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Thursday, May 13, 2010

Mirror neuron system not responsible for autism

It has been hypothesized that autism results, at least in part, from a defect in the mirror neuron system of the brain. Ilan Dinstein, formerly from New York University, and his colleagues have now shown that this hypothesis is most likely false. Autistic people do not show significant differences in their mirror neuron systems.

Mirror neurons are found in two distinct regions of the brain. As their name implies, they ‘mirror’ or mimic actions performed by others. For example, if I scratch my nose, particular neurons in my brain will fire. If I observe you scratching your nose, those same neurons will fire just as if I were scratching my own nose. Why is this important? It literally allows me to put myself in your place, to feel your pain, as it were. Without mirror neurons, it might be impossible to understand other people’s behavior or intentions.

It had been thought that because autistic people often have difficulty in interpreting the intentions of other people, they might have a defect in their mirror neuron system. Preliminary research has backed this up, though not always consistently. Dinstein and his colleagues decided to look specifically at movement-selective neurons, the neurons that distinguish between thumbs up and thumbs down, for instance. Like other neurons, these neurons adapt to repeated identical stimulation by fading (firing less strongly). The researchers hypothesized that if autistic people have functional mirror neurons, those neurons will display the same degree of adaptation to repeated stimulation as the neurons of their non-autistic cohorts. This is exactly what they found. Functional magnetic resonance imaging (fMRI) studies on both autistic people and non-autistic controls showed the same pattern of fading.

This finding is controversial for a number of reasons, not least because it contradicts some previous data. Dinstein and his colleagues suggest that those studies were inconclusive. Also, this new study only looked at a subgroup of mirror neurons, those responsible for interpreting and mimicking specific motions. There is probably more to mirror neurons than just recognizing actions, and those other functions might still be affected in autistic individuals. Clearly, more work is required in this field.

Watch a video explaining these results here.