Extraversion and Reward Processing

Paradigm Shift: Reward Processing

Over the past few decades, explanatory mechanisms relating to the processing of reward stimuli have become salient features of personality theory. Their origins can be traced to the work of Jeffrey Gray (1973), who proposed that differences in the sensitivity of the neural system involved in processing reward might form a partial basis for personality variation. Gray and his colleagues were somewhat tentative in identifying which personality traits might emerge from variations in reward-system functioning, but Richard Depue’s work in the 1990s offered an explicit reward-processing view of extraversion (e.g., Depue & Collins, 1999). At the heart of both Gray’s and Depue’s theories are structures and functions of the midbrain dopamine system, which are involved in the regulation of incentive motivation and behavioral approach of reward. This perspective has been retained throughout the rise of personality neuroscience, such that the views of those at the forefront of the field tend to clearly reflect Gray’s and Depue’s influences (e.g., Canli, 2004; DeYoung, 2010).

The growing number of published references to reward-processing theories of extraversion over the past three decades is illustrated in Figure 1. For comparative purposes, Figure 1 also presents the number of references to Hans Eysenck’s (1967) arousal theory; an earlier, biological model of extraversion that dominated the field for many years. Despite the long shadow cast by Eysenck’s theory, its influence has fallen behind that of the reward-processing view, such that the latter is more visible today than was the former in its prime.

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Fig. 1.

The shift toward a reward-processing view of extraversion. Publications whose abstracts refer to extraversion and to reward, behavioral activation system (BAS), or dopamine (key terms in Gray’s and Depue’s theories) are represented by the solid green line. Publications whose abstracts contain the terms extraversion and arousal, ascending reticular activating system (ARAS), or reticular (key terms in Eysenck’s theory) are represented by the dashed red line. Data in this graph were drawn from a search of the PsycINFO (www.apa.org/psycinfo) and PsycArticles (www.apa.org/psycarticles) databases by the author in September 2012.

An appealing feature of the reward-processing view is its potential to account for the coherence of the basic psychological components comprising trait extraversion. That is, variation in reward responsivity may explain why people who tend to be sociable tend also to be outgoing and to experience high levels of positive affect. There is no a priori reason to expect these patterns of affect and behavior to “go together” in terms of their joint covariation across individuals. However, outgoing behaviors (e.g., playing sports, partying) and social behaviors (e.g., dating, spending time with friends) all typically involve approaching rewards. Furthermore, greater engagement with rewarding stimuli and situations is likely to result in more frequent or more intense experiences of positive affect. Plausibility of the reward-processing view is further bolstered by the fact that sociable and outgoing behaviors that do not involve approaching reward are less central to extraversion. For instance, altruistic behaviors and feelings of empathy—which are typically linked with trait agreeableness rather than extraversion—are quintessentially social but are not obviously connected with reward pursuit.

The accumulated empirical support for the reward-processing view of extraversion is notable for the variety of methods on which it draws. Extraversion has been associated with (a) genetic variations linked with dopamine function and reward-seeking behavior; (b) differential hormonal and behavioral responses to dopaminergic drugs; (c) volumetric measures of brain structures involved in the processing of rewards; (d) neural responses to reward events, recorded using brain-imaging techniques such as functional MRI (fMRI); and (e) behavioral pursuit of reward and reward-based learning (see DeYoung, 2010, and Smillie, 2008, for reviews of this seminal work). It is important to note that this empirical support may be more compelling in its breadth than in its depth: Although one can easily locate a wide range of findings linking extraversion with reward-reactivity, clear replications of any one such finding are considerably more rare (as noted by Hutcherson, Goldin, Ramel, McRae, & Gross, 2008, pp. 71–72).

Among other recent contributions to this literature, my colleagues and I have shown that extraversion is associated with an electrophysiological signature of dopaminergic processing of reward (e.g., Smillie, Cooper, & Pickering, 2011). We had participants engage in a simple gambling task that was similar to a casino slot-machine. The majority of trials consisted of the presentation of either two gold-bar images in a row, with the second accompanied by a monetary reward (predicted-reward trial), or two lemon images in a row, with the second accompanied by no reward (predicted-nonreward trial). In contrast with these, a minority of trials consisted of either the presentation of a gold bar followed by a lemon and its associated nonreward (unpredicted- nonreward trial) or the presentation of a lemon followed by a gold bar and its associated reward (unpredicted-reward trial).

The impact of the unpredicted trials can be detected using a measure of brain activity known as frontal-related negativity. This measure potentially reflects the role of dopamine in signaling that either an unexpected reward has occurred or an expected reward has not occurred—a so-called reward-prediction error (Schultz, 1997). Of greatest relevance to the reward-reactivity view of extraverison was our finding that the difference in frontal-related negativity between these two trial types—an index that we suggest may relate to the overall magnitude of reward-prediction error—was larger for extraverts than for introverts. My colleagues and I have recently replicated this finding and demonstrated that it generalizes beyond trait extraversion to other personality measures concerned with reward anticipation (Cooper, Duke, Smillie, & Pickering, 2013).

Desire for Versus Enjoyment of Reward

Reward processing is often flexibly interpreted in terms of such phenomena as affective reactions to received rewards, behavioral efforts expended to obtain rewards, and neural activity during reward evaluation. However, a number of literatures have converged on the idea that there exist qualitatively distinct aspects of reward processing that should not be treated interchangeably. Animal models of addictive behavior have yielded a distinction between wanting, or the motivational desire for rewards supported by the functions of the midbrain dopamine system, and liking, or the pleasurable impact of rewards based in the forebrain opioid system (Berridge, Robinson, & Aldridge, 2009). A similar dichotomy has emerged in relation to temporal aspects of reward-processing, such that prereward processing has been attributed to midbrain functions and postreward processing attributed to forebrain functions (Knutson & Bhanji, 2006). Also relevant is the distinction between positive affective states that are low in approach-motivation intensity (e.g., feelings of contentment) and those that are high in approach-motivation intensity (e.g., feelings of excitement; Harmon-Jones, Price, & Gable, 2012). Together, these literatures suggest that processes involved in the motivational orientation toward to-be-obtained rewards (or reward desire) are separate from those involved in the valenced emotions experienced upon the attainment or consumption of rewards (or reward enjoyment).

It is perhaps an underappreciated fact that reward desire and reward enjoyment have been distinguished in the context of extraversion. Specifically, Depue and Collins (1999) identified two distinct constructs subsumed within broad measures of extraversion. One of these, agency, concerns achievement-related behavior and social dominance; the other, affiliation, concerns pleasant feelings and enjoyment of social closeness. Similar distinct subcomponents of extraversion have been identified elsewhere in the literature (e.g., assertiveness vs. enthusiasm; DeYoung, 2010), as well as in content analyses of questionnaire measures of extraversion (see Wilt & Revelle, 2009). However, it is important to note that Depue’s concept of affiliation appears at least partly relevant to trait agreeableness. Depue and Collins (1999) argued that agentic extraversion was related to the reward-approach-motivating functions of the midbrain dopamine system. Conversely, affiliative extraversion was thought to relate to the pleasure-generating functions of the forebrain opioid system (Depue & Morrone-Strupinsky, 2005). In addition, agentic extraversion was linked to prereward appetitive processes, whereas affiliative extraversion was linked to postreward consummatory processes. In sum, processes concerning reward desire and reward enjoyment have been conceptually, temporally, and biologically distinguished in reward- processing accounts of extraverted personality.

Despite this strong theoretical precedent, separable aspects of reward processing are only faintly reflected by empirical trends in the extraversion literature. Some studies have shown that agentic extraversion differentiates responses to dopaminergic drugs (e.g., Wacker, Chavanon, & Stemmler, 2006), whereas affiliative extraversion differentiates responses to opioid-acting drugs (e.g., Depue & Morrone-Strupinsky, 2005). Most studies, however, have not distinguished between reward desire and reward enjoyment.

My colleagues and I recently showed that this broad brushstroke approach to reward processing may generate confusion (Smillie, Cooper, Wilt, & Revelle, 2012). This work related to the hypothesis that dispositional reward-reactivity, arising from the functions of Gray’s and Depue’s dopaminergic reward system, should lead extraverts to be particularly susceptible to the experience of pleasant mood (see Lucas & Baird, 2004). We suggested that this prediction conflates the motivational desire for rewards with the experience of rewards as enjoyable—which might explain the considerably mixed support it has yielded. Five experiments and a small meta-analytic review confirmed our suspicions. Specifically, we found that extraversion did not confer a general susceptibility to the induction of pleasant feelings (e.g., contentment). Rather, when mood was induced in a manner consistent with the concept of reward desire or approach (e.g., winning money or watching a video depicting goal pursuit), extraverts were susceptible to increases in approach-motivated positive affect (e.g., feelings of vigor and excitement). Figure 2 depicts a representative finding from these studies, in which extraversion is associated with higher approach-motivated positive affect only after a positive-mood induction involving highly salient elements of reward approach.

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Fig. 2.

Relation between trait extraversion and approach-motivated positive affect following a positive-mood induction that is either low or high in approach-motivation intensity (from Smillie, Cooper, Wilt, & Revelle, 2012). Low extraversion was defined as extraversion scores more than 1 SD below the mean trait score, and high extraversion was defined as scores more than 1 SD above the mean trait score.

In light of Depue and colleagues’ theorizing, one might expect that susceptibility to approach-motivated positive affect should relate specifically to agentic extraversion. Conversely, affiliative extraversion, which is characterized by feelings of pleasantness and warmth, might confer a greater susceptibility to pleasant affective states that are lower in approach-motivation intensity. My colleagues and I recently tested this prediction and found that markers of agentic and affiliative extraversion both predict increased approach-motivated positive affect following an appetitive-mood induction (Smillie, Geaney, Wilt, Cooper, & Revelle, in press). Consistent with our previous findings, results showed that neither aspect of extraversion predicted increased pleasant affect following a mood-induction procedure characterized by low reward approach (e.g., imagining relaxing on the beach). However, affiliative extraversion was strongly and uniquely related to measures concerning global pleasant affect (e.g., happiness and satisfaction with life). Our findings imply that extraversion may relate to momentary increases in reward desire, but also to more chronically elevated feelings of pleasure and satisfaction, which may be a long-term consequence of reward enjoyment. Further research is needed to evaluate this possibility. More generally, future research into extraversion and reward processing should heed the conceptual, temporal, and biological dissociations that have been drawn between reward desire and reward enjoyment.

Higher-Level Conceptions of Reward Processing

Although the reward-processing view of extraversion has its roots in the biologically oriented perspectives of Gray and Depue, reward mechanisms can also be identified in a range of theories situated at higher levels of analysis. For example, Robinson (2007) has suggested that extraversion may be related to cognitive biases concerning the integration of positive information in memory networks. This hypothesis derives from affective-priming studies, which have shown that extraverts identify positive information more quickly than introverts do after exposure to an initial positive stimulus. Reward-related mechanisms are also evident in social-process theories of extraversion. For instance, Ashton, Lee, and Paunonen (2002) have suggested that extraversion emerges from a repertoire of behavioral strategies—such as friendliness and dominance—that collectively function to attract social attention and that are sustained by the experience of social attention as rewarding. Somewhat similarly, Eaton and Funder (2003) have shown that extraverted behavior contributes to the positivity of social environments, which are consequently made more enjoyable and rewarding for the extraverted individual.

One body of literature that is perhaps easily overlooked in this context concerns the study of autobiographical narratives—the internalized stories that we construct to give our lives a sense of unity and purpose. Dan McAdams and others have shown that pivotal episodes in autobiographical narratives are often characterized by themes of agency (e.g., autonomy, achievement, status) and communion (e.g., friendship, community, dialogue; e.g., McAdams, Hoffman, Mansfield, & Day, 1996). These themes have a striking resemblance to the concepts of agency and affiliation in Depue’s reward- processing theory of extraversion. In two studies of the associations between personality traits and autobiographical narratives, extraversion was strongly associated with communion themes (McAdams et al., 2004). Extraversion was also associated with agentic themes, such as social status, although these associations were weaker and less consistent across studies (possibly owing to the broad focus of the authors’ measure of extraversion). Interestingly, these findings were not anticipated, and the potential theoretical relevance of communion and agentic themes to extraverted personality does not appear to have been highlighted in the literature to date.

These higher-level approaches to the study of extraversion and reward-processing may complement the personality-neuroscience route. Although it seems unlikely that all of these perspectives reflect a common explanatory mechanism, they nevertheless represent striking thematic convergence in personality science.

Conclusion

Reward-processing perspectives have increasingly shaped our understanding of extraverted personality. The growing field of personality neuroscience has expanded our knowledge of the role that neural processing of reward may play in extraversion. However, relatively little of this work has distinguished between desire for and enjoyment of rewards, and few connections have been made between this literature and potentially compatible literatures targeting higher levels of analysis. Future investigations should take advantage of these promising avenues of research.

Recommended Reading

Depue, R. A. (2006). Interpersonal behavior and the structure of personality: Neurobehavioral foundation of agentic extraversion and affiliation. In T. Canli (Ed.), Biology of personality and individual differences (pp. 60–92). New York, NY: Guilford Press. A comprehensive overview of Depue’s reward-processing theory of extraversion.

Smillie, L. D., Cooper, A., Wilt, J., & Revelle., W. (2012). (See References). A series of recent experiments examining extraverts’ susceptibility to approach-motivated positive affect.

Wilt, J., & Revelle, W. (2009). (See References). A review of the literature on extraversion with a much broader theoretical perspective than the present article.