Neural Circuits and Cognition Unit, Laboratory of Behavioral Neuroscience, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA.
Neural Circuits and Cognition Unit, Laboratory of Behavioral Neuroscience, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA.
Neuroimage. 2016 May 15;132:79-92. doi: 10.1016/j.neuroimage.2016.02.032. Epub 2016 Feb 16.
Local field potentials (LFPs) are commonly thought to reflect the aggregate dynamics in local neural circuits around recording electrodes. However, we show that when LFPs are recorded in awake behaving animals against a distal reference on the skull as commonly practiced, LFPs are significantly contaminated by non-local and non-neural sources arising from the reference electrode and from movement-related noise. In a data set with simultaneously recorded LFPs and electroencephalograms (EEGs) across multiple brain regions while rats perform an auditory oddball task, we used independent component analysis (ICA) to identify signals arising from electrical reference and from volume-conducted noise based on their distributed spatial pattern across multiple electrodes and distinct power spectral features. These sources of distal electrical signals collectively accounted for 23-77% of total variance in unprocessed LFPs, as well as most of the gamma oscillation responses to the target stimulus in EEGs. Gamma oscillation power was concentrated in volume-conducted noise and was tightly coupled with the onset of licking behavior, suggesting a likely origin of muscle activity associated with body movement or orofacial movement. The removal of distal signal contamination also selectively reduced correlations of LFP/EEG signals between distant brain regions but not within the same region. Finally, the removal of contamination from distal electrical signals preserved an event-related potential (ERP) response to auditory stimuli in the frontal cortex and also increased the coupling between the frontal ERP amplitude and neuronal activity in the basal forebrain, supporting the conclusion that removing distal electrical signals unmasked local activity within LFPs. Together, these results highlight the significant contamination of LFPs by distal electrical signals and caution against the straightforward interpretation of unprocessed LFPs. Our results provide a principled approach to identify and remove such contamination to unmask local LFPs.
局部场电位（LFPs）通常被认为反映了记录电极周围局部神经回路的总体动态。然而，我们表明，当 LFPs 在清醒活动的动物中记录时，使用颅骨上的远端参考作为常见的参考，LFPs 会受到来自参考电极和与运动相关的噪声的非局部和非神经源的显著污染。在一组大鼠在执行听觉Oddball 任务时同时记录多个脑区的 LFPs 和脑电图（EEGs）的数据集中，我们使用独立成分分析（ICA）根据其在多个电极上的分布式空间模式和独特的功率谱特征，来识别来自电参考和体积传导噪声的信号。这些远端电信号源共同解释了未经处理的 LFPs 总方差的 23-77%，以及 EEG 中对目标刺激的大部分伽马振荡反应。伽马振荡功率集中在体积传导噪声中，与舔舐行为的开始紧密耦合，表明与身体运动或口面部运动相关的肌肉活动的可能来源。去除远端信号污染还选择性地降低了大脑不同区域之间的 LFPs/EEG 信号的相关性，但不影响同一区域内的相关性。最后，去除远端电信号的污染保留了额叶皮层对听觉刺激的事件相关电位（ERP）反应，并且增加了额叶 ERP 幅度与基底前脑神经元活动之间的耦合，支持了去除远端电信号揭示 LFPs 中局部活动的结论。总之，这些结果强调了 LFPs 受到远端电信号的显著污染，并告诫人们不要直接解释未经处理的 LFPs。我们的结果提供了一种识别和去除这种污染以揭示局部 LFPs 的原则性方法。
