Instituto de Biofísica Carlos Chagas Filho, Universidade Federal Do Rio de Janeiro, 21941-900, Rio de Janeiro, RJ, Brasil.
Programa de Pós-Graduação Em Ciências Cirúrgicas, Faculdade de Medicina, UFRJ, Rio de Janeiro, RJ, Brasil.
Brain Struct Funct. 2021 Dec;226(9):2881-2895. doi: 10.1007/s00429-021-02311-x. Epub 2021 Jun 4.
A general assumption in visual neuroscience is that basic receptive field properties such as orientation and direction selectivity are constructed within intrinsic neuronal circuits and feedforward projections. In addition, it is assumed that general neuronal excitability and responsiveness in early visual areas is to a great extent independent of feedback input originating in areas higher in the stream. Here, we review the contribution of feedback projections from MT, V4 and pulvinar to the receptive field properties of V2 neurons in the anesthetized and paralyzed monkey. Importantly, our results contradict both of these assumptions. We separately inactivated each of these three brain regions using GABA pressure injections, while simultaneously recording V2 single unit activity before and hours after inactivation. Recordings and GABA injections were carried out in topographically corresponding regions of the visual field. We outline the changes in V2 activity, responsiveness and receptive field properties for early, mid and late post-injection phases. Immediately after injection, V2 activity is globally suppressed. Subsequently, there is an increase in stimulus-driven relative to spontaneous neuronal activity, which improves the signal-to-noise coding for the oriented moving bars. Notably, V2 tuning properties change substantially relative to its pre-injection selectivity profile. The resulting increase or decrease in selectivity could not be readily predicted based on the selectivity profile of the inactivated site. Finally, V2 activity rebounds before returning to it pre-injection profile Our results show that feedback projections profoundly impact neuronal circuits in early visual areas, and may have been heretofore largely underestimated in their physiological role.
在视觉神经科学中，一个普遍的假设是，诸如方向和方向选择性等基本感受野特性是在内在神经元回路和前馈投射中构建的。此外，人们还假设，早期视觉区域中的一般神经元兴奋性和反应性在很大程度上独立于起源于流中较高区域的反馈输入。在这里，我们回顾了来自 MT、V4 和丘脑枕的反馈投射对麻醉和麻痹猴子 V2 神经元感受野特性的贡献。重要的是，我们的结果与这两个假设都相矛盾。我们使用 GABA 压力注射分别使这三个脑区失活，同时在失活前后的几个小时内记录 V2 单个单元的活动。记录和 GABA 注射是在视觉场的拓扑对应区域进行的。我们概述了早期、中期和后期注射阶段 V2 活动、反应性和感受野特性的变化。注射后立即，V2 活动被全局抑制。随后，刺激驱动的神经元活动相对于自发神经元活动增加，这改善了定向运动棒的信号噪声编码。值得注意的是，V2 调谐特性相对于其预注射选择性轮廓发生了实质性变化。相对于失活部位的选择性轮廓，这种选择性的增加或减少不能轻易预测。最后，V2 活动在恢复到预注射状态之前反弹。我们的结果表明，反馈投射深刻地影响了早期视觉区域的神经元回路，并且在其生理作用方面可能迄今为止被大大低估了。
