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

ANDREW WHITTEN’S GROUP in Scotland made this proposal at about the same time ours did, but the first experimental evidence for it came from our lab working in collaboration with researchers Eric Altschuler and Jaime Pineda here at UC San Diego. We needed a way to eavesdrop on mirror-neuron activity noninvasively, without opening the children’s skulls and inserting electrodes. Fortunately, we found there was an easy way to do this using EEG (electroencephalography), which uses a grid of electrodes placed on the scalp to pick up brain waves. Long before CT scans and MRIs, EEG was the very first brain-imaging technology invented by humans. It was pioneered in the early twentieth century, and has been in clinical use since the 1940s. As the brain hums along in various states—awake, asleep, alert, drowsy, daydreaming, focused, and so on—it generates tell-tale patterns of electrical brain waves at different frequencies. It had been known for over half a century that, as mentioned in Chapter 4, one particular brain wave, the mu wave, is suppressed anytime a person makes a volitional movement, even a simple movement like opening and closing the fingers. It was subsequently discovered that mu-wave suppression also occurs when a person watches another person performing the same movement. We therefore suggested that mu-wave suppression might provide a simple, inexpensive, and noninvasive probe for monitoring mirror-neuron activity.

We ran a pilot experiment with a medium-functioning autistic child, Justin, to see if it would work. (Very young low-functioning children did not participate in this pilot study as we wanted to confirm that any difference between normal and autistic mirror-neuron activity that we found was not due to problems in attention, understanding instructions, or a general effect of mental retardation.) Justin had been referred to us by a local support group created to promote the welfare of local children with autism. Like Steven, he displayed many of the characteristic symptoms of autism but was able to follow simple instructions such as “look at the screen” and was not reluctant to have electrodes placed on his scalp.

As in normal children, Justin exhibited robust a mu wave while he sat around idly, and the mu wave was suppressed whenever we asked him to make simple voluntary movements. But remarkably, when he watched someone else perform the action, the suppression did not occur as it ought to. This observation provided a striking vindication of our hypothesis. We concluded that the child’s motor-command system was intact—he could, after all, open doors, eat potato chips, draw pictures, climb stairs, and so on—but his mirror-neuron system was deficient. We presented this single-subject case study at the 2000 annual meeting of the Society for Neuroscience, and we followed it up with ten additional children in 2004. Our results were identical. This observation has since received extensive confirmation over the years from many different groups, using a variety of techniques.²

For example, a group of researchers led by Riitta Hari at the Aalto University of Science and Technology corroborated our conjecture using MEG (magnetoencephalography), which is to EEG what jets are to biplanes. More recently, Michele Villalobos and her colleagues at San Diego State University used fMRI to show a reduction in functional connectivity between the visual cortex and the prefrontal mirror-neuron region in autistic patients.