QUANTITATIVE STUDIES OF CORTICAL VISUAL PROCESSING

本研究的目的是揭示灵长类初级视皮层(V1区)产生新反应的神经回路。这些实验旨在揭示皮质动力学、抑制信号、感受野非线性和皮层内功能性连接在产生对视觉刺激属性(方向、运动方向、空间频率、长度和宽度)的神经反应选择性中所起的作用。调谐动态：我们将使用反向相关技术测量不同V1层中调谐选择性的动态变化。最近对这种方法的一项改进(包括“空白”图像)提供了确定兴奋和抑制的动力学，并确定它们对细胞反应的贡献的方法。使用这种方法，我们将表征调谐到方向、运动方向、空间频率、长度和宽度的动力学。从响应的一开始就存在明显的调谐选择性的假设将得到检验。抑制的作用：我们将检验这一假设，即抑制信号参与塑造神经反应的调谐选择性。为了便于检测细胞外记录中的抑制信号，我们将在条件刺激(二维噪声)的基础上测量调谐曲线，其目的是将皮质的活动提高到通常较低的自发频率以上。我们将寻找抑制的证据：在调谐曲线上，反应被压低到基线活动以下的区域。时空线性：我们将测试这样的假设，即简单的细胞表现为一个线性时空过滤器，然后是一个静态的非线性。我们将检验这一假设，即简单的方法避免了与输出非线性对响应的贡献相关的问题。本实验的一个目的是确定准线性机制是否足以解释简单电池的调谐特性。功能连通性：我们将开始探索大脑皮质相互作用在空间、方向和空间频率维度上的模式。为了实现这一目标，我们将同时记录成对的神经元，当它们的反应通过使用条件刺激而提高时。这些实验旨在从多个概念角度研究产生皮质选择性的神经机制。综上所述，这些发现将促进我们对V1处理丘脑输入的计算和策略的理解。

Our objective in this research is to reveal the neural circuitry generating novel response properties in the primate primary visual cortex (area V1). The experiments are designed to uncover the role cortical dynamics, suppressive signals, receptive field non-linearities, and functional intra- cortical connectivity play in the generation of neural response selectivity to visual stimulus attributes: orientation, direction of motion, spatial frequency, length, and width. Dynamics of Tuning: We will measure the dynamics of tuning selectivity in the different V1 layers using reverse correlation techniques. A recent improvement to this method (the inclusion of "blank" images) provides the means to determine the dynamics of excitation and inhibition, and to establish their contribution to the cell's response. Using this methodology, we will characterize the dynamics of tuning to orientation, direction of motion, spatial frequency, length, and width. The hypothesis that sharp tuning selectivity is present from the very beginning of the response will be tested. Role of Suppression: We will test the hypothesis that suppressive signals are involved in shaping the tuning selectivity of neural responses. To facilitate the detection of suppressive signals in extracellular recordings, we will measure tuning curves on top of a conditioning stimulus (two-dimensional noise) whose purpose is to elevate the activity of the cortex above the usually low spontaneous rates. We will seek evidence of inhibition: regions in the tuning curve where responses are depressed below the baseline activity. Spatio-temporal Linearity: We will test the hypothesis that simple cells behave as a linear spatio-temporal filter followed by a static non-Linearity. We will test the hypothesis that simple method that avoids the problems associated with the contribution of the output non-Linearity to the response. A goal of this experiment is to determine if quasi-linear mechanisms are sufficient to account for the tuning properties of simple cells. Functional connectivity: We will begin to explore the pattern of cortical interactions in the dimensions of space, orientation and spatial frequency. To achieve this goal, we will record simultaneously from pairs of neurons when their responses are elevated by the use of a conditioning stimulus. These experiments are designed to study, from multiple conceptual angles, the neural mechanisms generating cortical selectivity.. Taken together, these findings will advance our understanding of the computations and strategies used by V1 to process thalamic input.