Baker S N, Spinks R, Jackson A, Lemon R N
Sobell Department of Neurophysiology, Institute of Neurology, London WC1N 3BG, United Kingdom.
J Neurophysiol. 2001 Feb;85(2):869-85. doi: 10.1152/jn.2001.85.2.869.
Neural synchronization in the cortex, and its potential role in information coding, has attracted much recent attention. In this study, we have recorded long spike trains (mean, 33,000 spikes) simultaneously from multiple single neurons in the primary motor cortex (M1) of two conscious macaque monkeys performing a precision grip task. The task required the monkey to use its index finger and thumb to move two spring-loaded levers into a target, hold them there for 1 s, and release for a food reward. Synchrony was analyzed using a time-resolved cross-correlation method, normalized using an estimate of the instantaneous firing rate of the cell. This was shown to be more reliable than methods using trial-averaged firing rate. A total of 375 neurons was recorded from the M1 hand area; 235 were identified as pyramidal tract neurons. Synchrony was weak [mean k' = 1.05 +/- 0.04 (SD)] but widespread among pairs of M1 neurons (218/1359 pairs with above-chance synchrony), including output neurons. Synchrony usually took the form of a broad central peak [average width, 18.7 +/- 8.7 (SD) ms]. There were marked changes during different phases of the task. As a population, synchrony was greatest during the steady hold period in striking contrast to the averaged cell firing rate, which was maximal when the animal was moving the levers into target. However, the modulation of synchrony during task performance showed considerable variation across individual cell pairs. Two types of synchrony were identified: oscillatory (with periodic side lobes in the cross-correlation) and nonoscillatory. Their relative contributions were quantified by filtering the cross-correlations to exclude either frequencies from 18 to 37 Hz or all higher and lower frequencies. At the peak of population synchrony during the hold period, about half (51.7% in one monkey, 56.2% in the other) of the synchronization was within this oscillatory bandwidth. This study provides strong support for assemblies of neurons being synchronized during specific phases of a complex task with potentially important consequences for both information processing within M1 and for the impact of M1 commands on target motoneurons.
皮层中的神经同步及其在信息编码中的潜在作用，近来备受关注。在本研究中，我们记录了两只清醒猕猴在执行精确抓握任务时，从其初级运动皮层（M1）的多个单个神经元同时记录到的长脉冲序列（平均33,000个脉冲）。该任务要求猴子用食指和拇指将两个弹簧加载的杠杆移至目标位置，在那里保持1秒，然后松开以获取食物奖励。使用时间分辨互相关方法分析同步性，并使用细胞瞬时放电率的估计值进行归一化。结果表明，这比使用试验平均放电率的方法更可靠。从M1手部区域共记录了375个神经元；其中235个被鉴定为锥体束神经元。同步性较弱[平均k' = 1.05 +/- 0.04（标准差）]，但在M1神经元对中广泛存在（218/1359对具有高于机遇水平的同步性），包括输出神经元。同步性通常表现为一个宽阔的中心峰值[平均宽度，18.7 +/- 8.7（标准差）毫秒]。在任务的不同阶段有明显变化。总体而言，在稳定握持期同步性最强，这与平均细胞放电率形成鲜明对比，平均细胞放电率在动物将杠杆移向目标时最高。然而，任务执行过程中同步性的调制在各个细胞对之间表现出相当大的差异。识别出两种同步类型：振荡性（互相关中有周期性旁瓣）和非振荡性。通过对互相关进行滤波以排除18至37赫兹的频率或所有更高和更低频率，对它们的相对贡献进行了量化。在握持期群体同步性的峰值时，约一半（一只猴子为51.7%，另一只猴子为56.2%）的同步性处于该振荡带宽内。本研究为神经元在复杂任务的特定阶段同步集合提供了有力支持，这对M1内的信息处理以及M1指令对目标运动神经元的影响可能具有重要意义。
