Coding of reward uncertainty and probability by orexin neurons

Abstract

Activation of hypothalamic hypocretin/orexin neurons (HONs) is a neural substrate of arousal. HONs activate during sensory stimuli, and are thus thought to regulate arousal according to sensory input. Here, we measured body movements occurring during sound cues or associated reward outcomes, and used an encoding model to ask whether HONs indeed specialize in tracking certain features, or multiplex diverse types of features. Although some single HONs multiplexed feature combinations, during the cue period the overall HON signal primarily tracked body movements. This persisted across cues signaling different reward probabilities, and substantially diverged from reward-probability tracking in concurrently-recorded VTA dopamine neurons. In contrast, during reward outcome, HONs predominantly signaled the presence or absence of reward, and not body movements, nor surprise or reward prediction error. These results describe an unexpectedly specialized and flexible logic of HON activation, suggesting a role for HONs in tracking actions and subsequent reinforcements.