Fig. 6. In zebra finch Y34, air sac pressure was reduced uniformly throughout expiratory pulses, but airflow reduction increased at the end of pulses. The top panel shows the air sac pressure traces for the two syllables (P) of the motif for pre-injection (blue), one injection (red) and two injections (green), with the percent reduction from pre-injection for each injection trace indicating a fairly uniform reduction. Cumulative airflow for each syllable (bottom panel; shown as cumulative flow) indicates not only the overall decrease in flow after injections but also that, at the end of syllables, increases in airflow present in pre-injection song cannot be sustained by the injected bird (change in slope marked by arrows).