Freeman W J, van Dijk B W
Department of Physiology-Anatomy, University of California, Berkeley 94720.
Brain Res. 1987 Oct 6;422(2):267-76. doi: 10.1016/0006-8993(87)90933-4.
A preliminary assay was made of the existence of time-space coherence patterns of fast EEG activity in the visual cortex of a Rhesus monkey. The primary intent of the present study was to evaluate the similarities and differences in relation to the olfactory bulb, where such coherences have been described and have been demonstrated to be associated with behaviour. Segments 1.5 s in duration were recorded simultaneously without averaging from 16 to 35 subdural electrodes fixed over the left occipital lobe in an array 3.6 cm X 2.8 cm. Each segment was taken during the delivery of a visual conditioned stimulus (CS) and the performance of a conditioned response (CR) by a well-trained Rhesus monkey. The EEGs appeared chaotic with irregular bursts lasting 75-200 ms, resembling those in the olfactory EEG but with lower peak frequencies. Fourier spectra showed broad distributions of power resembling '1/f noise' with multiple peaks in the range of 20-40 Hz. Time intervals were selected where coherent activity seemed to be present at a number of electrodes. A dominant component waveform that was common to all channels was extracted by principal components analysis (PCA) of each segment. The distribution of the power of this component across the electrodes (the factor loadings) was used to describe the spatial pattern of the coherent cortical activity. Statistical analyses suggested that different patterns could be associated to the CS and the CR, as has been found in the olfactory system. These patterns remained stable over a 6 week recording interval. The patterns can be better discriminated, when the factor loadings of each channel are normalized to zero mean and unit variance, to discard a basic pattern of power distribution, which may reflect anatomical and electrode positioning factors that are related to behavioral information processing by the cortex. The wide spatial distribution of the common patterns found suggests that EEG patterns that manifest differing states of the visual cortex may also be accessible with scalp electrodes.
对恒河猴视觉皮层中快速脑电图活动的时空相干模式的存在进行了初步测定。本研究的主要目的是评估与嗅球相关的异同，在嗅球中已经描述了这种相干性并证明其与行为有关。在一个3.6厘米×2.8厘米的阵列中，从固定在左枕叶上的16至35个硬膜下电极同时记录持续1.5秒的片段，不进行平均。每个片段是在一只训练有素的恒河猴进行视觉条件刺激（CS）和条件反应（CR）时采集的。脑电图看起来很混乱，有持续75 - 200毫秒的不规则爆发，类似于嗅觉脑电图，但峰值频率较低。傅里叶频谱显示功率分布广泛，类似于“1/f噪声”，在20 - 40赫兹范围内有多个峰值。选择了一些电极似乎存在相干活动的时间间隔。通过对每个片段进行主成分分析（PCA），提取了所有通道共有的主导成分波形。该成分在电极上的功率分布（因子载荷）用于描述相干皮层活动的空间模式。统计分析表明，不同的模式可能与CS和CR相关，这与嗅觉系统中发现的情况相同。这些模式在6周的记录间隔内保持稳定。当将每个通道的因子载荷归一化为零均值和单位方差时，可以更好地区分这些模式，以舍弃功率分布的基本模式，该模式可能反映与皮层行为信息处理相关的解剖和电极定位因素。所发现的共同模式的广泛空间分布表明，通过头皮电极也可以获取显示视觉皮层不同状态的脑电图模式。
