For most of us, it's not too hard to tell when Mom isn't crazy about the holiday gift we got her. Although she tries to smile, her wrinkled brow confirms that a stuffed lizard was probably the wrong choice. But these facial clues aren't so clear to autistic people, for whom grasping even the obvious emotions of others is like deciphering a complex code. A new study indicates the disparity may lie in brain regions that help us put ourselves in someone else's shoes.
One theory for why the autistic brain works differently than the normal brain is that the mirror neuron system (MNS), which normally helps us understand the actions of others, isn't doing its job. When you see your mother's furrowed brow, neurons in the part of the brain that controls facial muscles fire up, essentially "mirroring" her expression and giving you a clue to what she's feeling.
To see if the MNS is different in autistic people, a team led by Mirella Dapretto, a neuroscientist at the University of California in Los Angeles, asked ten autistic and 10 normal adolescents to imitate angry, fearful, happy, and neutral facial expressions flashed on a computer screen. Meanwhile, the team filmed the kids' impersonations and used functional magnetic resonance imaging to record their brain activity.
The autistic children had no problem imitating the faces, showing that they were getting the same information as the other children, but their MNS was significantly less active. And the more severe the social dysfunction of the autistic child, the weaker the MNS activity, the team reports online 4 December in Nature Neuroscience. Dapretto hypothesizes that without the help of the emotional mirror, the brains of autistic children are forced to come up with alternative--and less effective-- strategies for guessing how others feel, for example by memorizing the emotional significance of different expressions.
"I am very excited by these findings," says Justin Williams, a neuroscientist at the University of Aberdeen Medical School, U.K. Williams, one of the first to propose the MSN explanation for autism in 2001, says the next step is to determine why the autistic brain develops this way.