Abstract
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.
Highlights
Lateralized behaviors are controlled preferentially by one side of the body
Animals and Recording Procedures Nineteen adult male Bengalese finches were used in this study
The most pronounced differences in the spectral features of the Bengalese finch song were observed following resection of the left NXIIts nerve, whereas right side nerve resection resulted in more modest changes in spectral features of song syllables
Summary
Lateralized behaviors are controlled preferentially by one side of the body. It was once thought that lateralization of function only occurred in humans, but it is known that the control of complex, learned behaviors is specialized to one side of the body in diverse species including fish, parrots, crows, rodents and chimpanzees [1,2,3,4]. When compared to the right hemisphere, the cortical areas controlling language production and comprehension are larger and during speech production are more active on the left side of the brain [6,7]. This lateralization is observed in congenitally deaf children exposed to early sign language, suggesting that hemispheric specialization is tied to language and not just speech production [8]. 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). How the left and right sides of the syrinx contribute to acoustic control of song has not been studied
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