Jeffs Janelle, Federer Frederick, Angelucci Alessandra
Department of Ophthalmology and Visual Science,Moran Eye Institute,University of Utah,Salt Lake City,Utah 84132.
Vis Neurosci. 2015 Jan;32:E012. doi: 10.1017/S0952523815000097.
The organization of the cortex located immediately anterior to the second visual area (V2), i.e., the third tier visual cortex, remains controversial, especially in New World primates. In particular, there is lack of consensus regarding the exact location and extent of the lower visual quadrant representation of the third visual area V3 (or ventrolateral posterior -VLP - of a different nomenclature). Microelectrode and connectional mapping studies have revealed the existence of an upper visual quadrant representation abutting dorsal V2 anteriorly, and bordered medially and laterally by representations of the lower visual quadrant. It remains unclear whether these lower field regions are both part of a single area V3, which is split into two patches by an interposed region of upper field representation, or whether they are the lower field representations of two different areas, the dorsomedial area (DM) and area V3/VLP, respectively. To address this question, we quantitatively analyzed the patterns of corticocortical afferent connections labeled by tracer injections targeted to these two lower field regions in the dorsal aspect of the third tier cortex. We found different inter-areal connectivity patterns arising from these two regions, strongly suggesting that they belong to two different visual areas. In particular, our results indicate that the dorsal aspect of the third tier cortex consists of two distinct areas: a full area DM, representing the lower quadrant medially, and the upper quadrant laterally, and the lower quadrant representation of V3/VLP, located laterally to upper field DM. DM is predominantly connected with areas of the dorsal visual stream, and V3/VLP with areas of the ventral stream. These results prompt further functional investigations of the third tier cortex, as previous studies of this cortical territory may have pooled response properties of two very different areas into a single area V3.
紧邻第二视觉区（V2）前方的皮质组织，即第三层视觉皮质，其组织结构仍存在争议，在新大陆灵长类动物中尤为如此。特别是，关于第三视觉区V3（或不同命名法中的腹外侧后区-VLP-）在下视觉象限的精确位置和范围，目前尚无共识。微电极和连接图谱研究揭示了在背侧V2前方存在一个上视觉象限表征，其内侧和外侧由下视觉象限表征界定。目前尚不清楚这些下视野区域是属于单个区域V3的一部分，该区域被上视野表征的插入区域分成两个斑块，还是它们分别是两个不同区域，即背内侧区（DM）和V3/VLP区的下视野表征。为了解决这个问题，我们定量分析了通过向第三层皮质背侧的这两个下视野区域注射示踪剂标记的皮质皮质传入连接模式。我们发现这两个区域产生了不同的区域间连接模式，强烈表明它们属于两个不同的视觉区域。特别是，我们的结果表明，第三层皮质的背侧由两个不同的区域组成：一个完整的DM区域，在内侧代表下象限，在外侧代表上象限，以及V3/VLP的下象限表征，位于上视野DM的外侧。DM主要与背侧视觉流区域相连，而V3/VLP与腹侧流区域相连。这些结果促使对第三层皮质进行进一步的功能研究，因为此前对该皮质区域的研究可能将两个非常不同区域的反应特性汇总到了单个区域V3中。
