INSERM, U751, Laboratoire de Neurophysiologie et Neuropsychologie, Marseille, France.
Clin Neurophysiol. 2010 Mar;121(3):301-10. doi: 10.1016/j.clinph.2009.10.019. Epub 2009 Dec 1.
To analyze interictal High frequency oscillations (HFOs) as observed in the medial temporal lobe of epileptic patients and animals (ripples, 80-200Hz and fast ripples, 250-600Hz). To show that the identification of interictal HFOs raises some methodological issues, as the filtering of sharp transients (e.g., epileptic spikes or artefacts) or signals with harmonics can result in "false" ripples. To illustrate and quantify the occurrence of false ripples on filtered EEG traces.
We have performed high-pass filtering on both simulated and real data. We have also used two alternate methods: time-frequency analysis and matching pursuit.
Two types of events were shown to produce oscillations after filtering that could be confounded with actual oscillatory activity: sharp transients and harmonics of non-sinusoidal signals.
High-pass filtering of EEG traces for detection of oscillatory activity should be performed with great care. Filtered traces should be compared to original traces for verification of presence of transients. Additional techniques such as time-frequency transforms or sparse decompositions are highly beneficial.
Our study draws the attention on an issue of great importance in the marking of HFOs on EEG traces. We illustrate complementary methods that can help both researchers and clinicians.
分析癫痫患者和动物内侧颞叶的发作间期高频振荡（HFOs）（棘波，80-200Hz 和快棘波，250-600Hz）。表明发作间期 HFOs 的识别存在一些方法学问题，因为尖锐瞬变（例如癫痫棘波或伪迹）或具有谐波的信号的滤波可能导致“假”棘波。说明并量化滤波后 EEG 迹线上假棘波的发生。
我们对模拟和真实数据进行了高通滤波。我们还使用了两种替代方法：时频分析和匹配追踪。
两种类型的事件被证明在滤波后会产生振荡，这些振荡可能与实际的振荡活动混淆：尖锐瞬变和非正弦信号的谐波。
用于检测振荡活动的 EEG 迹线的高通滤波应谨慎进行。滤波迹线应与原始迹线进行比较，以验证瞬变的存在。时频变换或稀疏分解等附加技术非常有益。
我们的研究提请注意在 EEG 迹线上标记 HFOs 时非常重要的问题。我们说明了可以帮助研究人员和临床医生的补充方法。
