The brain is a functional unit made up of multi-level connected elements showing a pattern of synchronized activity that varies in different states. The wake-sleep cycle is a major variation of brain functional condition that is ultimately regulated by subcortical arousal- and sleep-promoting cell groups. We analyzed the evolution of functional MRI signal in the whole cortex and in a deep region including most sleep- and wake-regulating subcortical nuclei at loss of consciousness induced by the hypnotic agent propofol. Optimal data were obtained in 21 of the 30 healthy participants examined. A dynamic analysis of functional MRI time courses on a time-scale of seconds was conducted to characterize consciousness transition, and functional connectivity maps were generated to detail the anatomy of structures showing different dynamics. Inside the magnet, loss of consciousness was marked by the participants ceasing to move their hands. We observed activity synchronization after loss of consciousness within both the cerebral cortex and subcortical structures. However, the evolution of functional MRI signal was dissociated, showing a transient reduction of global cortico-subcortical coupling that was restored during the unconscious state. An exception to cortico-subcortical decoupling was a brain network related to self-awareness (i.e., the default mode network) that remained connected to subcortical brain structures. Propofol-induced unconsciousness is thus characterized by an initial, transitory dissociated synchronization at the largest scale of brain activity. Such cortico-subcortical decoupling and subsequent re-coupling may allow the brain to detach from waking activity and reorganize into a functionally distinct state.

中文翻译：

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丙泊酚引起的意识丧失时大脑活动的最大规模分离

大脑是一个由多层次连接元素组成的功能单元，显示出在不同状态下变化的同步活动模式。唤醒-睡眠周期是大脑功能状况的主要变化，最终由皮层下唤醒和睡眠促进细胞群调节。我们分析了整个皮层和深部区域的功能性 MRI 信号的演变，包括大多数睡眠和唤醒调节皮质下核在由催眠药丙泊酚引起的意识丧失时。在接受检查的 30 名健康参与者中，有 21 名获得了最佳数据。以秒为时间尺度对功能性 MRI 时间进程进行动态分析以表征意识转变，并生成功能连接图以详细描述显示不同动态的结构的解剖结构。在磁铁内部，参与者停止移动他们的手标志着意识丧失。我们在大脑皮层和皮层下结构中观察到意识丧失后的活动同步。然而，功能性 MRI 信号的演变是分离的，显示出在无意识状态期间恢复的全局皮质-皮质下耦合的短暂减少。皮质-皮质下解耦的一个例外是与自我意识相关的大脑网络（即默认模式网络），它与皮质下大脑结构保持连接。因此，丙泊酚引起的无意识的特点是在大脑活动的最大范围内出现初始的、短暂的分离同步。