Ma Matthew King-Hang, Fong Manson Cheuk-Man, Xie Chenwei, Lee Tan, Chen Guanrong, Wang William Shiyuan
Department of Electronic Engineering, The Chinese University of Hong Kong, Hong Kong.
Research Centre for Language, Cognition, and Neuroscience, Department of Chinese and Bilingual Studies, The Hong Kong Polytechnic University, Hong Kong.
Neuroimage Rep. 2021 Sep 28;1(4):100054. doi: 10.1016/j.ynirp.2021.100054. eCollection 2021 Dec.
The loss of complexity in ageing hypothesis (LOCH) has found support from EEG studies, most of which adopted signal-domain complexity measures. The present study adopted the largest Lyapunov exponent (LLE) to measure complexity from a nonlinear dynamical systems perspective. A total of 144 participants were included and divided into young, young-old and old-old groups. Both sensor-space and source-space results showed significantly lower LLE for older than younger adults. The age-related differences were region-dependent, being most prominent in the frontal region, followed by bilateral temporal regions. The occipital region showed non-significant differences. Significant reduction of LLE in the posterior cingulate was also observed by virtue of the source-space analysis. We also evaluated the relationships between LLE and other complexity measures. The most intriguing result was the negative correlation between LLE and Lempel-Ziv complexity (LZC). The age-related decrease in LLE indicated a higher regularity in dynamics, while the higher LZC indicated a higher randomness in the signal domain. The new findings support the LOCH by demonstrating the simultaneous increase in regularity and randomness.
衰老复杂性丧失假说（LOCH）已得到脑电图研究的支持，其中大多数研究采用信号域复杂性测量方法。本研究采用最大Lyapunov指数（LLE）从非线性动力系统角度测量复杂性。总共纳入了144名参与者，并将其分为青年组、年轻老年组和老年组。传感器空间和源空间的结果均显示，老年人的LLE显著低于年轻人。与年龄相关的差异具有区域依赖性，在额叶区域最为明显，其次是双侧颞叶区域。枕叶区域未显示出显著差异。通过源空间分析还观察到后扣带回的LLE显著降低。我们还评估了LLE与其他复杂性测量之间的关系。最有趣的结果是LLE与Lempel-Ziv复杂性（LZC）之间呈负相关。与年龄相关的LLE降低表明动力学具有更高的规律性，而较高的LZC表明信号域具有更高的随机性。这些新发现通过证明规律性和随机性同时增加，支持了衰老复杂性丧失假说。
