Department of Anesthesiology and Center for Consciousness Science, University of Michigan, Ann Arbor, Michigan.
Department of Anesthesiology, Huashan Hospital, Fudan University, Shanghai, People's Republic of China.
Hum Brain Mapp. 2018 Nov;39(11):4533-4544. doi: 10.1002/hbm.24304. Epub 2018 Jul 4.
Variability quenching is a widespread neural phenomenon in which trial-to-trial variability (TTV) of neural activity is reduced by repeated presentations of a sensory stimulus. However, its neural mechanism and functional significance remain poorly understood. Recurrent network dynamics are suggested as a candidate mechanism of TTV, and they play a key role in consciousness. We thus asked whether the variability-quenching phenomenon is related to the level of consciousness. We hypothesized that TTV reduction would be compromised during reduced level of consciousness by propofol anesthetics. We recorded functional magnetic resonance imaging signals of resting-state and stimulus-induced activities in three conditions: wakefulness, sedation, and unconsciousness (i.e., deep anesthesia). We measured the average (trial-to-trial mean, TTM) and variability (TTV) of auditory stimulus-induced activity under the three conditions. We also examined another form of neural variability (temporal variability, TV), which quantifies the overall dynamic range of ongoing neural activity across time, during both the resting-state and the task. We found that (a) TTM deceased gradually from wakefulness through sedation to anesthesia, (b) stimulus-induced TTV reduction normally seen during wakefulness was abolished during both sedation and anesthesia, and (c) TV increased in the task state as compared to resting-state during both wakefulness and sedation, but not anesthesia. Together, our results reveal distinct effects of propofol on the two forms of neural variability (TTV and TV). They imply that the anesthetic disrupts recurrent network dynamics, thus prevents the stabilization of cortical activity states. These findings shed new light on the temporal dynamics of neuronal variability and its alteration during anesthetic-induced unconsciousness.
变异性淬火是一种广泛存在的神经现象，即在重复呈现感觉刺激时，神经活动的trial-to-trial 变异性（TTV）降低。然而，其神经机制和功能意义仍知之甚少。递归网络动力学被认为是 TTV 的候选机制，并且在意识中起着关键作用。因此，我们想知道变异性淬火现象是否与意识水平有关。我们假设，在意识水平降低的情况下，丙泊酚麻醉剂会损害 TTV 降低。我们记录了三种状态下静息状态和刺激诱导活动的功能磁共振成像信号：清醒、镇静和无意识（即深度麻醉）。我们测量了三种条件下听觉刺激诱导活动的平均（trial-to-trial mean，TTM）和变异性（TTV）。我们还检查了另一种形式的神经变异性（时间变异性，TV），它量化了在静息状态和任务期间整个时间内持续神经活动的整体动态范围。我们发现：（a）TTM 从清醒状态逐渐下降到镇静状态再到麻醉状态；（b）在镇静和麻醉期间，正常情况下在清醒状态下观察到的刺激诱导 TTV 降低被消除；（c）与静息状态相比，在清醒和镇静状态下，任务状态下的 TV 增加，但在麻醉状态下没有增加。总之，我们的结果揭示了丙泊酚对两种神经变异性（TTV 和 TV）的不同影响。它们意味着麻醉剂破坏了递归网络动力学，从而阻止了皮质活动状态的稳定。这些发现为神经元变异性的时间动态及其在麻醉诱导无意识期间的改变提供了新的认识。
