意识是难以捉摸的，但我们知道它就是那个当我们进入深度睡眠时会消失而当我们醒来时会重新出现的东西。医生们常常会通过人们是否有能力对外部指令——如“睁开你的眼睛”，或“捏我的手”——进行处理并做出回应来决定一个人是否有意识。但这些方法都是肤浅的，因为在过去10年中的研究已经证明一个完全与外部环境隔绝联系的大脑仍然可以有某种程度的意识，这种情况也会发生在从昏迷中恢复但却无法移动或理解命令的脑部受伤的病人身上。一种理论认为，在有意识的大脑中，每个不同的神经元群都在起着其自身的特定的计算作用，但它们也仍然能够与其它的神经元群进行沟通。换句话说，它们会互动并计算。当大脑失去这种复杂性时，神经元或是会变得更为均一（从而导致信息的丧失）或者它们的沟通能力受到损害（从而导致整合能力的丧失）。例如，如果你睡着了并听到狗叫声，你的脑子会以听觉皮层的活动作为回应。但是，当你醒着，同样的叫声除了诱发听觉皮层的活动之外还会诱发你想到自己的狗以及对叫声之响感到讨厌——这些反应与脑子的记忆及情感中枢是挂钩的。后者的脑部处理过程含有更多的信息。神经科学家一直在尝试研发根据这种脑子的复杂性来检测意识的方法。
Marcello Massmini及其同事想出了一种新的方法来检测这种脑子的复杂性，或者说有多少整合及信息流动正在大脑中发生。他们的方法被称作扰动复杂性指数（PCI），它涉及用一个强力的磁刺激对整个脑子进行一次轻微的“震动”并记录神经元的反应。这些数据可接着被用来计算大脑作为一个整体能够产生的信息量。值得注意的是，该PCI无需患者从事任何的感觉、运动或认知的任务。研究人员在脑损伤病人、用不同药物进行麻醉的病人及在清醒、深度睡眠或做梦的病人中测试了这种技术。PCI反映了在每一种状态下参与者的意识水平。这些结果提示，不同的意识水平与大脑反应的复杂性有着紧密的联系。例如，发现在其它情况下完全没有反应的病人的PCI值高于睡眠或麻醉时的水平将提示她或他在一定程度上是有意识的。尽管需要做更多的研究，但这种PCI可能对于在医院的病床边检测病人的意识而言是一种有用的工具。（生物谷 Bioon.com）
生物谷推荐的英文摘要
Sci Transl Med DOI: 10.1126/scitranslmed.3006294
A Theoretically Based Index of Consciousness Independent of Sensory Processing and Behavior
Adenauer G. Casali1,*,†, Olivia Gosseries2,*, Mario Rosanova1, Mélanie Boly2,‡, Simone Sarasso1, Karina R. Casali1,3, Silvia Casarotto1, Marie-Aurélie Bruno2, Steven Laureys2, Giulio Tononi4 and Marcello Massimini
One challenging aspect of the clinical assessment of brain-injured, unresponsive patients is the lack of an objective measure of consciousness that is independent of the subject’s ability to interact with the external environment. Theoretical considerations suggest that consciousness depends on the brain’s ability to support complex activity patterns that are, at once, distributed among interacting cortical areas (integrated) and differentiated in space and time (information-rich). We introduce and test a theory-driven index of the level of consciousness called the perturbational complexity index (PCI). PCI is calculated by (i) perturbing the cortex with transcranial magnetic stimulation (TMS) to engage distributed interactions in the brain (integration) and (ii) compressing the spatiotemporal pattern of these electrocortical responses to measure their algorithmic complexity (information). We test PCI on a large data set of TMS-evoked potentials recorded in healthy subjects during wakefulness, dreaming, nonrapid eye movement sleep, and different levels of sedation induced by anesthetic agents (midazolam, xenon, and propofol), as well as in patients who had emerged from coma (vegetative state, minimally conscious state, and locked-in syndrome). PCI reliably discriminated the level of consciousness in single individuals during wakefulness, sleep, and anesthesia, as well as in patients who had emerged from coma and recovered a minimal level of consciousness. PCI can potentially be used for objective determination of the level of consciousness at the bedside.
