Spatio-temporal dynamics of feedforward and feedback processing in the visual thalamo-cortico-thalamic loop

在教科书中，视觉系统通常被描绘成由层次结构排列并通过前馈投影连接的处理阶段组成。然而，更详细地考虑视觉系统的解剖结构，很明显，前馈投影的数量往往远远超过反馈投影。这一一般规则也适用于丘脑的背外侧膝状体核（dLGN），其中~30%的传递给中继细胞的突触输入是由皮质丘脑（CT）锥体细胞产生的，而只有~10%的突触输入是由视网膜神经节细胞产生的前馈输入。如何这个解剖学上大规模的反馈投射到最早的视觉处理阶段之一的影响表示在dLGN和影响计算在丘脑皮层回路迄今仍不完全understood.The拟议的研究是一个后续项目，继续围绕皮质丘脑反馈信息处理在早期视觉系统的影响为中心。虽然我们在上一个资助期的研究提供了深入了解丘脑中CT反馈回路的视网膜组织和CT反馈效应在塑造空间处理中的双重性质，即促进和抑制，但我们这项后续建议的中心目标是阐明丘脑-皮质-丘脑相互作用中前馈和反馈处理的时空动力学。特别地，我们将（1）分离CT反馈在dLGN和visTRN中的时间影响，我们将（2）通过使用CT反馈终端的路径特异性光遗传抑制以及来自丘脑和皮层的同时记录来研究CT反馈在塑造时空选择性中的作用，并且我们将（3）探索CT反馈在丘脑皮质节律和通信中的作用。本研究有望有助于回答直接兴奋性和间接抑制性CT反馈如何动态地相互作用以调节丘脑-皮层视觉处理的基本问题。

In textbooks, the visual system is often portrayed consisting of processing stages that are arranged in a hierarchy and connected via feedforward projections. Considering the anatomy of the visual system in more detail, however, it becomes clear that feedforward projections are often grossly outnumbered by their feedback counterparts. This general rule also applies to the dorsolateral geniculate nucleus (dLGN) of the thalamus, where ~30% of synaptic inputs to relay cells are made by corticothalamic (CT) pyramidal cells, while only ~10% constitute feedforward inputs from retinal ganglion cells. How this anatomically massive feedback projection to one of the earliest visual processing stages influences representations in dLGN and impacts computations in the thalamocortical loop has so far remained incompletely understood.The proposed research is a follow-up project that continues to be centered around the impact of corticothalamic feedback on information processing in the early visual system. While our research in the previous funding period provided insights into the retinotopic organization of CT feedback circuits in thalamus and the dual nature of CT feedback effects in shaping spatial processing, i.e. facilitation and suppression, our central aim for this follow-up proposal is to elucidate the spatio-temporal dynamics of feedforward and feedback processing in thalamo-cortico-thalamic interactions. In particular, we will (1) isolate the temporal impact of CT feedback in dLGN and visTRN, we will (2) investigate the role of CT feedback in shaping spatio-temporal selectivity by using pathway-specific, optogenetic suppression of CT feedback terminals and simultaneous recordings from thalamus and cortex, and we will (3) probe the role of CT feedback in thalamocortical rhythms and communication.Together, this research promises to contribute to answering the fundamental question of how the direct excitatory and indirect inhibitory CT feedback dynamically interact to modulate thalamo-cortical visual processing.