Johnson F, Sablan M M, Bottjer S W
Department of Biological Sciences, University of Southern California, Los Angeles 90089-2520, USA.
J Comp Neurol. 1995 Jul 24;358(2):260-78. doi: 10.1002/cne.903580208.
A serial pathway from a thalamic nucleus (DLM; the medial portion of the dorsolateral nucleus of the anterior thalamus) to a cortical region (lMAN; the lateral magnocellular nucleus of the anterior neostriatum) to a motor-cortical region (RA; the robust nucleus of the archistriatum) is necessary for vocal production during song learning in juvenile zebra finches but not for the recitation of a song already learned by adults. To obtain new information about the possible function of the DLM-->lMAN-->RA pathway in vocal learning, we used anterograde and retrograde tract-tracing techniques (pressure injections of DiI and DiA) to map the pattern of axonal connections between these brain regions in adult male zebra finches. Results revealed two topographically organized pathways that traverse the songbird forebrain in parallel. An oval-shaped dorsal/lateral portion of DLM projects solely to the central core of lMAN (lMANcore), whereas a crescent-shaped region, including ventral and medial DLM, projects exclusively to a parvicellular shell that encircles lMANcore (lMANshell). In turn, lMANshell neurons project solely to an arc-shaped region of dorsal archistriatum just lateral to RA (Ad; archistriatum, pars dorsalis), whereas lMANcore neurons project exclusively to RA. We also identified crossed and reciprocal pathways between lMANcore/shell and the lateral portion of the ventral archistriatum, which may contribute to interhemispheric coordination of vocal behavior. A robust topographic organization was observed in the axonal projections from dorsal/lateral-DLM-->lMANcore-->RA and from ventral/medial-DLM-->lMANshell-->Ad, raising the question of what is being mapped within these two forebrain pathways. Because RA projection neurons are organized myotopically with respect to the major vocal (syringeal) muscles (D.S. Vicario, 1991, J. Comp. Neurol. 309:486-494), one possibility is that a mapping of vocal/expiratory musculature is preserved "upstream" within these pathways. Similarly, the presence of song-selective auditory neurons in DLM, lMAN, and RA (A.J. Doupe and M. Konishi, 1991, Soc. Neurosci. Abstr. 18:527) suggests that these pathways might subserve some form of auditory or auditory-motor mapping.
在幼年斑胸草雀学习鸣叫的过程中，从丘脑核（丘脑背外侧核内侧部分；DLM）到皮质区域（新纹状体前部外侧大细胞核；lMAN）再到运动皮质区域（古纹状体粗核；RA）的一系列神经通路对于发声是必需的，但对于成年斑胸草雀背诵已学歌曲则并非必需。为了获取有关DLM→lMAN→RA通路在发声学习中可能功能的新信息，我们使用了顺行和逆行示踪技术（压力注射DiI和DiA）来描绘成年雄性斑胸草雀这些脑区之间的轴突连接模式。结果揭示了两条在鸣禽前脑平行穿过的具有拓扑结构的通路。DLM的椭圆形背侧/外侧部分仅投射到lMAN的中央核心（lMANcore），而包括腹侧和内侧DLM的新月形区域则专门投射到环绕lMANcore的小细胞壳层（lMANshell）。反过来，lMANshell神经元仅投射到RA外侧背侧古纹状体的弧形区域（Ad；古纹状体背侧部），而lMANcore神经元仅投射到RA。我们还确定了lMANcore/壳层与腹侧古纹状体外侧部分之间的交叉和相互通路，这可能有助于发声行为的半球间协调。在从背侧/外侧-DLM→lMANcore→RA和从腹侧/内侧-DLM→lMANshell→Ad的轴突投射中观察到了强大的拓扑结构，这就引发了一个问题，即在这两条前脑通路中映射的是什么。由于RA投射神经元在主要发声（鸣管）肌肉方面是按肌区定位组织的（D.S.维卡里奥，1991年，《比较神经学杂志》309:486 - 494），一种可能性是在这些通路“上游”保留了发声/呼气肌肉组织的映射。同样，在DLM、lMAN和RA中存在对歌曲有选择性的听觉神经元（A.J.杜普和M.小西，1991年，《神经科学学会摘要》18:527）表明这些通路可能服务于某种形式的听觉或听觉 - 运动映射。
