Gazzaniga M S
Center for Cognitive Neuroscience, Dartmouth College, Hanover, New Hampshire 03755, USA.
Adv Neurol. 1998;77:181-92; discussion 192-3.
There is a deep belief that we can attain not only a neuroscience of consciousness but a neuroscience of human consciousness. It is as if something terribly new and complex happens as the brain enlarges to its human form. Whatever this is, it triggers our capacity for self-reflection, for ennui, and for lingering moments, I would like to propose a simple, three-step suggestion. First, we should focus on what we mean when we talk about conscious experience. It is merely the awareness we have of our capacities as a species, but not the capacities themselves--only the awareness or feelings we have about them. The brain is clearly not a general purpose computing device but is a collection of circuits devoted to quite specific capacities. This is true for all brains, but what is wonderful about the human brain is that we have untold numbers of these capacities. We have more than the chimp, which has more than the monkey, which has more than the cat, which runs circles around the rat. Because we have so many specialized systems and because they can frequently do things they were not designed to do, it appears our brains have a single, general computing device. But we do not. Thus, step 1 requires that we recognize we are a collection of adaptations and, furthermore, we recognize the distinction between a species' capacities and its feelings about those capacities. Now consider step 2. Can there be any doubt that a rat at the moment of copulation is as sensorially fulfilled as a human? Of course it is. Do you think a cat does not enjoy a good piece of cod? Of course it does. Or, a monkey does not enjoy a spectacular swing? Again, it has to be true. Each species is aware of its special capacities. So, what is human consciousness? It is the very same awareness, save for the fact that we can be aware of so much more, so many wonderful things. A circuit--perhaps a single system or one duplicated over and over again--is associated with each brain capacity. The more systems a brain possesses, the greater the awareness of capacities. Think of the variations in capacity within our own species; they are not unlike the vast differences between species. Years of split-brain research have informed us that the left hemisphere has many more mental capacities than the right one. The left is capable of logical feats that the right hemisphere cannot manage. Although the right has capacities such as facial recognition systems, it is a distant second with problem-solving skills. In short, the right hemisphere's level of awareness is limited. It knows precious little about a lot of things, but the limits to human capacity are everywhere in the population. No one need be offended to realize that just as someone with normal intelligence can understand Ohm's law, others, like yours truly, are clueless about Kepler's laws. I am ignorant about them and will remain so. I am unable to be aware about what they mean for the universe. The circuits that enable me to understand these things are not present in my brain. By emphasizing specialized circuits that arise from natural selection, we see that the brain is not a unified neural net that supports a general problem-solving device. With this being understood, we can concentrate on the possibility that smaller, more manageable circuits produce awareness of a species' capacities. Holding fast to the notion of a unified neural net means we can understand human conscious experience only by figuring out the interactions of billions of neurons. That task is hopeless. My scheme is not. Hence step 3. The very same split-brain research that exposed shocking differences between the two hemispheres also showed that the human left hemisphere has the interpreter. The left brain interpreter's job is to interpret our behavior and our responses, whether cognitive or emotional, to environmental challenges. It constantly establishes a running narrative of our actions, emotions, thoughts, and dreams. It is the glue that keeps our
有一种根深蒂固的信念,即我们不仅能够获得关于意识的神经科学,还能获得关于人类意识的神经科学。仿佛当大脑扩展到人类形态时,会发生某种极其新颖和复杂的事情。不管这是什么,它引发了我们的自我反思能力、倦怠感以及那些挥之不去的时刻,对此我想提出一个简单的三步建议。首先,我们应该关注当我们谈论有意识的体验时我们的意思是什么。它仅仅是我们作为一个物种对自身能力的意识,而不是能力本身——只是我们对这些能力的意识或感受。大脑显然不是一个通用的计算设备,而是由致力于相当特定能力的电路组成的集合。所有的大脑都是如此,但人类大脑的奇妙之处在于我们拥有无数这样的能力。我们比黑猩猩拥有的更多,黑猩猩比猴子拥有的更多,猴子比猫拥有的更多,而猫又比老鼠强得多。因为我们有如此多的专门系统,并且因为它们常常能做一些它们并非被设计来做的事情,所以看起来我们的大脑有一个单一的通用计算设备。但实际上我们没有。因此,第一步要求我们认识到我们是一系列适应性的集合,而且,我们要认识到一个物种的能力与其对这些能力的感受之间的区别。现在考虑第二步。毫无疑问,一只正在交配的老鼠在感官上的满足程度和人类一样吧?当然是。你认为一只猫不喜欢一块美味的鳕鱼吗?当然喜欢。或者,一只猴子不喜欢一次精彩的荡秋千吗?同样,这肯定是真的。每个物种都意识到自己的特殊能力。那么,人类意识是什么呢?它是同样的意识,只是我们能够意识到更多、如此多奇妙的事情。一个电路——也许是一个单一的系统或者一个反复复制的系统——与每一种大脑能力相关联。一个大脑拥有的系统越多,对能力的意识就越强。想想我们自己物种内部能力的差异;它们与不同物种之间的巨大差异并无不同。多年的裂脑研究告诉我们,左半球比右半球拥有更多的心理能力。左半球能够完成右半球无法处理的逻辑壮举。虽然右半球有诸如面部识别系统等能力,但在解决问题的技能方面它远居第二。简而言之,右半球的意识水平是有限的。它对很多事情知之甚少,但人类能力的局限在人群中随处可见。意识到就像一个智力正常的人能理解欧姆定律一样,其他人,比如我自己,对开普勒定律却一无所知,没有人会因此而生气。我对它们一无所知,而且将一直如此。我无法意识到它们对宇宙意味着什么。我大脑中没有能够让我理解这些事情的电路。通过强调自然选择产生的专门电路,我们看到大脑不是一个支持通用问题解决设备的统一神经网络。明白了这一点,我们就可以专注于这样一种可能性,即更小、更易于管理的电路产生对一个物种能力的意识。坚持统一神经网络的概念意味着我们只能通过弄清楚数十亿神经元的相互作用来理解人类有意识的体验。那项任务毫无希望。我的方案并非如此。因此是第三步。揭示两个半球之间惊人差异的同样的裂脑研究也表明,人类左半球有解释器。左脑解释器的工作是解释我们的行为以及我们对环境挑战的反应,无论是认知上的还是情感上的。它不断地为我们的行动、情感、思想和梦想构建一个连贯叙述。它是维系我们的……的粘合剂 (原文此处似乎不完整)