Onton Julie, Delorme Arnaud, Makeig Scott
Swartz Center for Computational Neuroscience, Institute for Neural Computation, University of California San Diego, La Jolla, CA 92093-0961, USA.
Neuroimage. 2005 Aug 15;27(2):341-56. doi: 10.1016/j.neuroimage.2005.04.014.
We show that during visual working memory, the electroencephalographic (EEG) process producing 5-7 Hz frontal midline theta (fmtheta) activity exhibits multiple spectral modes involving at least three frequency bands and a wide range of amplitudes. The process accounting for the fmtheta increase during working memory was separated from 71-channel data by clustering on time/frequency transforms of components returned by independent component analysis (ICA). Dipole models of fmtheta component scalp maps were consistent with their generation in or near dorsal anterior cingulate cortex. From trial to trial, theta power of fmtheta components varied widely but correlated moderately with theta power in other frontal and left temporal processes. The weak mean increase in frontal midline theta power with increasing memory load, produced entirely by the fmtheta components, largely reflected progressively stronger theta activity in a relatively small proportion of trials. During presentations of letter series to be memorized or ignored, fmtheta components also exhibited 12-15 Hz low-beta activity that was stronger during memorized than during ignored letter trials, independent of letter duration. The same components produced a brief 3-Hz burst 500 ms after onset of the Probe letter following each letter sequence. A new decomposition method, log spectral ICA, applied to normalized log time/frequency transforms of fmtheta component Memorize-letter trials, showed that their low-beta activity reflected harmonic energy in continuous, sharp-peaked theta wave trains as well as independent low-beta bursts. Possibly, the observed fmtheta process variability may index dynamic adjustments in medial frontal cortex to trial-specific behavioral context and task demands.
我们发现，在视觉工作记忆期间，产生5-7赫兹额中theta波（fmtheta）活动的脑电图（EEG）过程呈现出多种频谱模式，涉及至少三个频段和广泛的振幅范围。通过对独立成分分析（ICA）返回的成分进行时间/频率变换聚类，从71通道数据中分离出了在工作记忆期间导致fmtheta增加的过程。fmtheta成分头皮图的偶极子模型与其在背侧前扣带回皮质或其附近的产生一致。在每次试验中，fmtheta成分的theta功率变化很大，但与其他额叶和左侧颞叶过程中的theta功率呈中度相关。随着记忆负荷增加，额中theta功率的微弱平均增加完全由fmtheta成分产生，这在很大程度上反映了在相对较小比例的试验中theta活动逐渐增强。在呈现要记忆或忽略的字母序列时，fmtheta成分还表现出12-15赫兹的低β活动，在记忆字母试验期间比在忽略字母试验期间更强，与字母持续时间无关。在每个字母序列后的探测字母出现500毫秒后，相同的成分产生了一个短暂的3赫兹爆发。一种新的分解方法，对数频谱ICA，应用于fmtheta成分记忆字母试验的归一化对数时间/频率变换，结果表明其低β活动反映了连续、尖峰theta波列中的谐波能量以及独立的低β爆发。可能，观察到的fmtheta过程变异性可能指示内侧额叶皮质对特定试验行为背景和任务需求的动态调整。
