Striedter G F
Division of Biology, California Institute of Technology, Pasadena 91125.
J Comp Neurol. 1994 May 1;343(1):35-56. doi: 10.1002/cne.903430104.
Previous studies concluded that parrots and oscine songbirds, two taxa that have independently evolved the ability to learn vocalizations, possess similar neural circuits for vocal control. These investigations suggested, however, that the vocal control systems of parrots and songbirds may also differ in several respects. Most importantly, auditory inputs to the vocal control system derive from Field L in songbirds, but this area does not appear to project to the vocal control system in parrots. The principal aims in the present study were, therefore, to determine 1) exactly how similar the vocal control system in budgerigars is to that in songbirds and 2) whether the vocal control system in budgerigars receives auditory inputs from areas other than Field L. Biotinylated and fluorescently labeled dextrans were injected into five telencephalic nuclei of the vocal control system in budgerigars and into the physiologically identified auditory portions of the frontal neostriatum and nucleus basalis. The results indicate that the forebrain vocal control system in budgerigars is only superficially similar to that in songbirds. Many of the vocal control nuclei differ between the two taxa in both cytoarchitecture and connections. The nuclei in budgerigars that are comparable to those of the accessory loop of the vocal control system in songbirds, for example, do not form an accessory loop in budgerigars. The vocal control systems in the two taxa differ most significantly in the source of their auditory inputs. In songbirds, auditory information is conveyed to the vocal control system via Field L, whereas, in budgerigars, the auditory inputs to the vocal control system derive from nucleus basalis and the frontal neostriatum. A phylogenetic analysis suggests that the midbrain and medullary vocal control pathways are homologous across all birds, but that most of the vocal control circuits in the forebrain have probably evolved independently in parrots and songbirds.
以往的研究得出结论，鹦鹉和鸣禽这两个独立进化出学习发声能力的类群，拥有相似的用于发声控制的神经回路。然而，这些研究表明，鹦鹉和鸣禽的发声控制系统在几个方面也可能存在差异。最重要的是，发声控制系统的听觉输入来自鸣禽的L区，但这个区域在鹦鹉中似乎并不投射到发声控制系统。因此，本研究的主要目的是确定：1）虎皮鹦鹉的发声控制系统与鸣禽的发声控制系统究竟有多相似；2）虎皮鹦鹉的发声控制系统是否从L区以外的区域接收听觉输入。将生物素化和荧光标记的葡聚糖注射到虎皮鹦鹉发声控制系统的五个端脑核以及额叶新纹状体和基底核的生理确定的听觉部分。结果表明，虎皮鹦鹉的前脑发声控制系统与鸣禽的仅表面相似。这两个类群的许多发声控制核在细胞结构和连接方面都有所不同。例如，虎皮鹦鹉中与鸣禽发声控制系统副环相当的核，在虎皮鹦鹉中并不形成副环。这两个类群的发声控制系统在听觉输入来源上差异最为显著。在鸣禽中，听觉信息通过L区传递到发声控制系统，而在虎皮鹦鹉中，发声控制系统的听觉输入来自基底核和额叶新纹状体。系统发育分析表明，中脑和延髓的发声控制通路在所有鸟类中是同源的，但前脑中的大多数发声控制回路可能在鹦鹉和鸣禽中独立进化。
