Department of Biology, University of Utah, Salt Lake City, Utah 84112, USA.
J Neurosci. 2010 Oct 6;30(40):13246-53. doi: 10.1523/JNEUROSCI.1130-10.2010.
Like human infants, songbirds acquire their song by imitation and eventually generate sounds that result from complicated neural networks and intrinsically nonlinear physical processes. Signatures of low-dimensional chaos such as subharmonic bifurcations have been reported in adult and developing zebra finch song. Here, we use methods from nonlinear dynamics to test whether adult male zebra finches (Taenopygia guttata) use the intrinsic nonlinear properties of their vocal organ, the syrinx, to insert subharmonic transitions in their song. In contrast to previous data on the basis of spectrographic evidence, we show that subharmonic transitions do not occur in adult song. Subharmonic transitions also do not arise in artificially induced sound in the intact syrinx, but are commonly generated in the excised syrinx. These findings suggest that subharmonic transitions are not used to increase song complexity, and that the brain controls song in a surprisingly smooth control regimen. Fast, smooth changes in acoustic elements can be produced by direct motor control in a stereotyped fashion, which is a more reliable indicator of male fitness than abrupt acoustic changes that do not require similarly precise control. Consistent with this view is the presence of high fidelity at every level of motor control, from telencephalic premotor areas to superfast syringeal muscles.
与人类婴儿一样，鸣禽通过模仿来学习它们的歌曲，最终产生的声音源自复杂的神经网络和内在的非线性物理过程。亚谐波分岔等低维混沌特征已经在成年和发育中的斑马雀歌声中被报道。在这里，我们使用非线性动力学的方法来检验成年雄性斑马雀（Taenopygia guttata）是否利用其鸣管（syrinx）的内在非线性特性来插入其歌声中的亚谐波跃迁。与基于光谱证据的先前数据相反，我们表明成年歌声中不会发生亚谐波跃迁。亚谐波跃迁也不会出现在完整鸣管中的人工诱导声音中，但在切除的鸣管中很常见。这些发现表明，亚谐波跃迁不是用来增加歌曲复杂性的，大脑以一种惊人的平滑控制方案控制着歌曲。通过直接的肌肉控制可以以刻板的方式产生声音元素的快速、平滑变化，这比不需要类似精确控制的突然的声音变化更能可靠地指示雄性的适应能力。与这一观点一致的是，从端脑运动前区到超快鸣管肌肉，在运动控制的每一个层面都存在着高度的保真度。
