A randomized controlled experimental medicine study of ghrelin in value-based decision making

BACKGROUND. The stomach-derived hormone ghrelin stimulates appetite, but the ghrelin receptor is also expressed in brain circuits involved in motivation and reward. We examined ghrelin effects on decision making beyond food or drug reward using monetary rewards. METHODS. Thirty participants (50% women and 50% men) underwent 2 fMRI scans while receiving i.v. ghrelin or saline in a randomized counterbalanced order. RESULTS. Striatal representations of reward anticipation were unaffected by ghrelin, while activity during anticipation of losses was attenuated. Temporal discounting rates of monetary reward were lower overall in the ghrelin condition, an effect driven by women. Discounting rates were inversely correlated with neural activity in a large cluster within the left parietal lobule that included the angular gyrus. Activity in an overlapping cluster was related to behavioral choices and was suppressed by ghrelin. CONCLUSION. This is, to our knowledge, the first human study to extend the understanding of ghrelin's significance beyond the canonical feeding domain or in relation to addictive substances. Contrary to our hypothesis, we found that ghrelin did not affect sensitivity to monetary reward anticipation, but rather resulted in attenuated loss aversion and lower discounting rates for these rewards. Ghrelin may cause a motivational shift toward caloric reward rather than globally promoting the value of reward. TRIAL REGISTRATION. EudraCT 2018-004829-82.