Figure 4.

Singing-related HVC_X burst spikes in alternative transition segments. A, B, The effects of the upstream trajectories on the firing rate in the alternative transition segments were examined. Each row represents upstream transitions toward a given junction or branching syllable, where the bursts were observed. The same statistical analysis shown in Figure 3C was performed. A, The statistical results for the HVC_X bursts associated with junction transition segments with or without branching transitions. B, The results for the HVC_X bursts associated with branching transition segments without junction transitions. The lowest p value among alternatives was plotted using a color code (red, p < 0.05; blue, p ≥ 0.05). Black indicates linear transition segment and insufficient sampling (fewer than four samples). C, The syllable-selective bursts whose firing rates were constant among alternatives (s1–s15 in A and B) preserved the relative onset timings to the associated syllables independently of the adjacent syllable types. Primary or nonprimary transitions were defined by the order in the song sequences. Error bars represent ±SD. D, The changes in spike rate of the all-or-none type transition-selective activity between primary and nonprimary transitions (a1–a20 in A). Primary or nonprimary transitions were determined by the average spike rate. Error bars represent ±SD. E, Neuronal reliability (probability of activity per transition segment) of the intermediate type transition-selective activity (i1–i8 in A and B). Red and blue represent reliability in a primary transition and in a secondary transition, respectively. Primary or secondary transitions were determined by the average firing rate. F, Example of intermediate type transition-selective activity (i8 in B and E) recorded from the bird that generated song sequences according to the syntax illustrated in Figure 1A.