Fitzgibbon Thomas, Szmajda Brett A, Martin Paul R
Discipline of Anatomy & Histology, School of Medical Sciences and Bosch Institute, University of Sydney, Sydney, NSW 2006 Australia.
Vis Neurosci. 2007 Nov-Dec;24(6):857-74. doi: 10.1017/S0952523807070770.
The thalamic reticular nucleus (TRN) supplies an important inhibitory input to the dorsal thalamus. Previous studies in non-primate mammals have suggested that the visual sector of the TRN has a lateral division, which has connections with first-order (primary) sensory thalamic and cortical areas, and a medial division, which has connections with higher-order (association) thalamic and cortical areas. However, the question whether the primate TRN is segregated in the same manner is controversial. Here, we investigated the connections of the TRN in a New World primate, the marmoset (Callithrix jacchus). The topography of labeled cells and terminals was analyzed following iontophoretic injections of tracers into the primary visual cortex (V1) or the dorsal lateral geniculate nucleus (LGNd). The results show that rostroventral TRN, adjacent to the LGNd, is primarily connected with primary visual areas, while the most caudal parts of the TRN are associated with higher order visual thalamic areas. A small region of the TRN near the caudal pole of the LGNd (foveal representation) contains connections where first (lateral TRN) and higher order visual areas (medial TRN) overlap. Reciprocal connections between LGNd and TRN are topographically organized, so that a series of rostrocaudal injections within the LGNd labeled cells and terminals in the TRN in a pattern shaped like rostrocaudal overlapping "fish scales." We propose that the dorsal areas of the TRN, adjacent to the top of the LGNd, represent the lower visual field (connected with medial LGNd), and the more ventral parts of the TRN contain a map representing the upper visual field (connected with lateral LGNd).
丘脑网状核（TRN）向背侧丘脑提供重要的抑制性输入。以往在非灵长类哺乳动物中的研究表明，TRN的视觉部分有一个外侧部，它与一级（初级）感觉丘脑和皮质区域有联系，还有一个内侧部，它与高级（联合）丘脑和皮质区域有联系。然而，灵长类动物的TRN是否以同样的方式分隔仍存在争议。在这里，我们研究了一种新大陆灵长类动物狨猴（Callithrix jacchus）的TRN的连接。在将示踪剂离子电渗注入初级视觉皮层（V1）或背侧外侧膝状体核（LGNd）后，分析了标记细胞和终末的拓扑结构。结果表明，与LGNd相邻的吻腹侧TRN主要与初级视觉区域相连，而TRN最尾端的部分与高级视觉丘脑区域相关。LGNd尾极附近的一小部分TRN（中央凹代表区）包含一级（外侧TRN）和高级视觉区域（内侧TRN）重叠的连接。LGNd和TRN之间的相互连接在拓扑上是有组织的，因此在LGNd内进行的一系列吻尾侧注射会以一种类似吻尾侧重叠“鱼鳞”的模式标记TRN中的细胞和终末。我们提出，与LGNd顶部相邻的TRN背侧区域代表下部视野（与内侧LGNd相连），而TRN更腹侧的部分包含一个代表上部视野的图谱（与外侧LGNd相连）。
