Modulation of social influence by methylphenidate

Abstract

The ability to infer value from the reactions of other people is a common and essential ability with a poorly understood neurobiology. Commonly, social learning matches one's values and behavior to what is perceived as normal for one's social group. This is known as conformity. Conformity of value correlates with neural activity shared by cognitions that depend on optimum catecholamine levels, but catecholamine involvement in conformity has not been tested empirically. Methylphenidate (MPH) is an indirect dopamine and noradrenalin agonist, commonly used for the treatment of attention-deficit hyperactivity disorder for which it reduces undesirable behavior as evaluated by peers and authority figures, indicative of increased conformity. We hypothesized that MPH might increase conformity of value. In all, 38 healthy adult females received either a single oral 20 mg dose of MPH or placebo (PL). Each subject rated 153 faces for trustworthiness followed immediately by the face's mean rating from a group of peers. After 30 min and a 2-back continuous-performance working-memory task, subjects were unexpectedly asked to rate all the faces again. Both the groups tended to change their ratings towards the social norm. The MPH group exhibited twice the conformity effect of the PL group following moderate social conflict, but this did not occur following large conflicts. This suggests that MPH might enhance signals that would otherwise be too weak to evoke conformity. MPH did not affect 2-back performance. We provide a new working hypothesis of a neurocognitive mechanism by which MPH reduces socially disruptive behavior. We also provide novel evidence of catecholamine mediation of social learning [corrected].

Figure 1

Conformity Task. Subjects rated 153 faces, one by one, for their expected trustworthiness on a scale from 1 to 8, indicated by pressing the corresponding number on a keyboard. The choice was highlighted by a green vertical rectangle. After rating each face, subjects learned the ‘social norm' rating of that face, which subjects were told was the average rating from four identical studies in European universities. The social norm rating was highlighted by a horizontal blue rectangle so that overlap with the subject's response could be observed. Social conflict with the norm could be ‘no conflict', moderate (±2), or high (±3). Subjects were told that low conflict (±1) would be displayed as ‘no conflict'. Unexpectedly, subjects rated the faces again after 30 min, in a random order, without social feedback. Display was presented to subjects in color.

Figure 2

Methylphenidate Effect on Conformity. Subjects treated with methylphenidate conformed more following moderate social conflict. (a) Change of value (C_opin) for moderate social conflict magnitudes of −2, NC, and 2. Error bars reflect one within-subject SE. (b) Change of value towards social norm (C_twrd) for moderate (±2) and high (±3) social conflict conditions. Error bars reflect one between-subject SE.