Title: Song Decrystallization in Adult Zebra Finches Does Not Require the Song Nucleus 1

35 In adult male zebra finches, transecting the vocal nerve causes previously stable (i.e., 36 crystallized) song to slowly degrade, presumably because of the resulting distortion in 37 auditory feedback. How and where distorted feedback interacts with song motor 38 networks to induce this process of song decrystallization remains unknown. The song 39 premotor nucleus HVC is a potential site where auditory feedback signals could interact 40 with song motor commands. Although the forebrain nucleus NIf appears to be the 41 primary auditory input to HVC, NIf lesions made in adult zebra finches do not trigger 42 song decrystallization. One possibility is that NIf lesions do not interfere with song 43 maintenance, but do compromise the adult zebra finch’s ability to express renewed vocal 44 plasticity in response to feedback perturbations. To test this idea, we bilaterally lesioned 45 NIf and then transected the vocal nerve in adult male zebra finches. We found that 46 bilateral NIf lesions did not prevent nerve section-induced song decrystallization. To test 47 the extent to which the NIf lesions disrupted auditory processing in the song system, we 48 made in vivo extracellular recordings in HVC and a downstream anterior forebrain 49 pathway (or AFP) in NIf-lesioned birds. We found strong and selective auditory 50 responses to the playback of the birds’ own song (BOS) persisted in HVC and the AFP 51 following NIf lesions. These findings suggest that auditory inputs to the song system 52 other than NIf, such as the caudal mesopallium (CM) could act as source of auditory 53 feedback signals to the song motor network. 54 55