Temporal dynamics of noradrenaline release at fine spatial scales during motor learning

Noradrenaline (NA) released from the locus coeruleus (LC) has been known to play pivotal roles in arousal, sensory processing, decision-making, and learning through global release across the entire neocortex. Recent studies have demonstrated heterogeneous and modular NA release in distinct brain regions and highlighted its spatiotemporal dynamics across the neocortex. However, the spatiotemporal specificity of NA release at fine scales within a single brain region remains unclear, and it has not been reported whether the release patterns evolve functionally throughout prolonged learning processes such as motor skill acquisition. Here, by employing in vivo two-photon imaging with various genetically encoded NA sensors, we reveal that behavior-induced NA release in the primary motor cortex (M1) is spatially heterogeneous at the scale of local microcircuitry. Over the course of learning, the release pattern is locally refined, achieving consistent spatial precision within M1. Intriguingly, pharmacological manipulations that disrupt the spatial specificity also alter local neurons activity and representations. Furthermore, LC-NA axonal calcium imaging uncovered two distinct temporal activity patterns, in which non-behavior-related rapid axonal activity (sub-second duration events) profoundly affect the temporally precise behavior-induced persistent axonal activity (seconds duration events). Closed-loop optogenetic manipulations that bi-directionally modulate non-behavior-related rapid events directly impacted the learning process. Together, our results provide novel insights into the temporal dynamics of NA release at fine spatial scales within one brain region and underscore the critical role of local NA specificity in regulating circuit plasticity during motor skill acquisition.