Ramachandran V S, Rogers-Ramachandran D
Brain and Perception Laboratory, University of California, San Diego, La Jolla 92093, USA.
Proc Biol Sci. 1996 Apr 22;263(1369):377-86. doi: 10.1098/rspb.1996.0058.
Although there is a vast clinical literature on phantom limbs, there have been no experimental studies on the effects of visual input on phantom sensations. We introduce an inexpensive new device--a 'virtual reality box'--to resurrect the phantom visually to study inter-sensory effects. A mirror is placed vertically on the table so that the mirror reflection of the patient's intact had is 'superimposed' on the felt position of the phantom. We used this procedure on ten patients and found the following results. 1. In six patients, when the normal hand was moved, so that the phantom was perceived to move in the mirror, it was also felt to move; i.e. kinesthetic sensations emerged in the phantom. In D.S. this effect occurred even though he had never experienced any movements in the phantom for ten years before we tested him. He found the return of sensations very enjoyable. 2. Repeated practice led to a permanent 'disappearance' of the phantom arm in patient D.S. and the hand became telescoped into the stump near the shoulder. 3. Using an optical trick, impossible postures--e.g. extreme hyperextension of the fingers--could be induced visually in the phantom. In one case this was felt as a transient 'painful tug' in the phantom. 4. Five patients experienced involuntary painful 'clenching spasms' in the phantom hand and in four of them the spasms were relieved when the mirror was used to facilitate 'opening' of the phantom hand; opening was not possible without the mirror. 5. In three patients, touching the normal hand evoked precisely localized touch sensations in the phantom. Interestingly, the referral was especially pronounced when the patients actually 'saw' their phantom being touched in the mirror. Indeed, in a fourth patient (R.L.) the referral occurred only if he saw his phantom being touched: a curious form of synaesthesia. These experiments lend themselves readily to imaging studies using PET and fMRI. Taken collectively, they suggest that there is a considerable amount of latent plasticity even in the adult human brain. For example, precisely organized new pathways, bridging the two cerebral hemispheres, can emerge in less than three weeks. Furthermore, there must be a great deal of back and forth interaction between vision and touch, so that the strictly modular, hierarchical model of the brain that is currently in vogue needs to be replaced with a more dynamic, interactive model, in which 're-entrant' signalling plays the main role.
尽管关于幻肢已有大量临床文献，但尚无关于视觉输入对幻肢感觉影响的实验研究。我们引入了一种廉价的新设备——“虚拟现实箱”，以视觉方式重现幻肢，从而研究感觉间的相互作用。将一面镜子垂直放置在桌上，使患者完好手的镜像“叠加”在幻肢的感觉位置上。我们对10名患者采用了这一方法，得到以下结果。1. 6名患者中，当正常手移动时，幻肢在镜子中被感知到移动，同时也感觉它在动；即幻肢中出现了动觉。在D.S.身上，即便在测试前他已有10年未在幻肢中体验过任何动作，这种效应依然出现。他觉得感觉的恢复非常愉悦。2. 反复练习导致患者D.S.的幻肢臂永久“消失”，手缩进了靠近肩部的残肢中。3. 利用一个光学技巧，可以在幻肢中视觉诱导出不可能的姿势，比如手指极度伸展。有一例患者感觉幻肢中有短暂的“牵拉痛”。4. 5名患者在幻肢手中经历了非自主性疼痛性“紧握痉挛”，其中4名患者在使用镜子协助幻肢手“张开”时痉挛得到缓解；没有镜子则无法张开。5. 3名患者触摸正常手时，幻肢中会引发精确的局部触觉。有趣的是，当患者在镜子中实际“看到”幻肢被触摸时，这种牵涉痛尤其明显。事实上，第四名患者（R.L.）只有在看到幻肢被触摸时才会出现牵涉痛：一种奇特的联觉形式。这些实验很容易用于正电子发射断层扫描（PET）和功能磁共振成像（fMRI）的成像研究。总体而言，它们表明即使在成人大脑中也存在相当数量的潜在可塑性。例如，精确组织的连接两个脑半球的新通路可以在不到三周的时间内形成。此外，视觉和触觉之间必定存在大量的来回相互作用，因此当前流行的严格模块化、分层式大脑模型需要被一个更具动态性、交互性的模型所取代，其中“折返”信号起主要作用。
