Hackett T A, Stepniewska I, Kaas J H
Department of Psychology, Vanderbilt University, Nashville, Tennessee 37240, USA.
J Comp Neurol. 1998 Oct 19;400(2):271-86. doi: 10.1002/(sici)1096-9861(19981019)400:2<271::aid-cne8>3.0.co;2-6.
The auditory cortex of macaque monkeys contains a core of primary-like areas surrounded by a narrow belt of associated fields that encompass much of the superior temporal plane in these animals. Adjacent to the lateral belt on the superior temporal gyrus is a parabelt region that contains at least two subdivisions (rostral and caudal). In a previous study (Hackett et al. [1998] J. Comp. Neurol. 394:475-495), we determined that the parabelt has topographic connections with the belt areas surrounding the core, but minimal connections with the core itself. In this study, we describe the thalamocortical connections of the parabelt auditory cortex based on multiple injections of neuronal tracers into this region in each of five macaque monkeys. Injections confined to the parabelt labeled large numbers of neurons in the dorsal (MGd) and magnocellular (MGm) divisions of the medial geniculate complex (MGC), suprageniculate (Sg), limitans (Lim), and medial pulvinar (PM) nuclei. Only when injections encroached on the lateral belt cortex were substantial numbers of labeled neurons found in the ventral (MGv) division of the MGC, consistent with the absence of significant connections between the parabelt and core fields. The rostrocaudal topography of the parabelt region was maintained in the thalamocortical connections, supporting the parcellation of this region of cortex. The results suggest that the parabelt region represents a third level of auditory cortical processing, which is not influenced by direct inputs from primary cortical or subcortical auditory structures.
猕猴的听觉皮层包含一个类似初级区域的核心，其周围是一条狭窄的关联区域带，该区域带覆盖了这些动物大部分的颞上平面。颞上回外侧带相邻的是一个旁带区域，该区域至少包含两个亚区（吻侧和尾侧）。在之前的一项研究（哈克特等人，[1998]《比较神经学杂志》394:475 - 495）中，我们确定旁带与围绕核心的带状区域有拓扑连接，但与核心本身的连接极少。在本研究中，我们基于向五只猕猴中的每只猕猴该区域多次注射神经元示踪剂，描述了旁带听觉皮层的丘脑皮质连接。局限于旁带的注射标记了内侧膝状体复合体（MGC）的背侧（MGd）和大细胞（MGm）部分、上膝状体（Sg）、界限核（Lim）以及内侧丘脑枕（PM）核中的大量神经元。只有当注射侵入外侧带皮层时，才在MGC的腹侧（MGv）部分发现大量标记神经元，这与旁带和核心区域之间缺乏显著连接一致。旁带区域的吻尾拓扑结构在丘脑皮质连接中得以保留，支持了该皮层区域的分区。结果表明，旁带区域代表了听觉皮层处理的第三个层次，不受来自初级皮层或皮层下听觉结构的直接输入影响。
