The interoceptive origin of reinforcement learning

Rewards play a crucial role in sculpting all motivated behavior. Traditionally, research on reinforcement learning has centered on how rewards guide learning and decision-making. Here, we examine the origins of rewards themselves. Specifically, we discuss that the critical signal sustaining reinforcement for food is generated internally and subliminally during the process of digestion. As such, a shift in our understanding of primary rewards as an immediate sensory gratification to a state-dependent evaluation of an action's impact on vital physiological processes is called for. We integrate this perspective into a revised reinforcement learning framework that recognizes the subliminal nature of biological rewards and their dependency on internal states and goals.