Hu Hang, Agmon Ariel
Department of Neurobiology and Anatomy and the Sensory Neuroscience Research Center, West Virginia University, Morgantown, West Virginia.
Department of Neurobiology and Anatomy and the Sensory Neuroscience Research Center, West Virginia University, Morgantown, West Virginia
J Neurophysiol. 2015 Jul;114(1):624-37. doi: 10.1152/jn.00304.2015. Epub 2015 May 13.
Precise spike synchrony has been widely reported in the central nervous system, but its functional role in encoding, processing, and transmitting information is yet unresolved. Of particular interest is firing synchrony between inhibitory cortical interneurons, thought to drive various cortical rhythms such as gamma oscillations, the hallmark of cognitive states. Precise synchrony can arise between two interneurons connected electrically, through gap junctions, chemically, through fast inhibitory synapses, or dually, through both types of connections, but the properties of synchrony generated by these different modes of connectivity have never been compared in the same data set. In the present study we recorded in vitro from 152 homotypic pairs of two major subtypes of mouse neocortical interneurons: parvalbumin-containing, fast-spiking (FS) interneurons and somatostatin-containing (SOM) interneurons. We tested firing synchrony when the two neurons were driven to fire by long, depolarizing current steps and used a novel synchrony index to quantify the strength of synchrony, its temporal precision, and its dependence on firing rate. We found that SOM-SOM synchrony, driven solely by electrical coupling, was less precise than FS-FS synchrony, driven by inhibitory or dual coupling. Unlike SOM-SOM synchrony, FS-FS synchrony was strongly firing rate dependent and was not evident at the prototypical 40-Hz gamma frequency. Computer simulations reproduced these differences in synchrony without assuming any differences in intrinsic properties, suggesting that the mode of coupling is more important than the interneuron subtype. Our results provide novel insights into the mechanisms and properties of interneuron synchrony and point out important caveats in current models of cortical oscillations.
精确的峰电位同步在中枢神经系统中已有广泛报道，但其在信息编码、处理和传递中的功能作用尚未明确。特别令人感兴趣的是抑制性皮层中间神经元之间的放电同步，这种同步被认为驱动各种皮层节律，如γ振荡，而γ振荡是认知状态的标志。精确同步可出现在通过缝隙连接进行电连接、通过快速抑制性突触进行化学连接或通过两种连接方式同时存在的两个中间神经元之间，但在同一数据集中从未对这些不同连接模式产生的同步特性进行过比较。在本研究中，我们在体外记录了152对小鼠新皮层两种主要亚型的同型中间神经元：含小白蛋白的快速放电（FS）中间神经元和含生长抑素的（SOM）中间神经元。当通过长时去极化电流阶跃驱动这两个神经元放电时，我们测试了放电同步性，并使用一种新的同步指数来量化同步强度、其时间精度及其对放电频率的依赖性。我们发现，仅由电耦合驱动的SOM - SOM同步比由抑制性或双重耦合驱动的FS - FS同步精度更低。与SOM - SOM同步不同，FS - FS同步强烈依赖于放电频率，并且在典型的40Hzγ频率下不明显。计算机模拟再现了这些同步差异，而无需假设内在特性存在任何差异，这表明耦合模式比中间神经元亚型更重要。我们的结果为中间神经元同步的机制和特性提供了新的见解，并指出了当前皮层振荡模型中的重要注意事项。
