Frontier: Mirror neurons may come in different types

by Ben Mauk

November, 2007

Mirror neurons, an intriguing class of brain cells thought to enable us to mimic others’ movements and perhaps learn to speak, may come in three distinct types, which researchers suggest could help explain the brain’s basis for intent and cooperation.

Discovered in monkeys 11 years ago, mirror neurons—brain cells that become active both when relaying signals for carrying out a specific action and when observing that action being performed by others—have now been directly observed in humans, researchers at the meeting said.

In one recent study, Peter Their and colleagues at Tübingen University in Germany observed three distinct classes of these cells in monkeys. Their’s team recorded single-cell activity in mirror neurons while the animals observed and performed actions.

The first neuron class fired only when the action occurred within the monkey’s reaching distance (regardless of whether the action was performed or merely observed by the monkey). The second class fired only when the action was performed in “extrapersonal” space, beyond the monkey’s reach. The third class responded in both cases.

“Mirror neurons are moderated by … where the action takes place,” researcher Antonio Casile said. He went on to speculate, “Maybe they cover three possible cognitive roles. In particular, mirror neurons that respond only to interpersonal space might be for … actions that the monkey can modify.

The neurons that fired when an action was performed outside of the monkey’s reach may stem from “a primitive system for recognizing the actions of others,” Casile added.

Their suggested that the proximity-specific activity might figure into the brain’s understanding of the intentions of others and cooperative behavior.