Journal of Neuroscience, Vol 6, 3595-3610, Copyright © 1986 by Society for Neuroscience
Bilateral syringeal coupling during phonation of a songbird
S Nowicki and RR Capranica
The syrinx of oscine birds ("true songbirds") is a double vocal organ, and
each side has generally been presumed to function independently under
separate neural control during phonation. A significant counterexample is
demonstrated here in the production of a common vocalization by the
black-capped chickadee (Parus atricapillus), in which the 2 acoustic
sources of the syrinx interact in a nonlinear fashion. The chickadee
produces a sound with multiple frequency components that superficially
resemble harmonics. An analysis of vocal production after unilateral and
bilateral syringeal denervation shows instead that these frequency
components are sum and difference frequencies, or heterodyne frequencies,
resulting from cross-modulation between the 2 syringeal sides. A limited
form of this bilateral coupling may be achieved after unilateral
denervation of either syringeal side but not after bilateral denervation.
Unilaterally denervated birds are capable of significant improvement in
coupling after 10 d, too short a period for neural regrowth. These results
suggest that coupling arises from a passive physical interaction between
the 2 syringeal sources which is activated or regulated in some fashion by
neural control from either side.