Syringeal Specialization of Frequency Control during Song Production in the Bengalese Finch (Lonchura striata domestica)

BackgroundSinging in songbirds is a complex, learned behavior which shares many parallels with human speech. The avian vocal organ (syrinx) has two potential sound sources, and each sound generator is under unilateral, ipsilateral neural control. Different songbird species vary in their use of bilateral or unilateral phonation (lateralized sound production) and rapid switching between left and right sound generation (interhemispheric switching of motor control). Bengalese finches (Lonchura striata domestica) have received considerable attention, because they rapidly modify their song in response to manipulations of auditory feedback. However, how the left and right sides of the syrinx contribute to acoustic control of song has not been studied. MethodologyThree manipulations of lateralized syringeal control of sound production were conducted. First, unilateral syringeal muscular control was eliminated by resection of the left or right tracheosyringeal portion of the hypoglossal nerve, which provides neuromuscular innervation of the syrinx. Spectral and temporal features of song were compared before and after lateralized nerve injury. In a second experiment, either the left or right sound source was devoiced to confirm the role of each sound generator in the control of acoustic phonology. Third, air pressure was recorded before and after unilateral denervation to enable quantification of acoustic change within individual syllables following lateralized nerve resection. SignificanceThese experiments demonstrate that the left sound source produces louder, higher frequency, lower entropy sounds, and the right sound generator produces lower amplitude, lower frequency, higher entropy sounds. The bilateral division of labor is complex and the frequency specialization is the opposite pattern observed in most songbirds. Further, there is evidence for rapid interhemispheric switching during song production. Lateralized control of song production in Bengalese finches may enhance acoustic complexity of song and facilitate the rapid modification of sound production following manipulations of auditory feedback.背景 鸣禽的鸣唱发声是一种复杂的习得性行为，与人类言语存在诸多共通特征。鸟类的发声器官——鸣管（syrinx）拥有两处潜在声源，且每个发声器均接受单侧、同侧的神经支配。不同鸣禽物种在双侧或单侧发声（偏侧发声，lateralized sound production）的应用，以及左右发声结构间的快速切换（运动控制的跨半球切换，interhemispheric switching of motor control）方面存在差异。孟加拉文鸟（Bengalese finch，Lonchura striata domestica）已受到广泛关注，因其可在听觉反馈被操控后快速调整自身鸣唱。然而，鸣管左右两侧如何参与鸣唱的声学调控，目前尚未得到研究。 研究方法 本研究开展了三项针对发声控制偏侧化的操控实验。首先，通过切除支配鸣管神经肌肉的舌下神经（hypoglossal nerve）气管鸣管支（tracheosyringeal portion），消除单侧鸣管肌肉的神经支配。随后对比偏侧化神经损伤前后鸣唱的频谱与时域特征。第二项实验中，对左侧或右侧声源进行消声处理，以验证各发声器在声学发声调控中的作用。第三项实验中，在单侧去神经支配前后记录气道压力，以量化偏侧神经切除后单个鸣唱音节的声学变化。 研究意义 本实验证实，左侧声源可产生响度更高、频率更高、熵值更低的鸣唱音节，而右侧发声器则产生振幅更低、频率更低、熵值更高的鸣唱音节。双侧发声的分工模式较为复杂，其频率特化模式与多数鸣禽恰好相反。此外，实验结果为鸣唱过程中存在快速跨半球切换提供了证据。孟加拉文鸟鸣唱的偏侧化控制，或可提升鸣唱的声学复杂度，并助力其在听觉反馈被操控后快速调整发声行为。