Effects of coherence and phase alignment on vocal γ. A, Time-frequency plot of phase coherence between LFP responses and vocal acoustic frequency contours for a sample recording. Coherence is bounded between [0, 1], where 1 indicates perfect phase alignment. Some delayed coherence is noted in the γ frequency range. Inset, Spectrogram of trill vocalization; y scale, 0-25 kHz; x scale, 600 ms. B, Plot of the peak coherence in the γ-frequency range over time (blue), for the example in A. Results are compared with similar coherence analysis for the MUA (black) and phase-removed LFP power (green), showing similar though weaker trends. C, Scatter plot comparing coherence in γ frequencies with that of the MUA and LFP power across the population, suggesting much of the apparent coherence in γ oscillations may have been due to the coherence in the overall response power, rather than the oscillations themselves. D, Sample PSTH of total and induced γ responses aligned by vocal onset (black/blue), and recalculated by aligning to the times of the first, second, and third frequency modulation peaks of trill vocalization acoustics. Solid lines indicate realigned evoked responses. Dashed lines indicate induced responses. There was a slight reduction in the average induced response (13%–17%). Onset peaks are seen for induced responses here due to phase alignment to trill oscillations rather than onset. E, Population histogram showing changes in total (black) and induced (blue) γ power during peak realignment versus onset alignment, showing only small changes in induced power (2.6% decrease). F, Sample unit γ response to phee vocalizations, which do not contain any frequency modulated acoustics, showing similar total and induced γ activity. Inset, Spectrogram of phee vocalization, y scale, 0–25 kHz; x scale, 2200 ms. G, Population histograms for γ responses to phee vocalization production (left) and playback (right). Total (black) and induced (blue) phee responses are shown; also shown are total γ responses to trill vocalizations for these same sites (green). Overall γ activity for these sites was weak, but stronger for phees than for trills (trills decreased p < 0.001, total and induced phee unchanged from prevocal: p = 0.25 and p = 0.38). During playback, phees evoked strong total γ power, though weaker than for trills (all p < 0.001).