基于泛函MRI正则系综的脑建模：神经系统的热力学探索
Modelling brain based on canonical ensemble with functional MRI: A thermodynamic exploration on neural system
摘要：
Objective.模型化是研究大脑工作机制的重要手段。但对脑的表征和认识还不够。本研究尝试从系统层次上从热力学的角度来建立脑的模型，为脑的建模带来了新的思路。Approach.将脑区看作系统，体素看作粒子，信号强度看作粒子的能量，基于正则系综理论建立了脑的热力学模型。选取两对激活区和两对失活区进行比较，并基于所建模型进行热力学性质分析。此外，还提取了热力学性质作为阿尔茨海默病检测的输入特征。主要结果。实验结果验证了大脑也遵循热力学定律的假设。证明了所提出的脑热力学建模方法的可行性和合理性，表明热力学参数可以用来描述神经系统的状态。同时，脑热力学模型在阿尔茨海默病的检测中取得了更好的准确性，表明了热力学模型在辅助诊断中的潜在应用。意义(1)本文首次从热力学的角度提出了一个系统级的脑模型，而不是用一些热力学参数来分析神经系统。(2)研究发现，神经系统也遵循热力学定律，这导致系统激活时内能增加，自由能增加，熵减少。(3)热力学模型在神经系统疾病诊断中的应用，显示了热力学在辅助诊断中的巨大潜力。
英文摘要：
Objective. Modelling is an important way to study the working mechanism of brain. While the characterization and understanding of brain are still inadequate. This study tried to build a model of brain from the perspective of thermodynamics at system level, which brought a new thinking to brain modelling. Approach. Regarding brain regions as systems, voxels as particles, and intensity of signals as energy of particles, the thermodynamic model of brain was built based on canonical ensemble theory. Two pairs of activated regions and two pairs of inactivated brain regions were selected for comparison in this study, and the analysis on thermodynamic properties based on the model proposed were performed. In addition, the thermodynamic properties were also extracted as input features for the detection of Alzheimer's disease. Main results. The experiment results verified the assumption that the brain also follows the thermodynamic laws. It demonstrated the feasibility and rationality of brain thermodynamic modelling method proposed, indicating that thermodynamic parameters could be applied to describe the state of neural system. Meanwhile, the brain thermodynamic model achieved much better accuracy in detection of Alzheimer's disease, suggesting the potential application of thermodynamic model in auxiliary diagnosis. Significance. (1) Instead of applying some thermodynamic parameters to analyze neural system, a brain model at system level was proposed from perspective of thermodynamics for the first time in this study. (2) The study discovered that the neural system also follows the laws of thermodynamics, which leads to increased internal energy, increased free energy and decreased entropy when system is activated. (3) The detection of neural disease was demonstrated to be benefit from thermodynamic model, implying the immense potential of thermodynamics in auxiliary diagnosis.
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