC’ (1970–2000) AND REVISED (2000–) REINFORCEMENTSENSITIVITY THEORY

Today, in personality research, it is commonto relate personality factors to emotion andmotivational systems, but this consensus didnot prevail before the time of Gray’s originalwork. It is a mark of achievement that Gray’s(1970, 1982) approach is today so widelyaccepted, and the emergence of a neuro-science of personality can be seen to belargely shaped by his work. In a similar veinto Hans Eysenck’s (1957, 1967) theoriesbefore him, Gray’s innovation was to puttogether the existing pieces of the scientificjigsaw in order to provide the foundations of a general theory of personality. Gray, like Pavlov (1927) before him, advocated atwin-track approach: the conceptual nervous

system (cns), and the central nervous system(CNS) (cf. Hebb, 1955). That is, the cnscomponents of personality (e.g. learningtheory; see Gray, 1975) and the componentbrain systems underlying systematic varia-tions in behaviour (ex hypothesi, personal-ity). As noted by Gray (1972a), these twolevels of explanation must be compatible, butgiven a state of imperfect knowledge itwould be unwise to abandon one approach infavour of the other. Gray used the languageof cybernetics, in the form of cns–CNSbridge, to show how the flow of informationand control of outputs is achieved (e.g. theGray and Smith, 1969, ‘arousal-decision’model).

Theoretical origins of RST

In contrast to Gray’s bottom-up generalapproach, Hans Eysenck adopted a very different ‘top-down’ method. His search forcausal systems was determined by the structure of statistically derived personalityfactors/dimensions. In an important respect,Eysenck’s approach was viable: this was tounderstand the causal bases of observedpersonality structure, defined as a unitarywhole (e.g. extraversion and neuroticism).For this very reason, it is perhaps not surpris-ing to learn that Eysenck’s causal systemsnever developed beyond the postulation of asmall number of very general brainprocesses, principally the ascending reticularactivating system (ARAS), underlying thedimension of introversion–extraversion andcortical arousal (for a summary see Corr,2004). A second dimension, neuroticism (N),was related to activation of the limbic systemand emotional instability (see Eysenck andEysenck, 1985). Taken together, Gray’s andEysenck’s approaches are complementary,tackling important problems at differentlevels of analysis.

Eysenck’s (1967) arousal theory of extra-version hypothesized that introverts andextraverts differ with respect to the sensitivityof their cortical arousal system; and this is in

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consequence of differences in responsethresholds of their ARAS. According to thistheory, compared with extraverts, introvertshave lower response thresholds and thushigher cortical arousal. In general, introvertswere said to be more cortically aroused andmore arousable when faced with sensorystimulation. However, the extraversion-arousal champions marched under a bannerupon which was blazoned an inverted-Usymbol – chosen, in large measure, by virtueof the Pavlovian notion of transmarginalinhibition (TMI; a protective mechanism thatbreaks the link between increasing stimuliintensity and behaviour at high intensitylevels – in the Hullian learning literature this effect went under the name of ‘stimulusintensity dynamism’). It was against this theoretical backdrop that RST developed.

Gray’s (1970, 1972b, 1981) modificationof Eysenck’s theory proposed changes: (a) tothe position of extraversion (E) and neuroticism

(N) in Eysenckian factor space; and (b) totheir neuropsychological bases. Gray arguedthat E and N should be rotated by approxi-mately 30 degrees to form the more causallyefficient axes of ‘punishment sensitivity’,reflecting anxiety (Anx), and ‘reward sensitivity’, reflecting impulsivity (Imp)(Figure 11.1; see Pickering et al., 1999).

This modification stated that Imp + indi-viduals are more sensitive to signals ofreward, relative to Imp− individuals, andAnx+ individuals are more sensitive to signals of punishment, relative to Anx− indi-viduals. The proposed independence of theaxes suggested that (a) responses to rewardshould be the same at all levels of Anx and(b) responses to punishment should be thesame at all levels of Imp – this position wasdubbed the ‘separable subsystems hypothesis’by Corr (2001, 2002). According to RST,Eysenck’s E and N dimensions are derivativesecondary factors of these more fundamental

J.A. GRAY’S REINFORCEMENT SENSITIVITY THEORY (RST) OF PERSONALITY 241

ExtraversionIntroversion

Neuroticism

Stability

BASREW: Reward sensitivity‘impulsivity’

FFFS(BIS)PUN: Punishment sensitivity‘anxiety’

Figure 11.1 Position in factor space of the fundamental punishment sensitivity and rewardsensitivity (unbroken lines) and the emergent surface expressions of these sensitivities, viz.extraversion (E) and neuroticism (N) (broken lines). The current working hypothesis is that‘punishment sensitivity’ – which, in the unrevised model, was labelled ‘anxiety – relates to both the FFFS and BIS’

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punishment and reward sensitivities: E reflectsthe balance of punishment and reward sensitivities; N reflects their joint strengths(Gray, 1981).

Clinical neurosis

Eysenck’s taxonomic model of personalitywas based on the factor analysis of the symptoms of war ‘neurotics’ (1944, 1947),and his 1957 and 1967 causal theories weredesigned to explain the genesis of these neuroses; it is, thus, on these grounds that the theory is critically tested. In brief,Eysenck postulated that introverts are moreprone to suffer from anxiety disorders byvirtue of their greater conditionability, especially of emotional responses. Thistheory was later elaborated to include thenotion of incubation effects in conditioning(Eysenck, 1979), in order to account for the ‘neurotic paradox’ (i.e. the failure ofextinction with continued non-reinforcementof the CS). Coupled with emotional instability,reflected in N, this made the introverted neurotic (E−/N+) particularly prone to anxiety disorders.

However, from the very beginning of thisarousal-based theory of personality, anumber of problems refused to be silenced.For one, introverts show weaker classicalconditioning under conditions conducive tohigh arousal (which, we must assume, is alsoinduced by aversive UCSs), as seen in eyeblink conditioning studies (Eysenck and Levey, 1967). This finding supportsEysenck’s own theory that introverts aretransmarginally inhibited by high arousal,but at the very same moment fails to explainadequately the genesis of clinical neurosis.Other problems also screamed out to beheard. For example, impulsivity (inclinedinto the N plane; see Figure 11.1), not socia-bility (defining the extraversion axis), isoften found to be associated with condition-ing effects (Eysenck and Levey, 1972), butthis places high arousability, and thus high

conditionability, along an axis that is orthogonal to the one which has its high pole in the neurotic-introvert quadrant where clinical neurosis is located. Thus,Eysenck’s own theory seems unable toexplain the development of anxiety in neu-rotic-introverts. Time-of-day effects further undermine the central postulates ofEysenck’s personality theory of clinical neurosis (see Gray, 1981).

In addition to the above problems, Graycited a further reason to prefer a non-conditioning explanation (Corr, 2008). Now,classical conditioning theory states that as a result of the conditioned stimulus (CS) and unconditioned stimulus (UCS) beingsystematically paired, the CS comes to takeon many of the eliciting properties of theUCS. That is, when presented alone afterconditioning, the CS produces a response(i.e. the conditioned response, CR) thatresembles the unconditioned response(UCR) elicited by the UCS. However, the CRdoes not substitute for the UCR – in severalimportant respects, the CR does not evenresemble the UCR. For example, a pain UCS will elicit a wide variety of reactions(e.g. vocalization and behavioural excite-ment) which are quite different to thoseelicited by a CS signalling pain, which con-sists of a quite different set of behaviours(e.g. quietness and behavioural inhibition).We thus have a theory that does not seem fitfor purpose: classical conditioning cannotexplain the pathogenesis or phenomenologyof neurosis, although it can explain how initially neutral stimuli (CSs) acquire themotivational power to elicit this state. Grayasked the crucial question: if classical conditioning does not account for the gener-ation of the negative emotional state thatcharacterises neurosis, then what does? Hisanswer – based upon extensive animalresearch (e.g. behavioural, pharmacological,lesion, and electrical stimulation studies) –was an innate mechanism, namely the behavioural inhibition system (BIS; Gray,1976, 1982).


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Three systems of ‘classic’ RST

RST gradually developed over the years toinclude three major systems of emotion:

1 The behavioural inhibition system (BIS) was postulated to be sensitive to conditioned aversivestimuli (i.e. signals of both punishment and the omission/termination of reward) relating toAnx, but also to extreme novelty, high-intensitystimuli, and innate fear stimuli (e.g. snakes, blood),which are more related to fear.

In addition, two other systems were postulated:

2 The fight / flight system (FFS) was postulated to be sensitive to unconditioned aversive stimuli (i.e. innately painful stimuli), mediating the emo-tions of rage and panic. This system was relatedto the state of negative affect (NA) (associatedwith pain) and speculatively associated by Graywith Eysenck’s trait of psychoticism.

3 The behavioural approach system (BAS) was postulated to be sensitive to conditioned appetitivestimuli, forming a positive feedback loop, activatedby the presentation of stimuli associated withreward and the termination/omission of signalsof punishment. This system was related to thestate of positive affect (PA) and the trait of Imp.

The BIS was modelled on the detailed patternof behavioural effects of classes of drugsknown to affect anxiety in human beings. Bythis route, Gray argued, anxiety could beoperationally specified as those behaviourschanged by anxiolytic drugs. Of course, thereexists here the danger of circularity of argument; this was avoided by the postula-tion that anxiolytic drugs do not simplyreduce anxiety (itself a vacuous tautology),but could be shown to have a number ofbehavioural effects in typical animal learningparadigms. Experimental evidence showedthat anti-anxiety drugs affected responses toconditioned aversive stimuli, the omission ofexpected reward and conditioned frustration,all of which Gray postulated were mediated bya BIS, which was responsible for suppressing

ongoing operant behaviour in the face ofthreat, as well as enhancing information processing and vigilance. (We shall see thatin this revised theory, these effects can bereclassified as conflict effects.) Later, theBAS was added to account for behaviouralreactions to rewarding stimuli – these werelargely unaffected by anti-anxiety drugs. Thedanger of a circularity of argument was further reduced by the behavioural profile ofthe newer classes of anxiolytics which, itturned out, had the same behavioural effectsand acted on the same neural systems as theolder class of drugs, despite the fact that they had different psychopharmacologicalmodes of action and side-effects (Gray andMcNaughton, 2000).

Revised (2000–) RST

The Gray and McNaughton (2000) revisedtheory updates and extends the ‘classic’version. These changes are, in parts, substantial:but, in other parts, more a clarification of the1982 theory. Revised RST postulates threesystems.

1 The fight–flight–freeze system (FFFS) is responsi-ble for mediating reactions to aversive stimuli ofall kinds, conditioned and unconditioned. It fur-ther proposes that there exists a hierarchicalarray of neural modules, responsible for avoid-ance and escape behaviours. Now, the FFFS medi-ates the emotion of fear, not anxiety. Theassociated personality factor comprises fear-proneness and avoidance, which is clinicallymapped onto such disorders as phobia and panic.

2 The BAS mediates reactions to all appetitive stim-uli, conditioned and unconditioned. This systemgenerates the appetitively hopeful emotion of‘anticipatory pleasure’, and hope itself. The asso-ciated personality comprises optimism, reward-orientation and impulsiveness, which clinicallymaps onto addictive behaviours (e.g. pathologi-cal gambling) and various varieties of high-risk,impulsive behaviour, and possibly the appetitivecomponent of mania. The BAS is largelyunchanged in the revised Gray and McNaughtonversion of RST.


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3 The BIS is responsible, not, as in the 1982 version,for mediating reactions to conditioned aversivestimuli and the special class of innate fear stimuli, but for the resolution of goal conflict ingeneral (e.g. between BAS-approach and FFFS-avoidance, as in foraging situations – but it isalso involved in BAS–BAS and FFFS–FFFS conflicts).The BIS generates the emotion of anxiety, whichentails the inhibition of prepotent conflictingbehaviours, the engagement of risk assessmentprocesses, and the scanning of memory and the environment to help resolve concurrent goal conflict.

The BIS resolves conflicts by increasing,through recursive loops, the negative valenceof stimuli (these are adequate inputs into the FFFS), until behavioural resolutionoccurs in favour of approach or avoidance.Subjectively, this state is experienced as worryand rumination. The associated personalitycomprises worry-proneness and anxiousrumination, leading to being constantly on thelook-out for possible signs of danger, whichmap clinically onto such conditions as gener-alized anxiety and obsessional-compulsivedisorder (OCD). There is an optimal level ofBIS activation: too little leads to risk seeking(e.g. psychopathy) and too much to risk aversion (generalized anxiety), both reflectingsuboptimal conflict resolution.

NEUROPSYCHOLOGICAL STRUCTUREOF THE REVISED THEORY

Revised RST agrees with the classical versionin its assertion that substantive affectiveevents fall into just two distinct majorclasses: positive and negative (Gray, 1975;Gray, 1982; Gray and McNaughton, 2000).Rewards and punishments are the obviousexemplars of positive and negative events,respectively. But, importantly for humanexperiments, the absence of an expected pos-itive event is functionally the same as thepresence of a negative event and vice-versa(Gray, 1975). Omission of expected reward isthus punishing. Similarly, the absence of an

expected negative event is functionally thesame as the presence of a positive event.Omission of punishment is rewarding. Thisbasic scheme gives rise to a two-dimensionalmodel of the neuropsychology of emotion,motivation, and personality that simplifies thetheory, as well as serving as a point of unifi-cation of the otherwise complex arrangementof the separate neural modules underlyingbehaviour (McNaughton and Corr, 2004).

Fear and anxiety – defensive direction

The first dimension, ‘defensive direction’, iscategorical. It rests on a functional distinctionbetween behaviours that remove an animalfrom a source of danger (FFFS-mediated)and those that allow it cautiously to approacha source of potential danger (BIS-mediated).These functions are ethologically and phar-macologically distinct and, on each of theseseparate grounds, can be identified with fearand anxiety, respectively. The revised theorytreats fear and anxiety as not only quite distinct but also, in a sense, as opposites. The categorical separation of fear from anxiety as classes of defensive responses hasbeen demonstrated by Robert and CarolineBlanchard (Blanchard and Blanchard, 1988,1990; Blanchard et al., 1997).

The Blanchards used ‘ethoexperimentalanalysis’ of the innate reactions of rats to catsto determine the functions of specific classesof behaviour. One class of behaviours waselicited by the immediate presence of a pred-ator. This class could clearly be attributed toa state of fear. The behaviours, grouped intothe class on purely ethological grounds, weresensitive to panicolytic drugs but not to drugs that are specifically anxiolytic. This isconsistent with the insensitivity to anxiolyticdrugs of active avoidance in a wide variety ofspecies, and phobia in humans is also insen-sitive to anxiolytic drug treatment (Sartory et al., 1990). A second, quite distinct, class ofbehaviours (including ‘risk assessment’) waselicited by the potential presence of a predator.


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This class of behaviours was sensitive to anxiolytic drugs. Both functionally andpharmacologically, this class was distinctfrom the behaviours attributed to fear andcould be attributed to a state of anxiety.

Fear and anxiety – defensive distance

The second dimension, ‘defensive distance’,is graded: it rests on a functional hierarchythat determines appropriate behaviour inrelation to defensive distance (i.e. perceiveddistance from threat). This second dimensionapplies equally to fear and anxiety but isinstantiated separately in each.

Defensive distance equates with real distance; but in a more dangerous situation,the perceived defensive distance is shortened.In other words, defensive behaviour (e.g. activeavoidance) will be elicited at a longer (objective) distance with a highly dangerousstimulus (which shortens perceived defensivedistance), as compared to the elicitation ofdefensive behaviour by a less dangerousstimulus. According to the theory, certainindividuals have a much shorter perceiveddefensive distance for a given threat stimulus,and thus react more intensively to relativelyinnocuous (in real distance terms) stimuli.

McNaughton and Corr (2004) view individual differences in defensive distancefor a fixed real distance as a reflection of the personality dimension underlying ‘pun-ishment sensitivity’, or ‘threat perception’.They suggest that the high pole of thisdimension is neurotic-introversion and thelow pole is stable-extraversion. This personal-ity dimension affects the FFFS-mediatedbehaviours directly, but affects those medi-ated by the BIS only indirectly (e.g. viaFFFS-BAS goal conflict). Anxiolytic drugsare argued to alter (internally perceived)defensive distance relative to actual externalthreat. They do not affect defensive behav-iour directly, but rather operate to shiftbehaviour along the defensive axis, often leading to the output of a different

behaviour (e.g. risk-assessment to pre-threatbehaviour).

An important conclusion of this theory,which goes to show the subtlety of revisedRST, is the claim that the comparison of indi-viduals on a single measure of performanceat only a single level of threat may produceresults that are difficult to interpret. Forexample, for an objectively defined defensivedistance, one person may be in a state ofpanic and so cease moving, while anothermay actively avoid and so increase theirmovement. That is, highly sensitive andinsensitive fearful individuals will show dif-ferent behaviours at the same level of threat(defined in objective terms), as indeed willtrait-identical individuals at different levelsof threat. Thus moving people along this axisof defensive distance (by drugs or by experi-mental means) will not simply affect thestrength or probability of a given behaviour,but is expected to result in different behav-iours (which, themselves, may be in opposi-tion). As we can see, at the core of the revisedtheory are ethological factors, relating specificbehaviours to specific threats and environ-mental conditions.

Conflict

Revised RST defines anxiety in terms ofdefensive approach. However, this notioncontains something more fundamental about anxiety, namely, conflict. An animalapproaches a threat only if there is some possibility of a positive outcome (e.g. foodwhen foraging in an unsafe field). But threatsare not the only sources of aversion andavoidance encountered. In principle, approach–approach and avoidance–avoidance conflictsalso involve activation of the same systemand have essentially the same effects as classic approach–avoidance. It turns out thatthe conditioned stimuli to which the unrevisedversion of the BIS was said to be sensitiveare, according to this formulation, specificexamples of conflict stimuli. Thus, the newBIS theory reclassifies conditioned stimuli


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and expands the type of stimuli processed by the BIS. All of these now fall under thecommon rubric of goal conflict. This refor-mulation also helps tidy-up the rag-bag ofother eliciting stimuli of the BIS (i.e. innatestimuli and high-intensity noise): in theirnon-conflict form, they now belong with the FFFS.

NEURAL SYSTEMS OF FEAR AND ANXIETY

Revised RST combines a large number ofbrain structures ranging from the prefrontalcortex, at the highest level, to the periaque-ductal grey, at the lowest level, assigning toeach structure: (a) a specific place in thetheory; (b) a specific fundamental class offunction; and (c) a specific class of mentaldisorder (McNaughton and Corr, 2008).Thus, the most fundamental change to theold view of the BIS is that it is distributedamong a number of neural structures.

General architecture

The concepts of defensive direction anddefensive distance provide a two-dimensionalschema within which all defensive behaviourscan be described. The theory translates thistwo-dimensional psychological schema intoa matching two-dimensional neurologicalone. In particular, the categorical distinctionbetween defensive approach and defensiveavoidance is translated into two distinct parallel streams of neural structures; and the dimension of defensive distance is translated into the levels of a hierarchy ofstructures within each of the parallel streams(Figure 11.2).

The neural mapping of defensive distanceinto the two hierarchies is rendered simple bytwo architectural features. First, smallerdefensive distances map to more caudal, sub-cortical neural structures while larger defen-sive distances map to more rostral, cortical

neural structures with intermediate structuresarranged in caudo-rostral order in between.Second, this mapping occurs in a symmetri-cal fashion with matching structures locatedwithin each of the parallel streams (this ofteninvolves subdivisions, or nuclei, of the samenamed area).

THE BEHAVIOURAL APPROACHSYSTEM (BAS)

We now have an outline of the FFFS and thematching components of the BIS. RevisedRST theory also has a central place for theBAS. It must be borne in mind that, althoughthe BIS would be activated with the simulta-neous activation of the FFFS and the BAS(e.g. in the case of approach–avoidance conflict), it remains the case that the BAS is conceptually distinct from both the BISand the FFFS.

Neural organization of the BAS

There are tensions in attempts to map theBAS onto brain systems and functions. Aswith the BIS and the FFFS, the BAS can beviewed as hierarchically organized. Gray(Gray and McNaughton, 1996; Gray et al.,1991) has described the BAS as having a ‘caudate’ component and an ‘accumbens’component. However, he also made clear that‘accumbens holds a list of subgoals makingup a given motor program and is able toswitch through the list in an appropriateorder, but to retrieve the specific content ofeach step, it needs to call up the appropriatesubroutine by way of its connections to the[caudate] system’ (Gray and McNaughton,1996). Such caudate motor command subroutines are quite distinct from the affect-laden goals that are the subject of theFFFS, BAS and BIS (Gray and McNaughton,2000).

On the other hand, as with the FFFS, thehierarchical organization of the BAS makes


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it difficult for any part of it to control overallBAS sensitivity. Where a personality factor isthought to alter such sensitivity generally, we should probably look for appropriatemodulatory systems. The neuromodulatorthat is probably of primary importance inBAS functioning is dopamine (DA; Depueand Collins, 1999; Pickering and Gray,1999). The accumbens and caudate separa-tion, alluded to by Gray, is reflected in the distinction between the so-called mesolimbicand nigrostriatal projection pathways ofdopaminergic cells (these project to accum-bens and caudate respectively, along with

other structures). However, many influences(e.g. genes), which could generate individualdifferences in dopaminergic neurotransmission,may well express their effects on more thanone dopaminergic projection system (Depueand Collins, 1999). Moreover, the structuresinnervated by these distinct dopaminergicsystems act cooperatively to deliver behav-ioural responses thought of as being underBAS control.

In the neuroscience literature, over the last 15 years or so, a strong consensus hasemerged over the functional significance offiring of dopaminergic cells in the midbrain


5HT

PREFRONTAL “GAD” -DORSAL STREAM drug-resistant

POSTERIOR GAD -CINGULATE cognition

SEPTO-HIPPO- GAD -CAMPAL SYSTEM cognition

Defensiveapproach:Anxiety

AMYGDALA GAD -arousal

PREFRONTAL - OCDVENTRAL STREAM

ANTERIOR OCDCINGULATE

AMYGDALA Phobia -avoid

MEDIAL Phobia -HYPOTHALAMUS escape

PERIAQUEDUCTAL Panic -GRAYexplode/freeze

Defensiveavoidance:Fear

AMYGDALA Phobia -arousal

Personality traits

Leaving dangeroussituation

Entering dangeroussituation

Defensive direction

Defensive distance

Figure 11.2 The two-dimensional defence system of fear and anxiety. On either side aredefensive avoidance and defensive approach, respectively (this is a categorical dimension of ‘defensive direction’). Each system is divided into a number of hierarchical levels (corresponding to the second dimension of ‘defensive distance’). These are ordered from high to low (top to bottom) both with respect to neural level (and cytoarchitectonic complexity) and to functional level. Each level is associated with specific classes of behaviour and so symptom and syndrome (as shown). General monoamine modulation isshown as the putative ‘personality’ influence that provides unity to each system

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(Arbuthnott and Wickens, 2007; Schultz,1998). The view is that DA cell firing reflectsa ‘reward prediction error’ (RPE) signal.Specifically, in primates, increased bursts ofDA cell firing result when an unexpected(under-predicted) reward occurs. Decreasesin DA cell firing are observed when anexpected reward does not occur (see Schultz,1998, for details). Neuroimaging evidence inhumans has also emerged which is consistentwith this view (e.g. Abler et al., 2006). Asargued elsewhere (Pickering and Gray, 1999,2001; Pickering and Smillie, 2008), a properneuroscientific understanding of the BASwill need to incorporate this RPE conceptu-alization of DA cell firing.

Of great interest in this area, the RPE viewof DA cell firing is consistent with classiccomputational models of reinforcementlearning (e.g. Dayan and Abbott, 2001).Learning in these models is hypotheticallycontrolled by an RPE signal: a positive RPE(caused by an unexpected reward) is used tostrengthen learning in the neural pathwayswhich generated the behaviour leading to thereward; a large negative RPE (caused by anon-occurring expected reward) is used toextinguish learning in the neural pathwayswhich generated the behaviour leading to thereward. When the RPE is close to zero (i.e. thelevel of reward is accurately predicted), thenlittle learning takes place. The observationsthat DA cells fire in a fashion closely resembling an RPE signal was seen as providing a neural validation of these models.Moreover, the dopaminergic projection path-ways release dopamine at sites very close tosynapses on the dendritic spines of caudateand accumbens cells; these synapses are atthe terminals of cortical inputs to the stria-tum. This synaptic arrangement, and the den-dritic spines themselves, have a number ofneurophysiological features (Wickens andKotter, 1995) which enables an incomingburst of dopaminergic firing to operate effectively as a reinforcement/RPE signaland control learning at those cortico-striatalsynapses.

The RPE conceptualization of dopaminecell firing in projections to BAS structures(caudate, accumbens, etc.) has strong resonances with the Gray and Smith (1969)cybernetic model of the functional interactionsbetween the reward and punishment systems.In this model, the reward system had a comparator within it which determinedwhether the level of reward received matchedthe level expected. It was proposed that theresults of this comparison process were fedback appropriately as inputs to the rewardand punishment systems, although thedetailed way in which this controlled learn-ing of responses was not specified. The RPEaccount outlined above suggests how thislearning may be accomplished. The Gray andSmith (1969) model proposed a generalframework for choosing between responsesleading to rewarding versus punishing behav-ioural consequences. Recent theoreticalmodels of potential BAS structures in thebasal ganglia have formalized the way thatthey may allow efficient decision-making ofthis kind (for an overview and references, seeBogacz, 2007).

Previously, accounts have been offered tobegin to incorporate the neuroscience ofdopamine cells and the basal ganglia into ourunderstanding of the BAS (Pickering andGray, 1999, 2001; see also Pickering andSmillie, 2008). This research is proceedingapace, and the final details have yet to beworked out. A challenge will be able to findan appropriate level of modelling which isable to distinguish between alternative neurally based accounts of the BAS.

What personality trait is linked to the BAS?

What broad personality trait might correspondto variations in the functioning of the BAS?Gray’s original decision to call it ‘impulsivity’was entirely ad hoc, as he repeatedly admit-ted. He used the ancient circular model of thehumours (popularized by Eysenck) and drew


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a line between the types ‘anxious’ and ‘carefree’ (being confident that the BIS subserved trait anxiety). The line at rightangles to the anxiety dimension (he assumedthe BAS and BIS traits were orthogonal)approximately joins the labels of ‘impulsive’and ‘thoughtful’ (although he might as easilyhave chosen ‘optimistic’ and ‘careful’ onthese geometric grounds!). Thus, the impul-sivity dimension was born; although Grayalso had to decide which way round to placethe dimension (high BAS types wereassigned to the impulsive end of the dimen-sion, on grounds of plausibility). This deci-sion was further reinforced by the twocomponents of extraversion in Eysenck’smodel, namely sociability and impulsivity, as well as experimental work showing impul-sivity related to classical conditioning effects(see above).

On a related matter, Corr (2008) has drawnattention to the inadequate conceptualizationof the BAS, especially as it relates to impul-sivity. On evolutionary grounds, the BASmay be thought to be more complex than theFFFS, or indeed the BIS. The primary func-tion of the BAS is to move the animal up thetemporo-spatial gradient to the final biologi-cal reinforcer. This primary function is sup-ported by a number of secondary processes,comprising perhaps simple approach, perhapswith BIS activation exerting behavioural caution at critical points, designed to reducethe distance between current and desiredappetitive state (e.g. as seen in foragingbehaviour in a densely vegetated field).However, in human behaviour, this depictionof BAS-controlled approach behaviour maybe oversimplified.

First, it is helpful to distinguish the incentivemotivation component and the consummatorycomponent of reactions to appetitive stimuli.The neural machinery controlling reactionsto unconditioned (innate) stimuli, and itsassociated emotion, must be different fromthat controlling the behaviour and emotionassociated with approach, signalled by conditioned stimuli, to such stimuli. Thus, while

the BAS responds to all appetitive stimuli, itis concerned specifically with the appetitive-approach aspects that move the animalstowards the final biological reinforcer; at thispoint, non-BAS consummatory mechanisms,specific to the particular reinforcer con-cerned, are activated, e.g., the eating of food.

Second, moving to approach proper, wecan discern a number of relatively separate,albeit overlapping, processes. At the simplestlevel, there seems an obvious differencebetween the ‘interest’ and ‘drive’ that charac-terizes the early stages of approach, and thebehavioural and emotional excitement as theanimal reaches the final biological reinforcer.Emotion in the former case may be termed‘anticipatory pleasure’ (or ‘hope’); in thelatter, ‘excitement’. There is evidence that, atthe psychometric level, the BAS is multidi-mensional. For example, the Carver andWhite (1994) BIS/BAS scales measure threeaspects of BAS: reward responsiveness,drive, and fun-seeking. It may be speculatedthat drive is concerned with actively pursingdesired goals, reward-responsiveness is con-cerned with excitement at doing things welland winning, and fun-seeking is concernedwith the impulsivity aspect of the BAS (whichis especially appropriate for the capture ofthe final biological reinforcer).

Subgoal scaffolding

As discussed in detail by Corr (2008), BASbehaviour may best be seen as involving a series of appetitively motivated subgoals.That is, in order to move along the temporo-spatial gradient to the final primary biologi-cal reinforcer, it is necessary to engage insubgoal scaffolding. This process has severalstages: (a) identification of the biologicalreinforcer; (b) planning behaviour; and (c) executing the plan. Important in this regardis the following: complex approach behaviourentails a series of behavioural processes,some of which oppose each other. For example,behaviour restraint and planning are often


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demanded to achieve BAS goals, but not atthe final point of capture of the biologicalreinforcer, where non-planning and fast reac-tions (i.e. impulsivity) are more appropriate.Being a highly impulsive person – that is,acting fast without thinking and not planning– would not be appropriate BAS behaviour inanything other than very simple situations.Indeed, such behaviour would often movethe animal away from their desired goal. Forthis reason, and others mentioned above,‘impulsivity’ is not the most appropriate termfor the personality factor corresponding to thefull range of processes entailed by the BAS.

Therefore, given such a weak basis forGray’s initial labelling of the BAS, as well itsapparent complexity, it is somewhat surprisingthat the BAS has been equated with impul-sivity for so long. The first serious contradic-tory views came many years later. Depue andCollins (1999) argued that extraversion (and inparticular its agentic aspects) better capturedthe nature of the BAS-related personalitytrait. Their argument drew on detailed supportfrom the animal neurophysiological literaturebut was, in essence, a simple one. First, theysuggested that the BAS was closely linked todopaminergic neurotransmission. Second,they argued that the extant evidence pointedto a link between extraversion and dopamin-ergic neurotransmission which was strongerthan the link for any other major personalitytrait. We (Corr, 1999; Pickering, 1999;Pickering and Gray, 1999) cautioned that theevidential basis for part two of their argumentrested on a tiny body of data, mostly fromDepue and colleagues’ own laboratory. Inaddition, we suggested that Depue andCollins had ignored an equally small body of data which pointed to links betweendopaminergic neurotransmission and a cluster of traits we have termed impulsiveantisocial sensation seeking (ImpASS),rather than extraversion. At that time we feltthat the jury could not reach as clear a verdictas that reached by Depue and Collins andargued that (aspects of) the ImpASS traitcluster might correspond to the BAS trait.Subsequent neuroscience data has emerged

that is broadly in line with Depue and Collins’thesis (e.g. Cohen et al., 2005; Wacker et al.,2006). However, there are also psychometricand behavioural data (see Smillie et al., 2006,for a review) which we feel now tip the scalesmore strongly in favour of the idea that extra-version might be the BAS trait. But, furtherdata are needed, especially ones relating spe-cific psychometric measures of the revisedRST’s systems to extraversion.

INTERACTIONS OF THE BAS, FFFS,AND BIS: IMPLICATIONS FOR TRAITMEASUREMENT

The old description of RST supposed thateach system had a reactivity/sensitivity to itskey inputs, which we can denote wA, wI, andwF for the sensitivity of the BAS, BIS, andFFFS, respectively. Interindividual variationsin wA, wI, and wF are assumed to follow anormal distribution with each sensitivityindependent of (uncorrelated with) theothers. The trait of anxiety, Anx, was taken to reflect variation in wI and another trait(‘the BAS trait’) was taken to reflect variation in wA.

Elsewhere we (Corr, 2002; Pickering,1997) argued that the effects of such systemson behaviour would generally not be independent of one another even though thesensitivities were themselves independent –although, under certain conditions, theywould (specified by Corr, 2002). Thus, forexample, a behaviour controlled by rewardreinforcers would not only be influenced bythe BAS personality trait (i.e. wA) but couldalso often be influenced by Anx. Corr (2002) dubbed this the joint subsystemshypothesis in contrast to an earlier view thatbehaviour controlled by reward woulddepend selectively upon wA (the separablesubsystems hypothesis).

Recently, Smillie et al. (2006) took thisview further. They argued that self-reportquestionnaire responses, used to measure per-sonality traits, are likely to reflect subjective


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estimates of the functional outcomes ratherthan latent properties of the individual neuralsystems. A functional outcome of the BASmight be its mean output level across a rangeof situations, whereas a latent propertywould be its sensitivity (wA). They suggestedthat the functional outcome will be availablefor introspection (and hence self-report)whereas a sensitivity will not, although thesensitivities will clearly have a direct influ-ence on the observable functional outcome(someone with a higher value of wA will, allother things being equal, have a higher meanBAS output level than a person with lowerwA). Looking at the item content of variouspossible BAS personality trait measures,Pickering (2008) concluded that such ques-tionnaires might well reflect functional BASoutcomes (such as mean output level).

This viewpoint leads to some potentiallystriking conclusions. The functional outcomesof each system are, as for other reinforcer-controlled behaviours, likely to be susceptibleto the joint influences of the various interact-ing systems. Smillie et al. (2006) report theresults of simulation studies which illustratethis point. For one particular plausible set of interactions between the BIS, BAS andFFFS (in line with the revised Gray andMcNaughton, 2000, model) they simulatedfunctional outcomes (in this case meanoutput) across 200 randomly sampled andwidely varying combinations of reinforcers.The mean BAS output across simulated individuals was predicted (R2 = 0.89) by thefollowing regression equation:

Mean BAS output =(βA × wA) − (βF × wF) − (β I × w I)

where the βs are positive-valued regressioncoefficients. The same model showed thatmean BIS output was predicted (R2 = 0.85) by:

(β ¢A × wA) + (β ¢F × wF) + (β ¢I × w I)

By contrast, it is interesting to note that themean FFFS output was predicted (R2 = 0.82)only by the sensitivity of the FFFS.

Assuming some trait questionnaires doreflect functional outcomes of specific sys-tems then these simulations raise important and paradoxical results. For example, the‘BAS-related’ trait measures is BAS-relatedbecause it is defined by the functional outcome of the BAS and yet it is influencedby the sensitivities of all three interactingsystems (wA, wF and wI). Thus, if one were todevelop a new BAS trait measure then oneshould not consider it invalidated if it correlated negatively with anxiety (BIS trait)measures; the simulations predict that suchtrait correlations should be observed. These predictions occur, it is worth reiterating, eventhough wA and wI (the underlying systemsensitivities) are independent of one another.The description of the ‘reinforcement sensi-tivity’ theory of personality has implied aone-to-one mapping of traits (e.g. anxiety)onto the sensitivities of single systems (e.g.the BIS). The simulations show that this neednot be the case and trait measures may bejointly determined by the sensitivities of allthree interacting systems. It remains sensible,however, to talk of the theory as ‘reinforce-ment sensitivity’ theory, as the resulting personality traits are determined by the sensitivities of reinforcement-dependent systems; however, the one-to-one mapping of traits onto sensitivities is now being questioned.

In a speculative footnote to this section,we consider whether there might be sometrait measures which line up more directlywith underlying sensitivities rather thanfunctional outcomes? The simulations sug-gested that, for traits related to FFFS functioning, the two bases (sensitivities,functional outcomes) may sometimes bemore or less interchangeable. This fits wellwith the account proposed by McNaughtonand Corr (2004, 2008) in which the trait offearfulness (neurotic-introversion to stable-introversion) maps directly onto underlyingpunishment sensitivity.

However, one might also imagine a situa-tion in which a trait measure, T, had itemswhich reflected the functional outcome of one


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system along with other items which reflectedthe functional outcome of another system (wefinesse here the question of whether such atrait measure could ever emerge in a factoranalytic approach to trait measure develop-ment). Imagine such a measure was based ona mixture of BAS and BIS functional out-comes. The final trait measure (from theresults of the simulations presented earlier)would be given by a summation of the twoearlier regression equations:

T = (βA × wA) − (βF × wF) − (β I × wI) +(β ¢A × wA) + (β ¢F × w F) + (β ¢I × w I)

Assuming the values of β I and β′I, and βF

and β′F, were broadly similar then the aboveequation would approximately reduce to

T = (β A + β ¢A) × wA

In this scenario, the trait measure T woulddirectly reflect the sensitivity of a singleunderlying system (the BAS in this example).

High scores on such a trait measure wouldbe found in people who had higher BASfunctional outcomes (e.g. higher mean BASoutputs) and higher BIS functional outcomes(e.g. higher mean BIS outputs) across a rangeof situations. Is such a trait measure likely?Do any existing trait measures plausibly satisfysuch conditions? We do not think this islikely. It might be suggested that extraversionquestionnaires might be candidates for traitslike T above. The EPQ extraversion scale, forexample, has several items about enjoyingsocial situations (e.g. Do you enjoy meetingnew people? Would you enjoy yourself at alively party?); these can plausibly be viewedby indexing mean BAS output in these contexts. However, under Gray andMcNaughton’s (2000) reformulation of RST,and based on the description of the action ofthe BIS, someone with a high mean BISoutput would often be rather cautious anddeliberate, tending to seek extra informationwhen situations are ambiguous or whenmotivations are conflicting, and so on. Such

a person might be described as low impulsiveand deliberate. Items addressing these behav-ioural aspects might be found on some extra-version scales, and items addressing thesebehaviours on other scales would be verylikely to correlate moderately with traditionalextraversion items. However the correlationwould be the opposite way round to thatrequired for a trait measure such as T above;in our view, a trait measure like T thereforeseems very unlikely to exist.

In summary, the main message of this sec-tion remains: the role of underlying rein-forcement sensitivities in our revisedunderstanding of RST seems likely to bemore complex than has been hitherto sug-gested. With the possible exception of thepunishment / fear system, variations in thesensitivities of the underlying systems totheir characteristic inputs may not have one-to-one mappings onto observable per-sonality traits.

PERSONALITY ANDPSYCHOPATHOLOGY

How does personality relate to psychologicalconditions (e.g. anxiety). No doubt, the detailsof RST shall continue to undergo continualrefinement and change – that is in the nature ofany scientific theory – but we believe that‘defensive distance’ and ‘defensive direction’shall continue to play a pivotal role as theymap onto a series of distinct neural modules, toeach of which can be attributed a particularclass of function, and so generation of a partic-ular symptomatology (e.g. panic, phobia,obsession). As noted by McNaughton and Corr (2004, 2008), these ‘symptoms’ may begenerated in several different ways:

1 as a normally adaptive reaction to specific (mild)eliciting stimuli (e.g. mild anxiety just before anexam);

2 as excessive activation of a related structure byits specific (strong) eliciting stimuli, but wherethe ‘symptoms’ are not excessive given the level


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of input from the related structure (e.g. panicwhen crossing a railway line at the sight of a rapidly oncoming train);

3 at maladaptive intensity, as a result of excessivesensitivity to their specific eliciting stimuli (e.g. fearful avoidance as a result of seeing aharmless spider) – this would be a pathologicalreaction.

In addition, pathologically excessive (BIS)anxiety could generate (FFFS) panic with thelatter being entirely appropriate to the levelof apprehension experienced. Conversely,pathological panic could, with repeatedexperience, condition anxiety with the levelof the latter being appropriate to the panicexperienced. This modular view of thedefence system, separated into distinct syndrome and symptom-specific, componentswas developed largely on the basis of animalexperiments. In addition, the linking of thisview to terms such as panic, phobia, andobsession is also justified by the clinicaleffects of drugs when taken together as aclass. (All drugs have common and uniqueeffects, and it is only their common effectsthat interest us here.) RST may provide a sat-isfactory explanation of the variety of clinical‘neurotic’ phenomena observed, yet at thesame time, may appear to destroy the veryunity of an underlying personality trait.

However, this problem seems worse than itis. For rescue, we need only appeal to the factthat, based on quantitative genetic studies,there is a common fundamental predisposi-tion to the plethora of clinical neurotic condi-tions observed, even though thatpredisposition manifests differently in differ-ent individuals (Kendler et al., 2003). Indeed,the action of many clinically effective drugsis best viewed as an interaction with moreglobal modulatory systems. For example,5HT neurons innervate virtually the entiredefence system; and drugs such asimipramine or specific serotonin reuptakeinhibitors (SSRIs), have a general effect on5HT synapses. Such drugs affect anxiety,depression and panic because they increasethe levels of 5HT in the different parts of the system controlling each.

Therefore, comparison of drug classes canbe used to dissect out different parts of thedefence system. But this comparison mustinvolve several different drugs within eachclass if specific conclusions are to be drawnabout specific brain systems. Conversely, thesystems as a joint whole, and each systemindividually, may be globally susceptible tomodulation controlled by the biological substrates underlying personality. In detail,then, the system underlying clinical drug action consists of two sets of parallel, interconnected modules dealingwith defensive avoidance and defensiveapproach, respectively. Superimposed on these specialized modules are generalmodulatory systems.

It should be expected that if these modula-tory systems are crucial for personality, thereis also a conceptual need for general control.Certainly with the BIS, anxiolytics clearlyalter defensive distance: they alter at what-ever point of the neural hierarchy is in controlgiven progressive variations in the externalsituation, and they do so in a lawful manner.Assuming that the control of fear by themonoamines operates in a similar manner tothe control of anxiety by anxiolytic drugs, weshould expect the personality factor relateddirectly to ‘punishment sensitivity’ would bethe one that alters the internal defensive dis-tance in relation to any particular real dis-tance. Put another way, a personality factorof fearfulness multiplies the quantum of fearinherent in a particular stimulus, producingmany different levels (across different indi-viduals) with the same stimulus.

CONCLUSIONS

There remains some considerable uncer-tainty as the best way to relate fundamentalsystems of emotion and motivation to per-sonality factors, yet we contend that consid-erable progress has already been made. Thischapter has illustrated that there is a lot of new theorizing which has substantially


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reformulated a popular theory of personality.As yet, however, this new thinking has notstimulated many new empirical findings. Wehope that this situation will change in thenear future. In relation to this issue, Smillieet al. (2006: 320) note that although RST ismost often seen as a theory of anxiety andimpulsivity, it is ‘more accurately identifiedas a neuropsychology of emotion, motivationand learning. In fact, RST was born of basicanimal learning research, initially not at allconcerned with personality.’ They go on toremark, ‘RST did not develop as a theory ofspecific traits, but as a theory of specific bio-logical systems which were later suggestedto relate, inter alia, to personality’ (2006: 321).

There is a related reason why basic emo-tion and motivation systems do not mapneatly onto personality factors: basic emo-tion and motivation theory has extendedbeyond the point at which Gray suggestedthat the BIS and BAS relate to anxiety andimpulsivity, respectively. Furthermore, RSTpersonality researchers have developedscales to measure the BIS and BAS that wereinfluenced by Gray’s original thinking butwhich do not reflect more recent develop-ments in the basic theory. Thus, RSTresearch represents two distinct bodies ofknowledge, the first concerned with neuralsystems and processes, the second with personality and its measurement. One of our purposes in writing this chapter is toencourage other researchers to work to bring these two aspects into closer align-ment. Nonetheless, the Janus-faced nature of RST has also been a strength, making it a dynamically evolving theory, but it also poses obvious problems for, at any given time, specifying a consensual model agreed by researchers.

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