Integrative properties of visual cortex neurons

我们的长期目标是了解视觉皮质的信息处理。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，我们将集中于视觉激活感受野(RF)内外区域所产生的输入的整合。周围刺激(RF外)以对比度和方位依赖的方式促进或抑制视皮层神经元对RF内刺激的反应。已有研究表明，这种调制效应依赖于规则峰(RS)和快峰(FS)细胞对刺激反应的不对称性，这两种细胞分别是主要的兴奋性和抑制性神经元皮质类型。众所周知，FS细胞在体外表现出对电流注入的反应，其放电频率比RS细胞更急剧地增加，并达到更高和更持久的值。此外，人们对不同类型的新皮质电生理细胞的视觉特性知之甚少。我们将使用麻醉动物体内的细胞内记录，与标准的和更具创新性的视觉刺激范例相一致。我们将沿着以下目标进行：(I)建立视觉皮质电生理和功能细胞特性之间的对应关系；(Ii)展示RS和FS细胞对电流注射和刺激对比的反应的不对称性；以及(Iii)证明由于对比而引起的环境效应的变化是基于突触输入的平衡从兴奋性转向抑制性的。据预测，这种转变只会发生在RS细胞中，而FS细胞将表现出进一步的促进作用，相反地，增加。这一预测与我们的初步数据和体外研究显示IPSP只对更高强度的远程皮质连接刺激有反应是完全一致的。为了刻画周围刺激调制作用下的突触事件，我们建议使用具有不同对比度和方向的闪光条。这些条将在RF外部的不同位置闪现，并且相对于在RF内闪现的条在不同时间闪现。这一实验方法还将使我们能够研究环绕刺激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.