Variable and slow-paced neural dynamics in HVC underlie plastic song production in juvenile zebra finches

Zebra finches undergo a gradual refinement of their vocalizations, transitioning from variable juvenile songs to the stereotyped song of adulthood. To investigate the neural mechanisms underlying song crystallization, a critical phase in this developmental process, we conducted intracellular recordings in HVC, a premotor nucleus essential for song learning and production. We found that HVC projection neurons in juvenile zebra finches in the song crystallization phase exhibited more variable spiking patterns compared to the precise bursting observed in adult HVC projection neurons. Additionally, subthreshold membrane potential fluctuations in juvenile neurons were characterized by longer duration and larger amplitude excitatory postsynaptic potentials. These distinct temporal dynamics in HVC during song crystallization likely play a crucial role in the fine-tuning processes that shape the precise timing and structure of the mature zebra finch song.