Institute of Biomedical Research August Pi i Sunyer (IDIBAPS), Barcelona, 08036, Spain.
Centre for Eudaimonia and Human Flourishing, University of Oxford, Oxford, OX3 9BX, UK.
Sci Rep. 2024 Oct 16;14(1):24271. doi: 10.1038/s41598-024-74649-1.
The brain is a complex non-equilibrium system capable of expressing many different dynamics as well as the transitions between them. We hypothesized that the level of non-equilibrium can serve as a signature of a given brain state, which was quantified using the arrow of time (the level of irreversibility). Using this thermodynamic framework, the irreversibility of emergent cortical activity was quantified from local field potential recordings in male Lister-hooded rats at different anesthesia levels and during the sleep-wake cycle. This measure was carried out on five distinct brain states: slow-wave sleep, awake, deep anesthesia-slow waves, light anesthesia-slow waves, and microarousals. Low levels of irreversibility were associated with synchronous activity found both in deep anesthesia and slow-wave sleep states, suggesting that slow waves were the state closest to the thermodynamic equilibrium (maximum symmetry), thus requiring minimum energy. Higher levels of irreversibility were found when brain dynamics became more asynchronous, for example, in wakefulness. These changes were also reflected in the hierarchy of cortical dynamics across different cortical areas. The neural dynamics associated with different brain states were characterized by different degrees of irreversibility and hierarchy, also acting as markers of brain state transitions. This could open new routes to monitoring, controlling, and even changing brain states in health and disease.
大脑是一个复杂的非平衡系统，能够表达许多不同的动力学以及它们之间的转变。我们假设非平衡水平可以作为特定大脑状态的特征，这可以通过时间箭头（不可逆性水平）来量化。使用这个热力学框架，从不同麻醉水平和睡眠-觉醒周期的雄性 Lister-hooded 大鼠的局部场电位记录中量化了新兴皮质活动的不可逆性。这项测量是在五个不同的大脑状态下进行的：慢波睡眠、清醒、深度麻醉-慢波、轻度麻醉-慢波和微觉醒。不可逆性水平低与深度麻醉和慢波睡眠状态下发现的同步活动有关，这表明慢波是最接近热力学平衡（最大对称性）的状态，因此需要最小的能量。当大脑动力学变得更加异步时，例如在清醒状态下，会发现更高水平的不可逆性。这些变化也反映在不同皮质区域的皮质动力学层次结构中。与不同大脑状态相关的神经动力学具有不同程度的不可逆性和层次结构，也可以作为大脑状态转变的标志物。这可能为在健康和疾病中监测、控制甚至改变大脑状态开辟新的途径。
