The Tell-Tale Brain: A Neuroscientist's Quest for What Makes Us Human

Let us turn now to the second cluster of symptoms: sensorimotor. On the sensory side, autistic children may find specific sensory stimuli highly distressing. Certain sounds, for example, can set off a violent temper tantrum. There is also a fear of novelty and change, and an obsessive insistence on sameness, routine, and monotony. The motor symptoms include a to-and-fro rocking of the body (such as we saw with Steven), repetitive hand movements including flapping motions and self-slapping, and sometimes elaborate, repetitive rituals. These sensorimotor symptoms are not quite as definitive or as devastating as the social-emotional ones, but they co-occur so frequently that they must be connected somehow. Our picture of what causes autism would be incomplete if we failed to account for them.

There is one more motor symptom to mention, one that I think holds the key to unraveling the mystery: Many autistic children have difficulty with miming and imitating other people’s actions. This simple observation suggested to me a deficiency in the mirror-neuron system. Much of the remainder of this chapter chronicles my pursuit of this hypothesis and the fruit it has borne so far.

Not surprisingly, there have been dozens of theories of what causes autism. These can be broadly divided into psychological explanations and physiological explanations—the latter emphasizing innate abnormalities in brain wiring or neurochemistry. One ingenious psychological explanation, put forward by Uta Frith of University College of London and Simon Baron-Cohen of Cambridge University, is the notion that children with autism have a deficient theory of other minds. Less credible is the psychodynamic view that blames bad parenting, an idea that is so absurd that I won’t consider it further.

We encountered the term “theory of mind” in passing in the previous chapter in relation to apes. Now let me explain it more fully. It is a technical term that is widely used in the cognitive sciences, from philosophy to primatology to clinical psychology. It refers to your ability to attribute intelligent mental beingness to other people: to understand that your fellow humans behave the way they do because (you assume) they have thoughts, emotions, ideas, and motivations of more or less the same kind as you yourself possess. In other words, even though you cannot actually feel what it is like to be another individual, you use your theory of mind to automatically project intentions, perceptions, and beliefs into the minds of others. In so doing you are able to infer their feelings and intentions and to predict and influence their behavior. Calling it a theory can be a little misleading, since the word “theory” is normally used to refer to an intellectual system of statements and predictions, rather than in this sense, where it refers to an innate, intuitive mental faculty. But that is the term my field uses, so that is the term I will use here. Most people do not appreciate just how complex and, frankly, miraculous it is that they possess a theory of mind. It seems as natural, as immediate, and as simple as looking and seeing. But as we saw in Chapter 2, the ability to see is actually a very complicated process that engages a widespread network of brain regions. Our species’ highly sophisticated theory of mind is one of the most unique and powerful faculties of the human brain.

Our theory-of-mind ability apparently does not rely on our general intelligence—the rational intelligence you use to reason, to draw inferences, to combine facts, and so forth—but on a specialized set of brain mechanisms that evolved to endow us with our equally important degree of social intelligence. The idea that there might be specialized circuitry for social cognition was first suggested by psychologist Nick Humphrey and primatologist David Premack in the 1970s, and it now has a great deal of empirical support. So Frith’s hunch about autism and theory of mind was compelling: Perhaps autistic children’s profound deficits in social interactions stem from their theory-of-mind circuitry being somehow compromised. This idea is undoubtedly on the right track, but if you think about it, saying that autistic children cannot interact socially because they have a deficient theory of mind doesn’t go very far beyond restating the observed symptoms. It’s a good starting point, but what is really needed is to identify brain systems whose known functions match those that are deranged in autism.