Developmental changes in mouse motor skill learning and cortical circuitry.

Plasticity in sensory cortex is restricted to a limited developmental window. Learning motor skills requires motor cortex plasticity, but it is unknown whether there are changes in learning aptitude over development and whether the synaptic mechanisms of plasticity vary across cortical areas. Here, we define the developmental trajectory of motor learning aptitude for the accelerating rotarod task in mice. We find that learning peaks at P30-P45, with mice learning to shift from hopping to walking gait to stay on the rotarod longer. Further, the gait shift in forelimbs precedes hindlimbs. We then find, using recordings targeted to task-active neurons, that inhibitory responses from specific subtypes of interneurons (parvalbumin-expressing) are stronger in active cells, while other interneuron connections (somatostatin-expressing) are unchanged. These results suggest early changes in PV-mediated inhibition support motor skill acquisition.