Fractal dimension of cortical functional connectivity networks & severity of disorders of consciousness
Fractal dimension of cortical functional connectivity networks & severity of disorders of consciousness
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DOI：
10.1371/journal.pone.0223812
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发表时间：
2020-02-13
期刊：
影响因子：
3.7
通讯作者：
Stamatakis, Emmanuel A.
中科院分区：
文献类型：
--
作者：
Varley, Thomas F.;Craig, Michael;Stamatakis, Emmanuel A.
最近的证据表明，意识体验的数量和质量可能是大脑活动复杂性的函数，意识出现在低熵和高熵状态之间的临界区域。我们提出分形形状作为接近这一临界点的一个措施，分形维数编码信息的复杂性超出简单的熵或随机性，分形结构是已知的出现在系统接近临界点。为了验证这一点，我们测试了健康志愿者和不同严重程度的意识障碍患者的大脑活动的分形维数的几个措施。我们使用了紧凑的烧盒算法来计算皮质功能连接网络的分形维数，以及使用二维盒计数算法来计算相关邻接矩阵的分形维数。为了测试大脑活动是否在时间和空间上都是分形的，我们在BOLD时间序列上使用了Higuchi时间分形维数。我们发现健康志愿者（n = 15），处于最低意识状态的患者（n = 10）和处于植物人状态的患者（n = 8）之间的分形维数显著降低，无论损伤机制如何。我们还发现邻接矩阵分形维数和Higuchi时间分形维数显着下降，这与意识水平下降。这些结果表明，皮质功能连接网络显示分形特征，这与临床相关人群的意识水平有关，更高的分形维数（即更复杂）的网络与更高的意识水平有关。这支持了意识水平和系统复杂性正相关的假设，并且与先前的EEG，MEG和fMRI研究一致。
Recent evidence suggests that the quantity and quality of conscious experience may be a function of the complexity of activity in the brain and that consciousness emerges in a critical zone between low and high-entropy states. We propose fractal shapes as a measure of proximity to this critical point, as fractal dimension encodes information about complexity beyond simple entropy or randomness, and fractal structures are known to emerge in systems nearing a critical point. To validate this, we tested several measures of fractal dimension on the brain activity from healthy volunteers and patients with disorders of consciousness of varying severity. We used a Compact Box Burning algorithm to compute the fractal dimension of cortical functional connectivity networks as well as computing the fractal dimension of the associated adjacency matrices using a 2D box-counting algorithm. To test whether brain activity is fractal in time as well as space, we used the Higuchi temporal fractal dimension on BOLD time-series. We found significant decreases in the fractal dimension between healthy volunteers (n = 15), patients in a minimally conscious state (n = 10), and patients in a vegetative state (n = 8), regardless of the mechanism of injury. We also found significant decreases in adjacency matrix fractal dimension and Higuchi temporal fractal dimension, which correlated with decreasing level of consciousness. These results suggest that cortical functional connectivity networks display fractal character and that this is associated with level of consciousness in a clinically relevant population, with higher fractal dimensions (i.e. more complex) networks being associated with higher levels of consciousness. This supports the hypothesis that level of consciousness and system complexity are positively associated, and is consistent with previous EEG, MEG, and fMRI studies.