意識是難以捉摸的,，但我們知道它就是那個(gè)當(dāng)我們進(jìn)入深度睡眠時(shí)會消失而當(dāng)我們醒來時(shí)會重新出現(xiàn)的東西,。醫(yī)生們常常會通過人們是否有能力對外部指令——如“睜開你的眼睛”，或“捏我的手”——進(jìn)行處理并做出回應(yīng)來決定一個(gè)人是否有意識,。但這些方法都是膚淺的,，因?yàn)樵谶^去10年中的研究已經(jīng)證明一個(gè)完全與外部環(huán)境隔絕聯(lián)系的大腦仍然可以有某種程度的意識，這種情況也會發(fā)生在從昏迷中恢復(fù)但卻無法移動或理解命令的腦部受傷的病人身上,。一種理論認(rèn)為,，在有意識的大腦中,，每個(gè)不同的神經(jīng)元群都在起著其自身的特定的計(jì)算作用，但它們也仍然能夠與其它的神經(jīng)元群進(jìn)行溝通,。換句話說,，它們會互動并計(jì)算,。當(dāng)大腦失去這種復(fù)雜性時(shí),，神經(jīng)元或是會變得更為均一（從而導(dǎo)致信息的喪失）或者它們的溝通能力受到損害（從而導(dǎo)致整合能力的喪失）。例如,，如果你睡著了并聽到狗叫聲,，你的腦子會以聽覺皮層的活動作為回應(yīng)。但是,，當(dāng)你醒著,，同樣的叫聲除了誘發(fā)聽覺皮層的活動之外還會誘發(fā)你想到自己的狗以及對叫聲之響感到討厭——這些反應(yīng)與腦子的記憶及情感中樞是掛鉤的。后者的腦部處理過程含有更多的信息,。神經(jīng)科學(xué)家一直在嘗試研發(fā)根據(jù)這種腦子的復(fù)雜性來檢測意識的方法,。
Marcello Massmini及其同事想出了一種新的方法來檢測這種腦子的復(fù)雜性，或者說有多少整合及信息流動正在大腦中發(fā)生,。他們的方法被稱作擾動復(fù)雜性指數(shù)（PCI）,，它涉及用一個(gè)強(qiáng)力的磁刺激對整個(gè)腦子進(jìn)行一次輕微的“震動”并記錄神經(jīng)元的反應(yīng)。這些數(shù)據(jù)可接著被用來計(jì)算大腦作為一個(gè)整體能夠產(chǎn)生的信息量,。值得注意的是,，該P(yáng)CI無需患者從事任何的感覺、運(yùn)動或認(rèn)知的任務(wù),。研究人員在腦損傷病人,、用不同藥物進(jìn)行麻醉的病人及在清醒、深度睡眠或做夢的病人中測試了這種技術(shù),。PCI反映了在每一種狀態(tài)下參與者的意識水平,。這些結(jié)果提示，不同的意識水平與大腦反應(yīng)的復(fù)雜性有著緊密的聯(lián)系,。例如,，發(fā)現(xiàn)在其它情況下完全沒有反應(yīng)的病人的PCI值高于睡眠或麻醉時(shí)的水平將提示她或他在一定程度上是有意識的。盡管需要做更多的研究,，但這種PCI可能對于在醫(yī)院的病床邊檢測病人的意識而言是一種有用的工具,。（生物谷 Bioon.com）
生物谷推薦的英文摘要
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.
