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

Many brain-imaging studies have been conducted on children with autism, some pioneered by Eric Courchesne. It has been noted, for example, that children with autism have larger brains with enlarged ventricles (cavities in the brain). The same group of researchers has also noted striking changes in the cerebellum. These are intriguing observations that will surely have to be accounted for when we have a clearer understanding of autism. But they do not explain the symptoms that characterize the disorder. In children with damage to the cerebellum due to other organic diseases, one sees very characteristic symptoms, such as intention tremor (when the patient attempts to touch his nose, the hand begins to oscillate wildly), nystagmus (jerky eye movements), and ataxia (swaggering gait). None of these symptoms are typical of autism. Conversely, symptoms typical of autism (such as lack of empathy and social skills) are never seen in cerebellar disease. One reason for this might be that the cerebellar changes observed in autistic children may be the unrelated side effects of abnormal genes whose other effects are the true causes of autism. If so, what might these other effects be? What’s needed, if we wish to explain autism, is candidate neural structures in the brain whose specific functions precisely match the particular symptoms that are unique to autism.

The clue comes from mirror neurons. In the late 1990s it occurred to my colleagues and me that these neurons provided precisely the candidate neural mechanism we were looking for. You can refer back to the previous chapter if you want a refresher, but suffice it to say, the discovery of mirror neurons was significant because they are essentially a network of mind-reading cells within the brain. They provided the missing physiological basis for certain high-level abilities that had long been challenging for neuroscientists to explain. We were struck by the fact that it is precisely these presumed functions of mirror neurons—such as empathy, intention-reading, mimicry, pretend play, and language learning—that are dysfunctional in autism.¹ (All of these activities require adopting the other’s point of view—even if the other is imaginary—as in pretend play or enjoying action figures.) You can make two columns side by side, one for the known characteristics of mirror neurons and one for the clinical symptoms of autism, and there is an almost precise match. It seemed reasonable, therefore, to suggest that the main cause of autism is a dysfunctional mirror-neuron system. The hypothesis has the advantage of explaining many seemingly unrelated symptoms in terms of a single cause.

It might seem quixotic to suppose that there could be a single cause behind such a complex disorder, but we have to bear in mind that multiple effects do not necessarily imply multiple causes. Consider diabetes. Its manifestations are numerous and varied: polyuria (excessive urination), polydypsia (incessant thirst), polyphagia (increased appetite), weight loss, kidney disorders, ocular changes, nerve damage, gangrene, plus quite a few others. But underlying this miscellany is something relatively simple: either insulin deficiency or fewer insulin receptors on cell surfaces. Of course the disease is not simple at all. There are a lot of complex ins and outs; there are numerous environmental, genetic, and behavioral effects in play. But in the big picture, it comes down to insulin or insulin receptors. Analogously, our suggestion was that in the big picture the main cause of autism is a disturbed mirror-neuron system.