A synaptic locus of song learning.

Learning by imitation is the foundation for verbal and musical expression, but its underlying neural basis remains obscure. A juvenile male zebra finch imitates the multisyllabic song of an adult tutor in a process that depends on a song-specialized cortico-basal ganglia circuit, affording a powerful system to identify the synaptic substrates of imitative motor learning. Plasticity at a particular set of cortico-basal ganglia synapses is hypothesized to drive rapid learning-related changes in song before these changes are subsequently consolidated in downstream circuits. Nevertheless, this hypothesis is untested and the synaptic locus where learning initially occurs is unknown. By combining a computational framework to quantify song learning with synapse-specific optogenetic and chemogenetic manipulations within and directly downstream of the cortico-basal ganglia circuit, we identified the specific cortico-basal ganglia synapses that drive the acquisition and expression of rapid vocal changes during juvenile song learning and characterized the hours-long timescale over which these changes consolidate. Furthermore, transiently augmenting postsynaptic activity in the basal ganglia briefly accelerates learning rates and persistently alters song, demonstrating a direct link between basal ganglia activity and rapid learning. These results localize the specific cortico-basal ganglia synapses that enable a juvenile songbird to learn to sing and reveal the circuit logic and behavioral timescales of this imitative learning paradigm.