Birdsong production requires a precise control of the respiratory system and muscles in the syrinx, the avian vocal organ. Oscine birds use a set of highly developed neural nuclei which produce precise patterns of activity to achieve this. Interestingly, these patterns have been shown to occur spontaneously during sleep. Even more, while the respiratory pathway is blocked during sleep (and thus birds don’t sleep-sing), the pathway innervating the syrinx is not, and this activity arrives at the muscles, making the periphery a window into the sleeping brain.
In tyrannid suboscine birds (phylogenetically close to oscine birds, usually considered non-learners) such developed neural nuclei haven´t been found, thus making this window a unique tool to study sleep in the non-learning brain.
In this work we study the suboscine Pitangus Sulphuratus. We focus on the obliquus ventralis, a muscle involved in the amplitude modulation of sound during song. We show that events of song-like activity occur during sleep, as in the case of oscine birds. This activity is consistent with the rehearsal of the song, or part of it, and has some variability not observed during wake. We also find a set of qualitatively different events, compatible with another vocalization, usually produced during territorial dispute and accompanied by a behavioral display. Using recordings of the sleeping bird we show that the activity is consistently produced during sleep simultaneously with the behavioral display.