Thalamocortical Architecture of a Visual Cortex Without Orientation Columns

描述(由申请人提供)：拟议工作的一个主要目标是更好地了解丘脑皮质对兔视觉皮质(V1)神经元的输入如何有助于合成在V1输入层中看到的各种感受场属性。在两个层中 4和6，它们包括(A)具有高度定向和定向感受区的“简单”细胞，这些细胞由分开的平行的ON和/或OFF亚区组成，以及(B)假定的快速峰抑制中间神经元(SINS)具有重叠的ON-OFF，即缺乏显著方向/方向选择性的接受区。虽然关于猫V1层简单细胞的这些问题已经做了大量的工作，但关于兔子和啮齿类动物V1层的感受野合成以及丘脑皮质对这种合成的贡献的性质，人们知之甚少。兔子和啮齿类动物的V1与肉食动物和灵长类动物的V1相似，因为它们有许多对视觉刺激的方向具有高度选择性的“简单”细胞。然而，与食肉动物和灵长类动物不同， 兔子和啮齿动物缺乏定向柱。此外，它们的视觉丘脑(LGN)含有直接向V1提供方向和方位信息的神经元。在猫和灵长类动物中，定向和定向选择性被认为是在V1中合成的，而在兔子和啮齿动物中，这些特性可能是从丘脑继承的。建议的实验将直接解决这个问题，在第4层和第6层。我们将记录清醒兔LGN中不同类型的细胞，其中一些具有定向和/或定向选择性感受场。我们将从输入层(4和6)中的简单单元格和SINS同时进行记录，简单单元格的方向/方向被高度调整，SINS的调谐性很差。我们将使用相互关联的方法来了解哪些LGN细胞与哪些皮质细胞进行功能性接触。我们的初步结果表明，第四层简单细胞不继承LGN定向选择神经元的定向/定向偏好。因此，L4层简单细胞的取向偏好很大程度上可能是由ON和OFF LGN传入的感受野排列造成的，就像猫一样。或者，它可以从具有显示取向偏差的同心接受场的LGN输入继承而来。通过测量L4皮层LGN输入的感受场特性 简单的细胞，我们的实验将能够区分这两种可能的机制。

DESCRIPTION (provided by applicant): A major goal of the proposed work is to better understand how thalamocortical inputs to rabbit visual cortical (V1) neurons contribute to the synthesis of the diverse receptive fields properties seen in the input layers of V1. In both layers 4 and 6, these include (a) "simple" cells with highly oriented and directional receptive fields composed of separate parallel ON and/or OFF sub-zones, and (b) putative fast spike inhibitory interneurons (SINs) with overlapping ON-OFF, receptive fields that lack significant orientation/direction selectivity. While considerable work has been done on these questions for simple cells in layer 4 of feline V1, little is known about receptive field synthesis in V1 of rabbts and rodents, and the nature of the thalamocortical contribution to this synthesis. V1 of rabbits and rodents is similar to that of carnivores and primates in having many "simple" cells that are highly selective for the orientation of a visual stimulus. However, unlike carnivores and primates, rabbits and rodents lack orientation columns. Moreover, their visual thalamus (LGN) contains neurons that provide directional and orientation information directly to V1. Whereas in cats and primates, orientation and directional selectivity are thought to be synthesized within V1, in rabbits and rodents these properties could potentially be inherited from the thalamus. The proposed experiments will address this question directly, in both layers 4 and 6. We will record from different cell types in the LGN of awake rabbits, some of which have directional and or orientation selective receptive fields. We will make simultaneous recordings from simple cells and SINs in the input layers (4 and 6), the simple cells being highly tuned for orientation/direction, the SINs being poorly tuned. We will use cross-correlation methods to see which LGN cells make functional contacts with which cortical cells. Our preliminary results suggest that layer 4 simple cells do not inherit their orientation/directional preference from LGN directional selective neurons. Therefore, the orientation preference of layer 4 simple cells may be largely created from the receptive field arrangement of ON and OFF LGN afferents, as in the cat. Alternatively, it may be inherited from LGN inputs with concentric receptive fields that show an orientation bias. By measuring the receptive field properties of the LGN inputs to a L4 cortical simple cell, our experiments will be able to distinguish between these two possible mechanisms.