Mirror cells' fading spark: empathy-related neurons may turn off in autism.

The social detachment and isolation that characterize autism may stem, at least in part, from a breakdown of brain cells that have been implicated in people's ability to imitate others and to read their thoughts and feelings.

A new brain-imaging investigation tested high-functioning children with autism--kids who score in the normal range on intelligence tests and display only mild-to-moderate social difficulties. As these youngsters view and imitate facial expressions, brain cells called mirror neurons show meager activity, say neuroscientist Mirella Dapretto of the University of California, Los Angeles School of Medicine and her colleagues. Children free of developmental problems exhibit robust responses by these neurons during the same tasks.

"A dysfunctional mirror-neuron system [in autism] could account for both a lack of social motivation and deficits in understanding others' intentions and emotions," Dapretto says.

Mirror neurons, first reported in 1996, respond comparably whether an individual performs a particular action or watches someone else carry it out (SN: 5/24/03, p. 330). Studies since then have suggested that these neurons, which coordinate imitation, participate in a network in the brain's outer layer, or cortex. Collaboration between this network and emotion-regulating parts of the brain fosters empathy, the discernment of others' thoughts and feelings, the UCLA researchers propose.

Dapretto's team used a functional magnetic resonance imaging scanner to measure blood flow in the brains of 10 high-functioning children with autism and 10 neurologically healthy children. Participants ranged in age from 10 to 14 years. The scientists determined brain-cell activity by measuring blood flow.

Each child underwent brain scanning as he or she observed a series of 80 photographs of different faces and then went through the series again to imitate the facial expression in each photo. Expressions conveyed anger, fear, happiness, sadness, or neutrality.

Children in both groups maintained good focus on the photos during the tasks and successfully imitated most facial expressions.

However, during the tasks, kids with autism displayed less blood flow in a key part of the mirror-neuron system than the other youngsters did. Autistic children with the worst social skills exhibited the smallest responses.

Dapretto's group proposes that the youngsters with autism intently scrutinized the details of each face photo in order to imitate what they saw because they were unable to discern the meaning of a facial expression and then use empathy to match it. Brain areas that control visual and motor attention showed unusually intense activity while these children observed and imitated facial expressions, the researchers note.

Their report appears in the January Nature Neuroscience.

Yale University neuroscientist Robert T. Schultz calls the new study a valuable addition to evidence linking autism to scant activity in brain areas governing perception and language.

Autistic kids' striking lack of interest in social pursuits still eludes explanation, he adds. "These children have an insensitivity to social rewards that alters their brain development" Schultz remarks. "We don't know why."