Intrinsic reward-like dopamine and acetylcholine dynamics in striatum

Abstract

External rewards like food and money are potent modifiers of behavior1,2. Pioneering studies established that these salient sensory stimuli briefly interrupt the tonic cell-autonomous discharge of neurons that produce the neuromodulators dopamine (DA) and acetylcholine (ACh): midbrain DA neurons (DANs) fire a burst of action potentials that broadly elevates DA levels in striatum3-5 at the same time as striatal cholinergic interneurons (CINs) produce a characteristic pause in firing6-8. These phasic responses are thought to create unique, temporally-limited conditions that motivate action and promote learning9-14. However, the dynamics of DA and ACh outside explicitly-rewarded situations remain poorly understood. Here we show that extracellular levels of DA and ACh fluctuate spontaneously in the striatum of mice and maintain the same temporal relationship as that evoked by reward. We show that this neuromodulatory coordination does not arise from direct interactions between DA and ACh within striatum. Periodic fluctuations in ACh are instead controlled by glutamatergic afferents, which act to locally synchronize spiking of striatal cholinergic interneurons. Together, our findings reveal that striatal neuromodulatory dynamics are autonomously organized by distributed extra-striatal afferents across behavioral contexts. The dominance of intrinsic reward-like rhythms in DA and ACh offers novel insights for explaining how reward-associated neural dynamics emerge and how the brain motivates action and promotes learning from within.