健忘症患者总是在拼命回忆自己的过去。然而根据一项新的研究,他们可能还在费力地设想自己的未来。研究人员发现,因海马状突起(海马区)——与记忆密切相关的大脑区域——受损而患上记忆缺失的病人,很难想象新的经历。
在这项研究中,英国伦敦大学学院的认知神经学家Eleanor Maguire和同事对5名健忘症患者进行了监测。所有这些患者都是由于大脑海马状突起受损而导致严重的记忆障碍——他们很难形成新的记忆,并且无法记住大脑受伤后发生的事情。有10名与这些健忘症患者的年龄和受教育水平相仿的正常人作为对照组参与了此项研究。这项研究成果发表于本周的美国《国家科学院院刊》网络版上。
Maguire的研究小组要求每一名受试者想象并描述他们在未来有可能遇到的几个普通场景,例如碰见一个朋友或是去海滨游玩、去酒吧喝酒、去超市购物。健康的受试者均给出了丰富的描述,例如他们谈到海岸的曲线、海浪拍打岸边的声音以及脚踩炙热沙滩的感觉。而健忘症患者虽然能够按照研究人员的意图去做,但他们的描述却要生涩得多。与健康的志愿者相比,健忘症患者只提及了较少的事物和感觉细节,例如声音和气味,以及较少的因想象的场景而产生的想法和情绪。通过健忘症患者完成的一份调查问卷,研究人员发现,他们所想象的都是一些景象的碎片而非一幅完成的画面。
美国图森市亚利桑那大学的认知神经学家Lynn Nadel表示,这一发现对传统的教科书形成了挑战,前者将海马状突起的主要功能描述为编码新的记忆。Nadel指出:“这项研究成果表明,我们能够利用相同的系统回忆过去并构建可能的未来。”加拿大多伦多大学的认知神经学家Morris Moscovitch表示,Maguire的工作同时也印证了其他科学家最近取得的研究成果——海马状突起能够将一些场景的要素结合在一起,从而在脑海中形成一幅连贯的画面。Moscovitch指出:“如果想要生动地构建过去、未来或者想象的事物,那你绝对离不开海马状突起。”
英文原文:
Stuck in the Present
People with amnesia struggle to remember their past. They may also struggle to envision their future, according to a new study. Researchers have found that people with amnesia caused by damage to the hippocampus, a brain region intimately tied to memory, have difficulty imagining new experiences.
In the new study, published online this week by the Proceedings of the National Academy of Sciences, cognitive neuroscientist Eleanor Maguire at University College London and colleagues examined five amnesic patients. All of them had severe memory deficits caused by damage to the hippocampus; they had great difficulty forming new memories and recalling events that occurred after their injuries. Ten healthy individuals who matched the patients' ages and education levels participated in the study as controls.
Maguire's team asked each subject to imagine and describe several commonplace scenarios they might reasonably expect to encounter in the future, such as meeting a friend or visiting a beach, a pub, or a market. The healthy subjects provided rich descriptions, remarking for example on the curve of a beach, the sound of waves hitting the shore, and the feel of burning hot sand. The amnesic patients were able to follow the researchers' instructions, but their descriptions were far less vivid. Compared to healthy subjects, the patients described fewer objects, fewer sensory details such as sounds and smells, and fewer thoughts or emotions that might be evoked in the imagined scenario. The patients' responses on a questionnaire indicated that what they saw in their mind's eye were fragmented collections of images rather than coherent scenes.
The findings challenge the traditional textbook view that the main job of the hippocampus is to encode new memories, says Lynn Nadel, a cognitive neuroscientist at the University of Arizona in Tucson. "The claim here is that the same system we use to remember the past we also use to construct possible futures," he says. Maguire's study fits with other recent work suggesting that the hippocampus binds together the elements of a scene to create a coherent mental picture, says Morris Moscovitch, a cognitive neuroscientist at the University of Toronto in Canada. "In order to have vivid constructions of the past, the future, or of imaginary events, you always need the hippocampus," he says.