盲人的听力为什么那么好

Blind Visual Cortex

人类大脑具有超强的适应能力,我们的人生经历在不断塑造我们的大脑。其中一个突出案例就是,盲人大脑的视觉皮层会被赋予新功能,用来处理听觉任务,比如检测物体运动,确定声音来源。但这些新功能可能更为复杂。问题是,先天性失明的人,他们大脑的这部分功能究竟会有多大改变?约翰霍普金斯大学认知神经学家玛丽娜说。

她和团队让盲人和视力健全者一边听娱乐电影中的音频片段,一边对其进行脑部功能磁共振扫描。研究目的是找出盲人的视觉皮层是否被持续激活,以处理复杂的听觉任务。我们将其中一人的大脑活动和另一个人的大脑活动关联起来。这样一来,当大脑受到一段给定音频刺激时,我们就能直接比较两个大脑信息处理的相似度。比如,我们可由此得知,不同盲人的视觉皮层是否在同一时间做同一件事。结果表明,拥有大量大脑皮层的大脑枕叶,超过百分之六十五的区域出现高度同步。换句话讲,盲人受试者中,大部分视觉皮层区域被电影音频同时激活。但视力健全者的视觉皮层并没有同时激活。

而且,如果电影片段是胡乱拼凑、毫无意义的,盲人受试者表现出的相似性大大降低。这项研究结果表明,视觉皮层不只是一个简单的声音处理器官。这点非尤为重要,因为这意味着这片大脑区域很可能从低级的感知区变成了高级的认知区。也就是说,这片区域有着极高的重组性和可塑性。这项研究发表在神经科学期刊上。

科学家将进一步研究,其它人生经历,比如阅读盲文、电脑编程等等,是否也会对认知功能产生巨大影响。

原文

The human brain is remarkably adaptable, constantly being shaped by life experience. A striking example is that in blind people, the brain’s visual cortex is repurposed for auditory tasks—such as detecting motion and pinpointing where a sound is coming from. But its adopted functions could be even more complex. “And the question is, well: How much can this part of the brain change its function in people who were born blind?”Johns Hopkins cognitive neuroscientist Marina Bedny.

She and her team had blind and sighted volunteers listen to audio clips from entertaining movies while undergoing functional MRI scans of their brains. The goal was to find out if, among blind people, the visual cortex is activated consistently for complex auditory tasks. “So we take brain activity in one person, and we correlate it to brain activity in another person. It gives you a way to directly compare how similar the processing of two brains is when they’re listening to a given stimulus. And so that can tell us, for example, whether the visual cortices of different blind people are doing the same thing at the same time.” The result? “You get massive synchrony over something like 65 percent of the occipital lobe, which is a lot of cortical territory.” In other words, in blind participants, most areas of the visual cortex were activated at the same time by the movie audio. But the visual cortices of sighted people didn’t show consistent activation.

What’s more, the similarities became much less pronounced among the blind participants when the movie clips were scrambled and became meaningless. That finding suggests the visual cortex isn’t just acting like a simple sound processor. “And that’s important because it means that this brain region likely went from being a low-level sensory area to behaving like a higher cognitive area, which suggests a very extreme level of reorganization and plasticity.” The study appears in the Journal of Neuroscience.

Further research will investigate other ways in which life experiences may profoundly shape cognitive function, from reading braille to programming computers.

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