Whether the brain operates at a critical “tipping” point is a long standing scientific question, with evidence from both cellular and systems-scale studies suggesting that the brain does sit in, or near, a critical regime. Neuroimaging studies of humans in altered states of consciousness have prompted the suggestion that maintenance of critical dynamics is necessary for the emergence of consciousness and complex cognition, and that reduced or disorganized consciousness may be associated with deviations from criticality. Unfortunately, many of the cellular-level studies reporting signs of criticality were performed in non-conscious systems (in vitro neuronal cultures) or unconscious animals (e.g. anaesthetized rats). Here we attempted to address this knowledge gap by exploring critical brain dynamics in invasive ECoG recordings from multiple sessions with a single macaque as the animal transitioned from consciousness to unconsciousness under different anaesthetics (ketamine and propofol). We use a previously-validated test of criticality: avalanche dynamics to assess the differences in brain dynamics between normal consciousness and both drug-states. Propofol and ketamine were selected due to their differential effects on consciousness (ketamine, but not propofol, is known to induce an unusual state known as “dissociative anaesthesia”). Our analyses indicate that propofol dramatically restricted the size and duration of avalanches, while ketamine allowed for more awake-like dynamics to persist. In addition, propofol, but not ketamine, triggered a large reduction in the complexity of brain dynamics. All states, however, showed some signs of persistent criticality when testing for exponent relations and universal shape-collapse. Further, maintenance of critical brain dynamics may be important for regulation and control of conscious awareness.

大脑是否在关键的“临界点”运行是一个长期存在的科学问题，来自细胞和系统规模研究的证据表明，大脑确实处于或接近一个关键状态。对意识状态改变的人类进行的神经影像学研究提示，维持临界动态对于意识和复杂认知的出现是必要的，意识的减少或混乱可能与偏离临界性有关。不幸的是，许多报告危急迹象的细胞水平研究是在无意识系统（体外神经元培养物）或无意识动物（例如麻醉大鼠）中进行的。在这里，我们试图通过探索在不同麻醉剂（氯胺酮和异丙酚）下从有意识转变为无意识状态下一只猕猴的多次侵入性 ECoG 记录中的关键大脑动态来解决这一知识差距。我们使用先前验证的临界性测试：雪崩动力学来评估正常意识和两种药物状态之间的大脑动力学差异。选择异丙酚和氯胺酮是因为它们对意识的影响不同（已知氯胺酮而非异丙酚会诱发一种称为“解离性麻醉”的不寻常状态）。我们的分析表明，异丙酚极大地限制了雪崩的规模和持续时间，而氯胺酮则允许更多类似清醒的动态持续存在。此外，异丙酚（而不是氯胺酮）引发了大脑动力学复杂性的大幅降​​低。然而，在测试指数关系和通用形状崩溃时，所有状态都表现出了一些持续关键的迹象。 此外，维持关键的大脑动态对于意识意识的调节和控制可能很重要。