Agmon Ariel
Department of Neurobiology and Anatomy and the Sensory Neuroscience Research Center, West Virginia University, Morgantown, WV, 26506-9303, USA.
Neural Syst Circuits. 2012 May 2;2(1):5. doi: 10.1186/2042-1001-2-5.
Precise spike synchrony, at the millisecond or even sub-millisecond time scale, has been reported in different brain areas, but its neurobiological meaning and its underlying mechanisms remain unknown or controversial. Studying these questions is complicated by the lack of a validated, well-normalized and robust index for quantifying synchrony. Previously used measures of synchrony are often improperly normalized and thereby are not comparable between different experimental conditions, are sensitive to variations in firing rate or to the firing rate differential between the two neurons, and/or rely on untenable assumptions of firing rate stationarity and Poisson statistics. I describe here a novel measure, the Jitter-Based Synchrony Index (JBSI), that overcomes these issues.
The JBSI method is based on the introduction of virtual spike jitter. While previous implementations of the jitter method used it only to detect synchrony, the JBSI method also quantifies synchrony. Previous implementations of the jitter method used computationally intensive Monte Carlo simulations to generate surrogate spike trains, whereas the JBSI is computed analytically. The JBSI method does not assume any specific firing model, and does not require that the spike trains be locked to a repeating external stimulus. The JBSI can assume values from 1 (maximal possible synchrony) to -1 (minimal possible synchrony) and is therefore properly normalized. Using simulated Poisson spike trains with introduced controlled spike coincidences, I demonstrate that the JBSI is a linear measure of the spike coincidence rate, is independent of the mean firing frequency or the firing frequency differential between the two neurons, and is not sensitive to co-modulations in the firing rates of the two neurons. In contrast, several commonly used synchrony indices fail under one or more of these scenarios. I also demonstrate how the JBSI can be used to estimate the spike timing precision in the system.
The JBSI is a conceptually simple and computationally efficient method that can be used to compute the statistical significance of firing synchrony, to quantify synchrony as a well-normalized index, and to estimate the degree of temporal precision in the system.
在不同脑区已报道存在精确至毫秒甚至亚毫秒时间尺度的尖峰同步，但它的神经生物学意义及其潜在机制仍不明确或存在争议。由于缺乏一个经过验证、良好归一化且稳健的同步量化指标，对这些问题的研究变得复杂。先前使用的同步测量方法往往归一化不当，因此在不同实验条件下不可比，对放电率变化或两个神经元之间的放电率差异敏感，和/或依赖于放电率平稳性和泊松统计的不合理假设。我在此描述一种新的测量方法，即基于抖动的同步指数（JBSI），它克服了这些问题。
JBSI方法基于虚拟尖峰抖动的引入。虽然抖动方法的先前实现仅将其用于检测同步，但JBSI方法还对同步进行量化。抖动方法的先前实现使用计算密集型的蒙特卡罗模拟来生成替代尖峰序列，而JBSI是通过解析计算得出的。JBSI方法不假设任何特定的放电模型，也不要求尖峰序列锁定到重复的外部刺激。JBSI可以取从1（最大可能同步）到 -1（最小可能同步）的值，因此经过了适当的归一化。使用引入了受控尖峰重合的模拟泊松尖峰序列，我证明JBSI是尖峰重合率的线性测量指标，与两个神经元的平均放电频率或放电频率差异无关，并且对两个神经元放电率的共同调制不敏感。相比之下，几种常用的同步指数在这些情况中的一种或多种情况下会失效。我还展示了JBSI如何用于估计系统中的尖峰时间精度。
JBSI是一种概念上简单且计算高效的方法，可用于计算放电同步的统计显著性，将同步量化为一个良好归一化的指标，并估计系统中的时间精度程度。
