translation.en: To tell if a part of the brain is necessary for a mental function, you need to mess with it and see what happens, and normally we don't get to do that.
translation.zh: 为了确定大脑的一部分是否对于精神功能至关重要， 你需要干扰那一部分的功能，看看会发生什么。 一般我们无法那样做。