Ghrelin and risky decision-making: No credible evidence for homeostatic state modulation of neural or behavioural effects

Risk-taking is often thought to depend on homeostatic systems. However, evidence remains mixed, and the underlying mechanisms remain debated. One candidate that might drive changes in risky decision-making due to changes in homeostatic systems may be the hunger hormone ghrelin, which interacts with the dopaminergic system. In two studies, we examined the effects of experimental interventions known to affect ghrelin levels on human risky choice in healthy male participants, either after a brief fasting period (study 1, N = 37; N = 26 for fMRI analyses) or a single night of total sleep deprivation (study 2, N = 40; N = 36 for fMRI analyses). We found no credible effects of the experimental manipulations on the proportion of risky choices. In addition, computational modelling indicated that the standard prospect theory, without accounting for choice repetition, best described the observed behaviour. However, it did not reveal consistent effects of state manipulations on model parameters, and the inclusion of manipulation-induced changes in ghrelin levels in the model likewise revealed no robust associations. FMRI analyses did not reveal effects of state manipulation on neural signatures of subjective value or choice in a priori defined regions of interest (bilateral ventromedial prefrontal cortex, ventral striatum, posterior cingulate cortex, and anterior cingulate cortex for subjective value; bilateral anterior insula, ventral striatum, and right medial prefrontal cortex for choice). Our results suggest that state-dependent influences on risky decision-making may be weaker than previously thought.