Quantification of song-evoked spiking patterns in RA projection neurons with 5-HT application. Neurons fired more in general, and also fired more song-related spikes during bursts, n = 5 neurons in 4 animals. A, RA neurons were selective for BOS over reverse BOS, conspecific song, or white noise. B, Application of 5-HT significantly increased the number of spikes per burst evoked by BOS. C, 5-HT also significantly increased the duration of bursts evoked by BOS. D, Response strength decreased with application of 5-HT, primarily due to the increase in spontaneous firing rate that 5-HT causes.