Thalamocortical Architecture of a Visual Cortex Without Orientation Columns

描述（由申请人提供）：所提出的工作的一个主要目标是更好地了解丘脑皮质输入到兔视觉皮层（V1）神经元如何有助于合成V1输入层中看到的各种感受野特性。在两个层中 如图4和6所示，这些包括（a）具有由独立的平行ON和/或OFF子区组成的高度定向和方向性感受野的“简单”细胞，和（B）具有重叠的ON-OFF感受野的推定的快速尖峰抑制性中间神经元（SIN），其缺乏显著的定向/方向选择性。虽然相当多的工作已经完成了这些问题的简单细胞在第4层的猫V1，很少有人知道感受野合成V1的兔子和啮齿动物，以及丘脑皮质的贡献，这种合成的性质。兔子和啮齿动物的V1与食肉动物和灵长类动物的V1相似，都有许多“简单”细胞，对视觉刺激的方向具有高度选择性。然而，与食肉动物和灵长类动物不同， 兔子和啮齿类动物缺少方向柱。此外，他们的视觉丘脑（LGN）包含直接向V1提供方向和方向信息的神经元。在猫和灵长类动物中，方向和方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遗传的。所提出的实验将在第4层和第6层中直接解决这个问题。我们将记录不同类型的细胞在LGN清醒的兔子，其中一些具有方向和/或方向选择性感受野。我们将从输入层（4和6）中的简单细胞和SIN进行同时记录，简单细胞针对取向/方向被高度调谐，SIN被不良调谐。我们将使用交叉相关方法来观察哪些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4层简单细胞不继承他们的方向/方向偏好LGN方向选择性神经元。因此，第4层简单细胞的取向偏好可能主要是从ON和OFF LGN传入的感受野排列中产生的，就像猫一样。或者，它可能是从具有同心感受野的LGN输入中继承的，这些感受野显示出取向偏好。通过测量LGN输入到L4皮层的感受野特性， 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.