Fig. 3.

Lesions of Area X alter firing patterns in LMAN without affecting firing rate increases during singing. (A) Song spectrograms (Upper) and singing-related activity of single LMAN neurons (Lower) in an intact (Left) and a lesion-deaf bird (Right). Note the increase in activity both before and during singing in both cases. (Inset) Fifty randomly selected spike waveforms sorted from single LMAN neurons are superimposed. (B) Raster plots of activity during 50 motif renditions (Upper) and when the bird was quiet (spontaneous activity, Bottom) for the neurons in A. (C) Smoothed instantaneous firing rates computed from the spikes of the same LMAN neurons (30 motifs overlaid). (D) Corresponding firing rate histograms for motif-aligned (solid line) and spontaneous activity (dotted line). (E) LMAN neurons in intact [n = 19 single units (circles) in nine birds] and lesion birds [n = 10 single units (circles) and 8 small clusters of units (triangles) in eight birds] increased their firing rates during singing. Red, data from lesion-deaf birds; purple, data from lesion-hearing birds. Statistical comparisons across experimental groups were performed on single units. (F) ISI histograms of LMAN neurons during singing in intact (black) and lesion-deaf birds (red) shown in A–D; shading highlights ISIs ≤ 5 ms (bursts). (G) Mean fraction of spikes that occurred as part of bursts (burst fraction). LMAN neurons exhibited burst firing in intact birds but not in lesion birds. Conventions as in E. **P < 0.0005.