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。 皮层处理的一个基本方面是通过单细胞和局部网络整合来自不同来源的输入。 在这里，我们将重点放在整合的输入所产生的视觉激活的区域内和外的感受野（RF）。 周围刺激（RF外）促进或抑制视觉皮层神经元的反应，以对比度和方向依赖的方式在其RF内的刺激。 有人提出，这种调节作用依赖于不对称的反应，刺激之间的对比度定期尖峰（RS）和快速尖峰（FS）细胞，这是主要的兴奋性和抑制性神经元皮层类型，分别。 已知FS细胞在体外显示出响应于电流注入的放电率，其比RS细胞增加得更陡并达到更高和更持续的值。 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，与标准和更创新的视觉刺激范例相一致。 我们将继续沿着以下目标：（一）建立在视觉皮层的电生理和功能细胞特性之间的对应关系，（二）演示RS和FS细胞之间的电流注入和刺激对比度的反应的不对称性，以及（三）演示由于对比度的变化，在周围的影响是基于从兴奋性到抑制性的突触输入的平衡的转变。 预测是，这种移位将仅发生在RS细胞中，而FS细胞将随着对比度的增加而显示出进一步的促进作用。 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IPSPs仅对长距离皮层连接的较高强度刺激作出反应。 为了表征周围刺激的调制作用的基础上的突触事件，我们建议使用不同的对比度和方向的闪光条。这些条将在RF外部的不同位置和相对于RF内部闪速的条的不同时间闪速。 这种实验方法也将使我们能够研究周围刺激的调制效应的时空特性。

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.