Integrative properties of visual cortex neurons

我们的长期目标是了解视觉皮层的信息处理过程。皮层处理的一个基本方面是通过单个细胞和局部网络整合来自不同来源的输入。在这里，我们将集中讨论由感受野内外区域的视觉激活所产生的输入的整合。周围刺激（RF外）促进或抑制视觉皮层神经元对RF内刺激的反应，以对比和方向依赖的方式。有人提出，这种调节作用取决于规则尖峰（RS）和快速尖峰（FS）细胞对刺激对比反应的不对称性，这两种细胞分别是主要的兴奋性和抑制性神经元皮层类型。众所周知，体外培养的FS细胞对电流注射的反应率比RS细胞增加得更快，达到更高和更持久的值。此外，人们对新皮层不同电生理细胞类别的视觉特性知之甚少。我们将在麻醉动物体内使用细胞内记录，以配合标准和更创新的视觉刺激范例。我们将沿着以下目标继续进行：(i)建立视觉皮层中电生理和功能细胞特性之间的对应关系，（ii）证明RS和FS细胞对电流注射和刺激对比的反应不对称，以及（iii）证明由于对比引起的环绕效应的变化是基于突触输入平衡从兴奋性到抑制性的转变。预测这种转变只会发生在RS细胞中，而FS细胞则会随着对比度的增加而进一步促进。这一预测与我们的初步数据和体外研究完全一致，体外研究显示ipsp仅对长距离皮质连接的高强度刺激有反应。为了描述周围刺激调节作用下的突触事件，我们建议使用不同对比度和方向的闪光条。这些条将在射频外的不同位置和不同时间闪烁，相对于射频内闪烁的条。这种实验方法也将使我们能够研究周围刺激的调节效应的时空特性。

Our long term goal is to understand information processing in visual cortex. A fundamental aspect of cortical processing is the integration of inputs from different sources by single cells and local networks. Here we will focus on the integration of inputs arising from visual activation of areas inside and outside the receptive field (RF). Surround stimuli (outside the RF) facilitate or suppress the responses of visual cortex neurons to stimuli inside their RF in a contrast and orientation dependent manner. It has been proposed that such modulatory effects depend on asymmetries in the response to stimulus contrast between regular spiking (RS) and fast spiking (FS) cells, which are the main excitatory and inhibitory neuronal cortical types, respectively. It is known that FS cells in vitro show firing rates in response to current injection that increase more steeply and reach higher and more sustained values than RS cells. In addition, little is known about the visual properties of the different electrophysiological cell classes of the neocortex. We will use intracellular recordings in vivo in anesthetized animals in concert with both standard and more innovative paradigms of visual stimulation. We will proceed along the following aims: (i) Establish the correspondence between electrophysiological and functional cell properties in the visual cortex, (ii) demonstrate asymmetries in the response to current injection and stimulus contrast between RS and FS cells, and (iii) demonstrate that the changes in surround effects due to contrast are based on a shift on the balance of synaptic inputs from excitatory to inhibitory. The prediction is that this shift will occur only in RS cells, while FS cells will show further facilitation with increases in contrast. This prediction is in complete agreement with our preliminary data and with in vitro studies showing IPSPs in response only to higher intensities of stimulation of the long range cortical connections. In order to characterize the synaptic events that underlie the modulatory actions of surround stimuli, we propose to use flashed bars with different contrasts and orientations. These bars will be flashed at different locations outside the RF and at different times with respect to the bars flashed inside the RF. This experimental approach will also allow us to study the spatiotemporal properties of the modulatory effects of surround stimuli.