The cells are a special type of "mirror neurons," which are thought to aid understanding of the actions and intentions of others. Mirror neurons fire both when you do something, like grab a bottle of wine, and when you watch another person do the same thing. Instead of carrying out a step-by-step reasoning process to figure out why a friend is grabbing a bottle of wine, we instantly understand what's going on inside his head because it's going on in our heads too.
Now, researchers have discovered some mirror neurons don't just care about what another individual is doing, they also care about how far away they're doing it, and, more importantly, whether there's potential for interaction.
"This was very surprising for us," said Antonino Casile of the University of Tübingen in Germany, co-author of the research, published in Science Thursday. "The current view about mirror neurons is that they might underlie action understanding. But the distance at which an action is performed plays no role in understanding what the others are doing."
The findings suggest an expanded role for mirror neurons in social interaction. Not only do they facilitate quick comprehension, but they may also help us instantly decide whether to respond and interact. If our friend drops the bottle of wine, we're ready to swoop in before it crashes to the floor. When someone special puckers up, you don't have to think before leaning in for the kiss.
The researchers located mirror neurons in the brains of two monkeys, which fired when the monkeys grabbed a small metal object and when they watched the experimenter do the same. Unexpectedly many of these neurons actually had a preference for where the experimenter was grabbing the object - about a fourth of the cells fired more rapidly when the action took place within arm's reach of the monkey (its "peripersonal" space), while another fourth were more excited when the action was out reach (its "extrapersonal space"). Over a range of distances, the closer the motion was to the monkey, the faster its peripersonal mirror neurons fired; the extrapersonal mirror neurons had the opposite response.
Distance shouldn't make a difference for understanding or imitating a task, or for any of the commonly attributed functions of mirror neurons. However, distance plays a fundamental role in deciding how to respond to behaviors.
"Our brain divides space into at least two major sectors - one in which we can do things, in which we can act, and one in which we can't," explained Marco Iacoboni, who studies the human mirror neuron system at the University of California at Los Angeles. "Our cognition, even fairly complex stuff like empathy, seems grounded in our body."
The researchers also demonstrated that it's not mere distance that affects these neurons, but more specifically, whether there is indeed potential to act. They did the same tests with a clear barrier between the monkey and the experimenter's grabbing, eliminating the possibility of interaction. Even though the monkey never tried to grab the object during any of the experiments, the barrier stopped some peripersonal mirror neurons from firing, even when the grabbing was very close to the monkey. Meanwhile, the extrapersonal mirror neurons stepped in and started firing.
Casile speculates that these mirror neurons are analyzing actions both to understand what others are doing and to decide what one could do in order to interact with them, and that these analyses are happening simultaneously. "We might be deciding whether and how to interact with an action not after understanding it, but rather in parallel," he said.
"Mirror neurons may be very important for social relations," Iacoboni said. "These new findings truly speak to this idea. The neurons may be encoding actions in a way that's essential for cooperating with others, and very important for social interactions."
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