Liu J Z, Yang Q, Yao B, Brown R W, Yue G H
Department of Biomedical Engineering, The Lerner Research Institute, The Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195, USA.
Biol Cybern. 2005 Aug;93(2):131-40. doi: 10.1007/s00422-005-0561-3. Epub 2005 Jul 18.
Fractal dimension (FD) has been proved useful in quantifying the complexity of dynamical signals in biology and medicine. In this study, we measured FDs of human electroencephalographic (EEG) signals at different levels of handgrip forces. EEG signals were recorded from five major motor-related cortical areas in eight normal healthy subjects. FDs were calculated using three different methods. The three physiological periods of handgrip (command preparation, movement and holding periods) were analyzed and compared. The results showed that FDs of the EEG signals during the movement and holding periods increased linearly with handgrip force, whereas FD during the preparation period had no correlation with force. The results also demonstrated that one method (Katz's) gave greater changes in FD, and thus, had more power in capturing the dynamic changes in the signal. The linear increase of FD, together with results from other EEG and neuroimaging studies, suggest that under normal conditions the brain recruits motor neurons at a linear progress when increasing the force.
分形维数（FD）已被证明在量化生物学和医学中动态信号的复杂性方面很有用。在本研究中，我们测量了不同握力水平下人类脑电图（EEG）信号的分形维数。从八名正常健康受试者的五个主要运动相关皮层区域记录了EEG信号。使用三种不同方法计算分形维数。对握力的三个生理时期（指令准备期、运动期和保持期）进行了分析和比较。结果表明，运动期和保持期EEG信号的分形维数随握力呈线性增加，而准备期的分形维数与力无关。结果还表明，一种方法（卡茨法）在分形维数上有更大变化，因此在捕捉信号动态变化方面更具效力。分形维数的线性增加，连同其他脑电图和神经影像学研究的结果，表明在正常情况下，大脑在增加力量时以线性方式募集运动神经元。
