a, Three neurons recorded from Bird 2 during protosyllable stage (top: HVCX; 63 dph; bottom: simultaneous recording two neurons; both HVCX; 64 dph; scale bar 0.5 mV). b, Raster plot of 28 HVC projection neurons aligned to protosyllable onsets (sorted by latency; 57–64 dph, Bird 2). Antidromically identified HVCRA neurons indicated by circles at right. c, Distribution of burst latencies relative to syllable onset in subsong stage (top), protosyllable stage (middle), and multi-syllable/motif stages (bottom), across all birds (n=19, 104, 814 neurons, respectively). Black triangle: median burst times.