Cortico-Striatal Beta-Oscillations as a Marker of Learned Reward Value

Single neuron correlates of reward value have been observed in brain regions along the cortico-striatal pathway including ventral striatum, orbital, and medial prefrontal cortex. Brain imaging studies in humans further validate these findings and suggest that value is represented in a reward network opposed to a particular brain region. To explore how a learned reward value signal may be communicated across a widespread, dynamic network, we measured local field potentials of male Long-Evans rats performing three distinct behavioral tasks, each probing a different aspect of reward-processing. Our goal was to identify a common electrophysiology property linked with reward value. We found that oscillations at beta frequencies that occurred during the reward outcome period served as a robust marker of learned reward value. Beta-oscillations signaled positive reward valence and scaled in predictable ways with subjective reward value modulated by temporal discounting and reversal learning. Oscillatory signatures of reward-processing were observed across canonical reward-regions including orbitofrontal cortex, anterior insula, medial prefrontal cortex, ventral striatum, and amygdala. Activity of single-units in orbitofrontal cortex were also selectively modulated at beta frequencies during positive valence reward outcome. This data suggests that beta-oscillations reflect learned reward value in a distributed network that may serve as a stable and robust bio-marker for future studies. Significance Statement Using large-scale measurements of local field potentials, we found that activity within a cortico-striatal circuit, operating at beta/gamma frequencies, was associated with reward valence, and scaled with temporal discounting and reversal learning.