The “hunger” hormone ghrelin is associated with neural activation during touch, but not its affective experience

Abstract

AbstractThe gut hormone ghrelin drives food motivation and increases food intake, but it is also involved in the anticipation of and response to rewards other than food. This pre-registered study investigated how naturally varying ghrelin concentrations affect the processing of touch as a social reward in humans.Sixty-seven volunteers received “social-affective” touch as a social reward and control touch on their shins during 3T functional imaging on two test days. On one occasion participants were fasted and on another they received a meal. On each occasion plasma ghrelin was measured at three time points.All touch was rated as more pleasant after the meal, but there was no association between ghrelin concentrations and pleasantness. Social-affective touch was rated as most pleasant and activated somatosensory and reward networks (whole-brain). A region-of-interest in the right medial orbitofrontal cortex (mOFC) showed decreased activation during all touch when ghrelin concentrations were high. During social-affective touch, a larger satiety response (ghrelin decrease after the meal) was associated with higher mOFC activation, and this OFC activation was associated with higher experienced pleasantness.Overall, high ghrelin concentrations appear to be related to decreased reward value. Ghrelin may carry a negative valence signal that, however, does not alter subjective experience. Ghrelin’s observed involvement in the processing of social-affective touch speaks to its multifaceted role in reward processes beyond motivating food search and consumption.