Understanding the phenomenon of mirror neurons could benefit stroke victims, amputees and autistic children.
Mirror neurons are all about connections—between regions of the brain, between thought and action, between one person and another. And if research so far has focused on understanding those links at a basic cellular level, clinicians are experimenting with practical applications in three areas.
Late last year, Navy Commander Jack Tsao, associate professor of neurology at the Uniformed Services University of the Health Sciences in Bethesda, published the results of the first controlled trial of therapy employing mirrors to treat phantom-limb pain, which occurs in almost every amputee and may be unrelentingly severe. According to one theory, the pain is caused by a mismatch in signals from different brain regions that creates the sensation that a missing limb still exists and is fixed in an uncomfortable position. In the trial of 22 people who had lost one foot, those in one group viewed the reflected image of their intact foot as they tried to move the amputated foot that wasn’t there. Soldiers in other groups attempted to move both the intact foot and the phantom foot while looking at a sheet-covered mirror or while closing their eyes and visualizing their missing foot. There was no improvement in these groups. But all subjects who used the mirror had decreased pain, including 70% who were completely cured of pain; the therapy is now standard care at Walter Reed Army Medical Center in Washington, D.C.
Many classic traits of this disorder—deficits in empathy, difficulty imitating others’ actions and poor language development—seem to suggest malfunctioning mirror neurons, and some studies in children with autism have shown reduced activity in areas of the brain thought to contain mirror neurons. One promising therapy, being explored by Jaime Pineda, professor of cognitive science at the University of California, San Diego, involves electrical activity in the sensorimotor cortex, called the mu rhythm, which can serve as an index of mirror neuron activity. Although the mu rhythm is normally suppressed when someone observes or makes a movement as neurons fire randomly relative to one another, the oscillation of this wave is strongest when you are idle and neurons are in a synchronous firing pattern. In autistic children that may not happen. Pineda has been using video games to train autistic children to change their mu rhythms. To move a car around a track or fire lasers at asteroids, the youngsters must enhance that signal—and subsequently engage the mirror neuron system.
It seems to be working. “We think the mirror neurons are firing when they weren’t firing before,” Pineda says. And parents and teachers have noted improvements in the kids’ attention spans and interactions with others.
Mentally mimicking movements or speech may help people who have had a stroke recover speech or the use of impaired limbs, says Steven Small, professor of neurology and psychology at the University of Chicago. Last year, with European researchers, Small published a pilot study of eight stroke patients who showed marked improvement in the use of their arms after four weeks of repeatedly watching videos of an actor moving his arms, then attempting to make the same movements themselves. The subjects also showed increased activation of putative mirror neuron areas. “We may be strengthening existing connections among visuo-motor regions, which may contain mirror neurons, or teaching them to bypass damaged connections,” Small says.