Ghrelin is related to lower brain reward activation during touch

Abstract

The 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 slow caressing touch (so‐called CT‐targeted 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. CT‐targeted touch was rated as the most pleasant and activated somatosensory and reward networks (whole brain). A region‐of‐interest in the right medial orbitofrontal cortex (mOFC) showed lower activation during all touches, the higher the ghrelin concentrations were. During CT‐targeted touch, a larger satiety response (ghrelin decrease after the meal) was associated with higher mOFC activation, and this mOFC activation was associated with higher experienced pleasantness. Overall, higher ghrelin concentrations appear to be related to a lower reward value for touch. Ghrelin may reduce the value of social stimuli, such as touch, to promote food search and intake in a state of low energy. This suggests that the role of ghrelin goes beyond assigning value to food reward.

Affective Touch is encoded by pupil dilation as a comprehensive social phenomenon

“…In our study, we also invited participants to rate the pleasantness of the touch they received. Consistent with prior research (Ali et al, 2023;Pfabigan et al, 2023;van Hooijdonk et al, 2019;von Mohr et al, 2017;Zheng et al, 2021), our participants reported higher levels of pleasantness when the touch was administered at the CT-optimal speed and when delivered by a human rather than an artificial hand. Crucially, self-reports mirrored pupil results by revealing that participants reported the highest ratings of pleasantness when tactile stimulation featured both CT-optimal speed and human contact simultaneously.…”

Ghrelin decreases sensitivity to negative feedback and increases prediction-error related caudate activity in humans, a randomized controlled trial

“…From an evolutionary perspective, it could be hypothesized that ghrelin would not simply increase sensitivity to all rewards and decrease sensitivity to all negative outcomes. This is supported by the recent report of decreased hedonic responses to affective touch during higher amounts of ghrelin [ 59 ]. However, monetary rewards are domain-general, as they can be used to gain any type of reward, not just food.…”

Chronic Social Defeat Stress Increases Brain Permeability to Ghrelin in Male Mice

“…Within the VMH, the increase in fluorescent ghrelin binding and c- fos expression were primarily observed in the ventrolateral portion, a subregion in the VMH that is linked to social behaviors that include mating and aggression in mice, and not with metabolic function ( Lin et al, 2011 ; Falkner et al, 2016 ; Flanigan and Russo, 2019 ). Ghrelin has been linked to behavioral responses with a social component, and some have suggested that ghrelin may play a role in maintaining social behaviors ( Park et al, 2021 ; Pfabigan et al, 2024 ), and resilience in general, in the face of significant stressors like the stress experienced by socially defeated mice ( Lutter et al, 2008 ).…”