Extraversion has two central characteristics: (1) interpersonalengagement, which consists of affiliation (enjoying and valuing close interpersonal bonds, being warm and affectionate) and agency (being socially dominant, enjoying leadership roles, being assertive, being exhibitionistic, and having a sense of potency in accomplishing goals) and (2) impulsivity, which emerges from the interaction of extraversion and a second, independent trait (constraint). Agency is a more general motivational disposition that includes dominance, ambition, mastery, efficacy, and achievement. Positive affect (a combination of positive feelings and (...) motivation) is closely associated with extraversion. Extraversion is accordingly based on positiveincentivemotivation. (shrink)

Because little is known about the human trait of affiliation, we provide a novel neurobehavioral model of affiliative bonding. Discussion is organized around processes of reward and memory formation that occur during approach and consummatory phases of affiliation. Appetitive and consummatory reward processes are mediated independently by the activity of the ventral tegmental area (VTA) dopamine (DA)–nucleus accumbens shell (NAS) pathway and the central corticolimbic projections of the u-opiate system of the medial basal arcuate nucleus, respectively, although these two projection (...) systems functionally interact across time. We next explicate the manner in which DA and glutamate interact in both the VTA and NAS to form incentive-encoded contextual memory ensembles that are predictive of reward derived from affiliative objects. Affiliative stimuli, in particular, are incorporated within contextual ensembles predictive of affiliative reward via: (a) the binding of affiliative stimuli in the rostral circuit of the medial extended amygdala and subsequent transmission to the NAS shell; (b) affiliative stimulus-induced opiate potentiation of DA processes in the VTA and NAS; and (c) permissive or facilitatory effects of gonadal steroids, oxytocin (in interaction with DA), and vasopressin on (i) sensory, perceptual, and attentional processing of affiliative stimuli and (ii) formation of social memories. Among these various processes, we propose that the capacity to experience affiliative reward via opiate functioning has a disproportionate weight in determining individual differences in affiliation. We delineate sources of these individual differences, and provide the first human data that support an association between opiate functioning and variation in trait affiliation. Key Words: affiliation corticolimbic-striatal networks; appetitive and consummatory reward; dopamine; oxytocin; personality; social bonds; social memory; u-opiates. (shrink)

Commentary on our target article centers around six main topics: (1) strategies in modeling the neurobehavioral foundation of human behavioral traits; (2) clarification of the construct of affiliation; (3) developmental aspects of affiliative bonding; (4) modeling disorders of affiliative reward; (5) serotonin and affiliative behavior; and (6) neural considerations. After an initial important research update in section R1, our Response is organized around these topics in the following six sections, R2 to R7.

The commentaries on our target article address three main areas: (1) the relative importance of extraversion and other related traits to DA functioning, (2) how the long-term stability of extraversion can be conceptualized within a highly plastic central nervous system, and (3) the nature of DA functioning in the MOC network and in extraversion. We have organized our Response, therefore, into three major sections.

Lifelines supports the theme that behavioral development is a fluid, life-long phenomenon. In contrast, many emotional and cognitive traits are subject to strong genetic influence, and are highly stable over many years. The manner in which neuroplasticity and trait stability cooccur needs to be modeled. An outline of such a model is provided to promote discussion of this complex issue.