Menon V, Freeman W J, Cutillo B A, Desmond J E, Ward M F, Bressler S L, Laxer K D, Barbaro N, Gevins A S
EEG Systems Laboratory, San Francisco, CA 94105, USA.
Electroencephalogr Clin Neurophysiol. 1996 Feb;98(2):89-102. doi: 10.1016/0013-4694(95)00206-5.
Animal electrocorticogram (ECoG) studies have shown that spatial patterns in the gamma band (>20 Hz) reflect perceptual categorization. Spatio-temporal correlations were investigated in the 20-50 Hz range in search for similar phenomena in human ECoG. ECoGs were recorded in a somatosensory discrimination task from 64-electrode subdural grid arrays, with inter-electrode spacing of 1 cm, overlying somatosensory, motor and superior temporal cortices in 2 patients with intractable epilepsy. Bootstrap techniques were devised to analyze the spatial and temporal characteristics of the correlations. Despite an extensive search, no evidence was found for globally correlated activity related to behavior either in narrow (1.e., 35-45 Hz) or broad (i.e., 20-50 Hz) bands. Spatial patterns, extracted using principal component analysis, could not be classified with respect to stimulus type in any time interval. Instead, spatially and temporally intermittent synchronization was observed between pairs of electrodes in 1 cm X 1 cm regions with high variability within and across trials. The distribution of correlation coefficients differed substantially from background levels at inter-electrode distances of 1 cm and 1.4 cm but not 2 cm or more. The minimum duration of correlation, the decorrelation time, of the ECoG was about 50 msec; the average correlation duration at 1 cm inter-electrode distance was about 150 msec; and the recurrence rate of significant correlation peaks was about 1.3/sec. The findings suggest that the surface diameters of domains of spatially correlated activity underlying perceptual categorization in human gamma band ECoG are limited to less than 2 cm and that the intermittent synchronization observed across separations of 1 cm and 1.4 cm is not solely due to volume conduction. Thus, if such gamma band spatial patterns exist in the human brain, no existing technology would be capable of measuring them at the scalp, and subdural electrode arrays for cortical surface recording would have to have spacings under 5 mm.
动物脑电皮质图（ECoG）研究表明，伽马波段（>20赫兹）的空间模式反映了感知分类。研究人员在20 - 50赫兹范围内研究了时空相关性，以探寻人类ECoG中是否存在类似现象。在两项针对难治性癫痫患者的研究中，通过64电极硬膜下网格阵列记录ECoG，电极间距为1厘米，覆盖躯体感觉、运动和颞上皮质，同时患者需完成体感辨别任务。研究人员设计了自展技术来分析相关性的时空特征。尽管进行了广泛搜索，但在窄波段（即35 - 45赫兹）或宽波段（即20 - 50赫兹）中均未发现与行为相关的全局相关活动的证据。使用主成分分析提取的空间模式在任何时间间隔内都无法根据刺激类型进行分类。相反，在1厘米×1厘米区域内的电极对之间观察到了空间和时间上的间歇性同步，且试验内和试验间的变异性都很高。相关系数的分布在电极间距为1厘米和1.4厘米时与背景水平有显著差异，但在2厘米及以上时则无差异。ECoG相关性的最短持续时间，即去相关时间约为50毫秒；电极间距为1厘米时的平均相关持续时间约为150毫秒；显著相关峰值的重现率约为1.3次/秒。研究结果表明，人类伽马波段ECoG中感知分类背后的空间相关活动区域的表面直径限制在小于2厘米，并且在1厘米和1.4厘米间距处观察到的间歇性同步并非仅由容积传导引起。因此，如果人类大脑中存在此类伽马波段空间模式，现有的任何技术都无法在头皮上测量它们，而用于皮质表面记录的硬膜下电极阵列的间距必须小于5毫米。
