Plum F, Schiff N, Ribary U, Llinás R
Cornell University Medical College, New York Presbyterian Hospital, NY 10021, USA.
Philos Trans R Soc Lond B Biol Sci. 1998 Nov 29;353(1377):1929-33. doi: 10.1098/rstb.1998.0345.
The clinically described 'persistent vegetative state' (PVS), consists of wakefulness unaccompanied by any evidence of the subject's awareness of self or environment. Past studies from our own and other laboratories have used positron emission tomography (PET) to study brain metabolism in approximately 20 such patients during wakeful periods. All those efforts identified global cerebral glucose metabolism at or below levels encountered during deep barbiturate anaesthesia. Nevertheless, the clinical literature includes rare reports of relatively isolated cognitive functions expressed by PVS patients late in their course. The observation raises the question of whether such activity reflects awareness or unconscious automatic behaviour. We employed magnetometry (MEG), PET scanning, MR imaging and 24-hour EEG recordings to evaluate three patients clinically vegetative between six months and 20 years after onset. Neither meticulous clinical examinations nor 24-hour EEG and video monitoring provided any hint of cognitive interaction in any subject. Nevertheless, patient 1 uttered single words once every 48 hours or more; patient 2 frequently expressed coordinated, non-purposeful, non-dystonic movements in arms and/or legs; and, patient 3 expressed strong emotional negativity without motor responses to noxious stimuli with occasional quieting in response to prosodic stimuli. All patients had whole-brain averaged global metabolism levels below 50% of normal. Patient 1, however, demonstrated preserved islands of increased metabolism in the posterior frontal and posterior temporal lobes, as well as MEG activations of Heschl's gyrus all located in the left hemisphere. In patient 2, selected increased metabolism was confined to the frontal poles and related subcortical structures. MRI in patient 3 demonstrated severe, bilateral post-traumatic cerebral atrophy. PET metabolism was diffusely reduced to 40% of normal but MEG evoked potentials indicated early and late sensory processing with abnormal later evoked components. The correlation of fragmentary behaviour with preserved metabolic and physiologic activity in cortical and subcortical regions known to support specific modular functions is novel. The finding demonstrates the capacity of severely damaged brains to partially express surviving modular functions without evidence of integrative processes that would be necessary to produce consciousness. We conclude that the mere expression of isolated neuropsychologic activity by isolated modules is insufficient to generate consciousness in overwhelmingly damaged brains.
临床上所描述的“持续性植物状态”（PVS），其特征为清醒状态，但没有任何证据表明患者对自我或环境有认知。我们自己的实验室以及其他实验室过去的研究，已使用正电子发射断层扫描（PET）来研究大约20例处于清醒期的此类患者的脑代谢情况。所有这些研究均发现，全脑葡萄糖代谢处于或低于深度巴比妥类麻醉期间的水平。然而，临床文献中罕见关于PVS患者病程后期表现出相对孤立认知功能的报道。这一观察结果引发了一个问题，即这种活动是反映了意识还是无意识的自动行为。我们采用了磁强计（MEG）、PET扫描、磁共振成像（MR）和24小时脑电图记录，对3例发病后6个月至20年处于临床植物状态的患者进行评估。无论是细致的临床检查，还是24小时脑电图和视频监测，均未在任何患者中发现认知交互的任何迹象。然而，患者1每48小时或更长时间会说出单个单词；患者2频繁表现出手臂和/或腿部协调、无目的、无张力障碍的运动；患者3表现出强烈的负面情绪，对有害刺激无运动反应，但偶尔会因韵律刺激而安静下来。所有患者全脑平均整体代谢水平均低于正常水平的50%。然而，患者1在额叶后部和颞叶后部显示出代谢增加的保留岛状区域，以及位于左半球的Heschl回的MEG激活。在患者2中，选定的代谢增加局限于额极和相关的皮质下结构。患者3的磁共振成像显示严重的双侧创伤后脑萎缩。PET代谢广泛降低至正常水平的40%，但MEG诱发电位表明存在早期和晚期感觉处理，后期诱发电位成分异常。已知支持特定模块功能的皮质和皮质下区域中，零碎行为与保留的代谢和生理活动之间的相关性是新颖的。这一发现表明，严重受损的大脑有能力部分表达幸存的模块功能，而无需产生意识所需的整合过程的证据。我们得出结论，在严重受损的大脑中，仅仅由孤立模块表达孤立的神经心理活动不足以产生意识。
