Brandner S, Redies H
Department of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Federal Republic of Germany.
J Neurosci. 1990 Jan;10(1):50-61. doi: 10.1523/JNEUROSCI.10-01-00050.1990.
The topography of the anatomical projection from isofrequency contours (IFCs) in auditory thalamus to IFCs in primary auditory cortex (field AI) was investigated in the cat. In each experiment, a best-frequency map of AI was obtained with electrophysiological recording techniques. Then, different retrogradely transported tracers (HRP, fluorescent dyes) were introduced into AI. In some experiments, different parts (e.g., dorsal, central, and ventral) of a previously mapped IFC were injected, each part with a different tracer. In other experiments, 2 or 3 rows of tracer injections were made at different dorsoventral levels of AI, over a large frequency range (5-38 kHz); each injection row was oriented orthogonal to the IFCs and contained a different tracer. The main mass of the labeled thalamic cells was found in the ventral nucleus of the medial geniculate body (MGv). The MGv cells projecting to a limited sector (1-2 mm in length in most experiments) of an IFC in AI form one or several densely packed neuron clusters of variable shape. The cells labeled by a given tracer are largely separated in space from cells labeled by a different tracer. Thus, different sectors of a cortical IFC receive input from different portions of the corresponding thalamic IFC. As a general rule, cells labeled from dorsal (ventral) injections are centered rostrally (caudally) in the part of MGv innervating AI. However, the topographic details are variable between individuals, and the rostrocaudal gradient is complicated by numerous irregularities and gradients. Previous studies of the auditory thalamocortical projection in the cat have not recognized the topographic order in the isofrequency dimension. Instead, it was believed that different sectors of a cortical IFC were innervated by coincident thalamic populations.
在猫身上研究了听觉丘脑等频率轮廓（IFC）到初级听觉皮层（AI区）IFC的解剖投射地形图。在每个实验中，用电生理记录技术获得AI区的最佳频率图。然后，将不同的逆行运输示踪剂（辣根过氧化物酶、荧光染料）注入AI区。在一些实验中，向先前绘制的IFC的不同部分（如背侧、中央和腹侧）注射，每个部分使用不同的示踪剂。在其他实验中，在AI区不同的背腹水平上，在较大的频率范围（5 - 38千赫）内进行2或3排示踪剂注射；每排注射与IFC正交，且含有不同的示踪剂。标记的丘脑细胞主要集中在内侧膝状体腹侧核（MGv）。投射到AI区IFC有限扇区（大多数实验中长度为1 - 2毫米）的MGv细胞形成一个或几个形状各异、紧密排列的神经元簇。由给定示踪剂标记的细胞在空间上与由不同示踪剂标记的细胞大多是分开的。因此，皮层IFC的不同扇区从相应丘脑IFC的不同部分接收输入。一般来说，从背侧（腹侧）注射标记的细胞在支配AI区的MGv部分中位于嘴侧（尾侧）中心。然而，个体之间的地形细节存在差异，并且前后梯度因众多不规则性和梯度而变得复杂。先前对猫听觉丘脑皮质投射的研究没有认识到等频率维度中的地形顺序。相反，人们认为皮层IFC的不同扇区由重合的丘脑群体支配。
