Olufsen Mette S, Whittington Miles A, Camperi Marcelo, Kopell Nancy
Department of Mathematics, North Carolina State University, Raleigh, NC 27659-8205, USA.
J Comput Neurosci. 2003 Jan-Feb;14(1):33-54. doi: 10.1023/a:1021124317706.
Gamma (30-80 Hz) and beta (12-30 Hz) oscillations such as those displayed by in vitro hippocampal (CA1) slice preparations and by in vivo neocortical EEGs often occur successively, with a spontaneous transition between them. In the gamma rhythm, pyramidal cells fire together with the interneurons, while in the beta rhythm, pyramidal cells fire on a subset of cycles of the interneurons. It is shown that gamma and beta rhythms have different properties with respect to creation of cell assemblies. In the presence of heterogeneous inputs to the pyramidal cells, the gamma rhythm creates an assembly of firing pyramidal cells from cells whose drive exceeds a threshold. During the gamma to beta transition, a slow outward potassium current is activated, and as a result the cell assembly vanishes. The slow currents make each of the pyramidal cells fire with a beta rhythm, but the field potential of the network still displays a gamma rhythm. Hebbian changes of connections among the pyramidal cells give rise to a beta rhythm, and the cell assemblies are recovered with a temporal separation between cells firing in different cycles. We present experimental evidence showing that such a separation can occur in hippocampal slices.
伽马（30 - 80赫兹）和贝塔（12 - 30赫兹）振荡，例如体外海马体（CA1）切片标本以及体内新皮质脑电图所显示的振荡，常常相继出现，且它们之间会自发转换。在伽马节律中，锥体细胞与中间神经元同步放电，而在贝塔节律中，锥体细胞在中间神经元的部分放电周期中放电。研究表明，伽马和贝塔节律在细胞集群的形成方面具有不同特性。在锥体细胞存在异质性输入的情况下，伽马节律会从驱动超过阈值的细胞中创建一个放电锥体细胞集群。在伽马向贝塔转换期间，一个缓慢的外向钾电流被激活，结果细胞集群消失。缓慢的电流使每个锥体细胞以贝塔节律放电，但网络的场电位仍显示为伽马节律。锥体细胞之间连接的赫布变化产生了贝塔节律，并且细胞集群在不同周期放电的细胞之间出现时间间隔后得以恢复。我们提供了实验证据表明这种间隔可以在海马体切片中出现。
