Opioid receptor blockade and warmth-liking: effects on interpersonal trust and frontal asymmetry

Abstract

The emotion 'warmth-liking' (WL) associated with feelings of affection and acceptance is regularly activated in social contexts. WL has been suggested to be more closely related to the consummatory phase of post-goal attainment positive affect than to pre-goal attainment positive affect/approach motivation and to be partly mediated by brain opioids. To validate these assumptions we employed film/imagery to induce either a neutral emotional state or WL in female participants after intake of either placebo or the opioid antagonist naltrexone. Dependent variables were emotion self-report, interpersonal trust (TRUST, i.e. a behavioral indicator of WL) and frontal asymmetry (i.e. an electroencephalogram (EEG) indicator of approach motivation/behavioral activation). We found that participants reported more WL in the placebo/WL group than in the placebo/neutral group and both naltrexone groups. In addition, TRUST increased in the WL group after placebo, but not after naltrexone, and this pattern was reversed in the neutral control groups. Consequently, opioid blockade suppressed or even reversed the effects of the WL induction on the levels of self-report and behavior, respectively. In addition, we observed reduced relative left-frontal asymmetry in the WL (vs neutral) group, consistent with reduced approach motivation. Overall, these results suggest opioidergic influences on WL and TRUST and reduced approach motivation/behavioral activation for the positive emotion WL.

Keywords: endogenous opioids; frontal asymmetry; interpersonal trust; positive emotion; psychopharmacology.

Fig. 1

The trust game. Both players receive a starting capital of 10€. The investor then decides how much of this money he wants to give to the trustee presented in a photograph. The trustee receives the investment after triplication by the experimenter and is given the choice to return any amount between 0 and the total sum of money available to him (investment*3 + 10€). The back transfer is not tripled again. As an example, the investor decides to invest 5€, the trustee’s total amount is 25€, because of the triplication and his own starting capital. The trustee can now return any amount between 0 and 25€. Therefore, the investor’s profit depends on his investment and the trustee’s back transfer. The next trail starts with a new trustee and a new starting capital of 10€. Participants completed 10 trials as investor in each of the two trust games.

Fig. 2

Schematic of the procedure during the main testing session. The initial rest period started about 60 min after intake of the pill and was followed by repeated administrations of an emotional self-report and the trust game, before and after an emotion induction through personal memories and brief film clips. Subsequently, participants completed a real-estate game and rated the trustworthiness of the trustees encountered in the trust game.

Fig. 3

Mean WL ratings (left) and WE ratings (right) in the four experimental groups over time. CO, neutral control; Pre, before emotion induction; Post 1, after emotion induction; Post 2, after second trust game.

Fig. 4

Mean interpersonal trust in the four experimental groups over time.

Fig. 5

Frontal low alpha asymmetry in the four experimental groups for initial rest period, personal memories and film imagery EEG recordings.