Jeffrey Markowitz - Dopamine specifies the statistics of spontaneous behavior
From Steven Marzec
Spontaneous animal behavior is built from action modules that are concatenated by the brain into sequences. However, the neural mechanisms that shape the composition of self-motivated behavior remain unknown. Here we show that dopamine systematically fluctuates in the dorsolateral striatum during spontaneous behavior as mice transition between sub-second behavioral modules, despite the absence of task structure, sensory cues or exogenous reward. Module-associated striatal dopamine levels predict future module use and ordering; closed-loop optogenetic manipulations demonstrate that dopamine increases sequence variation over seconds and reinforces associated behavioral modules over minutes, without directly influencing movement initiation or kinematics. Consistent with the possibility that the observed striatal dopamine fluctuations drive behavior, dopamine transients during spontaneous behavior are similar in magnitude to those observed during reward consumption, and mice choose modules on a moment-to-moment basis to maximize dopamine. Dopamine therefore acts as a continuous teaching signal that guides the composition of self-motivated behavioral sequences; these findings suggest a model in which the same circuits and computations that govern action choices in highly structured tasks play a key role in composing unconstrained, spontaneous behavior.