The maintenance of homeostasis is essential to all the biological systems in the body. Caloric deprivation (relative to satiety) may lead to changes in reward and motivation signaling in the CNS that are not limited to appetite. The current work isolated metabolic state changes in reward anticipation signaling using a modified Monetary Incentive Delay task (MID), in conjunction with functional Magnetic Neuroimaging (fMRI). The MID task included both immediate and delayed (1 month) monetary rewards.
Healthy normal-weighted participants (n = 18) participated in two imaging sessions. Participants came to each session after at least 12 hours of fasting, and in only one of the sessions were given a complete meal prior to neuroimaging (order randomized). We carried out both whole-brain and region-of-interest (ROI) analyses directed at identifying changes in reward anticipation signaling as a function of reward immediacy, reward magnitude, and of metabolic state.
Not surprisingly, signal increases were greater during anticipation of immediate reward than (relative to delayed reward) within task-active voxels in the caudate, insula, putamen, thalamus, nucleus accumbens, and supplementary motor area (no significant effect of reward magnitude was observed). More importantly, ROI analyses revealed that the caloric deprivation was associated with increased reward signaling within this same network (most prominently within the putamen, insula, thalamus and supplementary motor area). This metabolic-state differential was consistent across all monetary reward conditions.
Results of this study confirms metabolic state changes in reward anticipation signaling are not limited to appetite. Ongoing work in our lab will examine whether changes in reward anticipation signaling impact decision making.