Wetmore Daniel Z, Baker Stuart N
Neuroscience Graduate Program, Stanford University School of Medicine, Stanford, CA 94305, USA.
J Physiol. 2004 Mar 16;555(Pt 3):831-50. doi: 10.1113/jphysiol.2003.048918. Epub 2004 Jan 14.
A recently developed method permits calculation of the post-spike distance-to-threshold trajectory from an extracellularly recorded spontaneous spike train, using a transform of the interspike interval histogram. We applied this method to 61 single neurones recorded from the primary motor cortex of an awake behaving monkey; 39 cells were antidromically identified as pyramidal tract neurones (PTNs). The cells fell into three categories. Fifty-three trajectories (37 from PTNs) had statistically significant peaks 10-60 ms after the preceding spike. Six neurones (2 PTNs) had non-peaked trajectories which rose exponentially towards threshold. Two cells (both unidentified) had trajectories which declined monotonically away from threshold with increasing post-spike latency. The peaked trajectories were unlikely simply to be an artefact of changing firing rate, which potentially can invalidate this method. Firstly, computer simulations confirmed that the method could accurately re-create both exponential and peaked trajectories, even in the presence of the same rate modulation as seen experimentally. Secondly, the responses of eight cells to weak single pulse intracortical microstimulation (20 microA) through a nearby electrode were measured. For each cell, including representatives of all three trajectory shapes, the modulation of response probability with post-spike latency was consistent with the trajectory computed from the spontaneous discharge. We also demonstrated that cells showed a peaked trajectory during periods with either high or low spontaneous network oscillations, so that the peaks were likely to be generated in part by single cell properties rather than exclusively by network activity. We conclude that many single neurones in motor cortex have an increased probability of firing a spike around 30 ms after the previous action potential. This could act to enhance synchronized oscillatory discharge among populations of cells at functionally relevant frequencies.
最近开发的一种方法允许通过对峰间期直方图进行变换，从细胞外记录的自发尖峰序列计算出峰后距离阈值轨迹。我们将此方法应用于从一只清醒行为猴的初级运动皮层记录的61个单个神经元；其中39个细胞经逆向鉴定为锥体束神经元（PTNs）。这些细胞分为三类。53条轨迹（37条来自PTNs）在前一个尖峰后10 - 60毫秒有统计学上显著的峰值。6个神经元（2个PTNs）有非峰值轨迹，其向阈值呈指数上升。2个细胞（均未鉴定）的轨迹随着峰后潜伏期增加而单调地远离阈值下降。这些峰值轨迹不太可能仅仅是 firing rate 变化的假象，而这可能会使该方法无效。首先，计算机模拟证实，即使存在与实验中所见相同的速率调制，该方法也能准确地重新创建指数和峰值轨迹。其次，测量了8个细胞通过附近电极对弱单脉冲皮层内微刺激（20微安）的反应。对于每个细胞，包括所有三种轨迹形状的代表，反应概率随峰后潜伏期的调制与从自发放电计算出的轨迹一致。我们还证明，细胞在自发网络振荡高或低的时期都表现出峰值轨迹，因此这些峰值可能部分是由单细胞特性产生的，而不是完全由网络活动产生的。我们得出结论，运动皮层中的许多单个神经元在前一个动作电位后约30毫秒左右发放尖峰的概率增加。这可能有助于增强功能相关频率下细胞群体之间的同步振荡放电。
