Acetylcholine-dependent phasic dopamine activity signals exploratory locomotion and choices
Dopamine neurons from the Ventral Tegmental Area (VTA) switch from tonic to phasic burst firing in response to reward-predictive cues and actions. Bursting is influenced by nicotinic acetylcholine receptors (nAChRs), which are not implicated in reinforcement learning, but rather in exploration and uncertainty-seeking. The leading model assigns these functions to tonic dopamine firing. To investigate this paradox, we recorded the activity of VTA dopamine neurons during a spatial decision-making task. When reward was certain, mice adopted a stereotyped behavior, and dopamine neurons signaled reward. When confronted with uncertain rewards or a novel environment, mice exhibited exploration. Modulation of phasic, but not tonic, dopamine activity predicted uncertainty-seeking and locomotor exploration. Deletion of nAChRs disrupted the influence of uncertainty and novelty on dopamine firing and behavior, sparing reward signaling and learning. Hence, nAChR modulation of dopamine neurons can influence cognitive functions on a short timescale, through the modulation of phasic, synchronous bursting.