Fig. 4.

Thin-spiking, type-2 neurons exhibit brief high-frequency bursts during singing. A: the raw voltage trace of a representative type-2 neuron and its instantaneous firing rate (see methods) are plotted beneath the song spectrogram (age 61 dph). B: interspike interval (ISI) distributions for the neuron shown in A during nonsinging (black), singing (blue), and interbout silent periods (red, see methods). C: spike train autocorrelation for the neuron from A exhibiting a narrow peak representing the brief bursts during singing. D: for each type-2 neuron, the mean firing rate during singing is plotted against the mean rate during interbout silence. E: the number of bursts per second during singing is plotted against burst incidence during interbout periods for each type-2 neuron. Triangles and circles, cells from subsong and plastic song birds, respectively. F, top: expanded view of a segment of the voltage waveform and spectrogram from B (indicated by red bar). Middle: spike raster showing activity of this neuron during 80 renditions of a 2-syllable motif. Bottom: rate histogram compiled from the raster plot. G: population histogram showing the distribution of significant rate peaks (blue) and rate minima (red) as a function of syllable timing (14 syllables from 6 type-2 neurons). Note that significant modulations occur throughout the syllables.