Mirror neurons seen behaving normally in autism

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Mirror neurons seen behaving normally in autism

18:37 12 May 2010 by Ewen Callaway

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People with autism seem to have normal " mirror " neurons after all. A popular

theory has it that these neurons – brain cells that fire both when you perform

an action and when you watch someone else doing the same thing – don't work

properly in people with autism. Now it looks as though that isn't so.

The idea was that malfunctioning mirror neurons underlie the difficulties that

people with autism have in interpreting the intentions of others. It seemed to

be backed up by studies in which the brain activity of normal and autistic

people was measured while they watched and performed simple actions, such as

hand movements. In many, but not all of these studies, brain areas rich with

mirror neurons proved less active in the people with autism.

But Ilan Dinstein, a neuroscientist at the Weizmann Institute in Rehovot,

Israel, says other differences besides faulty mirror neurons could explain these

results. For instance, if it turns out that people with autism imitate or detect

hand movements more slowly than others, brain scans could mistake this delay for

dysfunction in mirror neurons, he says.

No mirror dysfunction

So Dinstein and his colleagues at New York University turned to a more sensitive

test for mirror neuron activity that he and others discovered recently in

healthy people. Like brain cells that respond to sounds and smells, mirror

neurons fire a little more weakly in response to repeated activation by an

exactly repeated movement.

Dinstein's team asked 13 autistic adults and 10 controls to watch or perform a

series of hand signals – thumbs up and miming holding a gun, for instance –

while in a functional MRI scanner. In some trials they performed or watched the

same hand movement over and over again, while in others they performed or

watched successions of different signals.

Brain areas linked to the mirror neuron system – parts of the premotor and the

parietal cortices – lit up in both groups, whether they watched or performed a

hand-movement. What's more, the mirror neuron activity quieted when both groups

observed or performed the same signal over and over, but not when they performed

a succession of different movements, suggesting that the system was working

normally in people with autism. " That argues against a mirror system dysfunction

in autism, " says Dinstein.

However, Marco Iacoboni, a neuroscientist at the University of California, Los

Angeles, one of the first scientists to suggest that mirror neurons were

dysfunctional in autism, says that 13 autistic and 10 normal subjects are too

few to draw any conclusion about brain differences between these groups.

Noisy brains

Iacoboni's UCLA colleague Mirella Dapretto adds that even if the findings do

hold in larger groups of people, they still don't rule out the idea that mirror

neurons could be behaving abnormally in autism. She has previously argued that

the more extreme a person's autism symptoms, the more problems they have in

their mirror neuron system.

Dinstein stands by his team's conclusions. The number of participants he

examined is typical for brain imaging studies, he says, and their autistic

participants, though high-functioning, possessed the most extreme form of autism

spectrum disorder, not milder forms such as Asperger's syndrome.

He supports a different theory for autism: that it is the product of " noisy

brain networks " that don't communicate as predictably as those in normal people.

He says his latest study offers support for this, as his team noticed more

variability in the brain activity of people with autism, compared with controls.

He plans to probe this theory by searching for noise in other brain areas in

people with autism.

Journal reference: Neuron, DOI: 10.1016/j.neuron.2010.03.034