Mirror neurons continue to light up neuroscientists’ imaginations, as several new studies show that the nerve cells respond to more than just visual stimuli.
In multiple reports published in the Sept. 19 issue of Current Biology, neuroscientists provide evidence that mirror neurons are multimodal—they are activated by not just by watching actions, but also by hearing and reading about them.
An effort led by Lisa Lisa Aziz-Zadeh, a neuroscientist at the University of Southern California, found that the brain’s premotor cortex shows the same activity when subjects observe an action as when they read words describing it.
“The mirror areas that responded most to observation of mouth actions also responded most to reading sentences about mouth actions,” Aziz-Zadeh said. “This indicates that in addition to execution, action observation, and the sounds of actions, these neurons may also be activated by abstract representations of actions, namely language.”
Until now, researchers had only speculated that mirror neurons might be important for language, she added.
Aziz-Zadeh’s study was co-authored by Giacomo Rizzolatti of the University of Parma in Italy, who, in 1996, accidentally discovered the intriguing subset of neurons, which are located in the brain’s premotor cortex. Rizzolatti found that these cells in the brains of macaque monkeys fire not only when the monkeys actually performed an action, but also when they watched another monkey perform it.
For the recent study, Aziz-Zadeh and Rizzolatti’s team located mirror neurons in human subjects using functional MRI, and then compared which cells’ activated when the subjects observed an action and which responded when subjects read about the action. They found that reading about hand movements activated the same mirror neurons that making the movements did.
A second study co-authored by Aziz-Zadeh and led by Valeria Gazzola and Christian Keysers, cognitive scientists at the University of Groningen in The Netherlands, found that mirror neurons also respond to noise. For instance, the mirror neurons that fire when someone eats a chip also fire when he simply hears someone else eat the snack.
Simone Schütz-Bosbach, a neuroscientist at the University College London, said that research on mirror neurons sheds new light on the relationship between sensing and doing.
“Research in the last few years seems to suggest that perception and action are tightly linked rather than separated,” she said.
Her own study on the role that mirror neurons play in differentiating self from other—which also appears in Current Biology issue—echoes what some neuroscientists have inferred: A network of mirror neurons plays a role in humans’ capacity to learn through imitation, use semantics in language, and feel empathy.
“Understanding others’ actions is a key function in social communication,” Schütz-Bosbach said.
Re-enactment through mirror neurons, she said, “probably helps us to understand what another person is doing and why, and most importantly, what the person will be doing next.”
Originally published September 20, 2006