Dopaminergic and opioidergic regulation during anticipation and consumption of social and nonsocial rewards

Abstract

The observation of animal orofacial and behavioral reactions has played a fundamental role in research on reward but is seldom assessed in humans. Healthy volunteers (N = 131) received 400 mg of the dopaminergic antagonist amisulpride, 50 mg of the opioidergic antagonist naltrexone, or placebo. Subjective ratings, physical effort, and facial reactions to matched primary social (affective touch) and nonsocial (food) rewards were assessed. Both drugs resulted in lower physical effort and greater negative facial reactions during reward anticipation, especially of food rewards. Only opioidergic manipulation through naltrexone led to a reduction in positive facial reactions to liked rewards during reward consumption. Subjective ratings of wanting and liking were not modulated by either drug. Results suggest that facial reactions during anticipated and experienced pleasure rely on partly different neurochemical systems, and also that the neurochemical bases for food and touch rewards are not identical.

Facial EMG Activity Is Associated with Hedonic Experiences but Not Nutritional Values While Viewing Food Images

“…The liking ratings were negatively and positively associated with EMG activity of the corrugator supercilii [ 7 , 8 ] and zygomatic major muscles [ 7 ], respectively. Corroborating these data, other studies recorded EMG from these facial muscles while participants consumed liquid [ 9 , 10 , 11 ] or solid [ 12 ] food and showed similar associations between hedonic ratings, such as liking, wanting, and valence, and facial EMG activity of these muscles. Relatedly, some studies reported an association between facial expressions analyzed from video data and liking ratings during liquid food consumption [ 13 , 14 ].…”

“…Second, some previous studies using non-food visual stimuli have shown that facial EMG could detect unconscious emotional responses [ 57 , 58 , 59 ], which may also occur in the case of visual processing of food [ 60 , 61 , 62 , 63 ]. Third, a recent human pharmacological study showed that administration of opioid antagonists reduced zygomatic major EMG activity during the consumption of liked liquid food, but did not modulate the subjective ratings of liking and wanting [ 11 ]. The data suggest that facial EMG may more directly reflect activity in the brain reward circuits than subjective ratings under some conditions.…”

The Role of Mu-Opioids for Reward and Threat Processing in Humans: Bridging the Gap from Preclinical to Clinical Opioid Drug Studies

“…There is also consistent evidence that opioid blockade decreases reports of food enjoyment and reduces high caloric food consumption in humans [37,134,135,139]. A recent study also reported decreased effort to obtain food reward after MOR antagonism, but no effect on subjective ratings of food liking or wanting [64].…”

“…Petrovic et al [93] similarly reported larger effects of naloxone for high-value reward outcomes, which correlated with activity reductions in the rostral anterior cingulate. Administration of naltrexone also reduced motivation to exert effort for chocolate rewards in a pavlovian instrumental transfer task [130], attenuated motivational ratings following almost-wins in a gambling task [96], diminished learning in a reward-driven reinforcement learning task [34] and decreased physical effort to obtain a reward [64]. Some of these studies, including our own, tested only men due to what we now know is a misguided belief that female hormonal fluctuations would add more noise than those of males [106].…”

“…Korb et al [64] also reported opioid antagonist effects on facial muscle activity (more frowning during reward anticipation; less smiling during consumption of food rewards, in the absence of changes in subjective valuation of these rewards [64]). Increased negative facial reactions after opioid blockade were also reported during viewing of smiling faces [84], consistent with a role for MOR signalling in automatic behavioural responses (mimicry) that support social bonding [66].…”