Ever wondered how some people can “put themselves into another person’s shoes” and some people cannot? Our ability to empathise with others seems to depend on the action of “mirror neurons” in the brain, according to a new study.

Mirror neurons, known to exist in humans and in macaque monkeys, activate when an action is observed, and also when it is performed. Now new research reveals that there are mirror neurons in humans that fire when sounds are heard. In other words, if you hear the noise of someone eating an apple, some of the same neurons fire as when you eat the apple yourself.

So-called auditory mirror neurons were known only in macaques. To determine if they exist in humans Valeria Gazzola, at the school of behavioural and cognitive neurosciences neuroimaging centre at the University of Groningen, the Netherlands, and colleagues, put 16 volunteers into functional magnetic resonance imaging (fMRI) scanners and observed their brains as they were played different noises.

The volunteers heard noises such as a sheet of paper being torn, or of someone crunching potato chips. Then the same subjects were scanned again, this time whilst tearing a piece of paper, or eating potato chips.


Vicarious crunching

“We combined the data from listening and execution and looked to see if the activity in the brain overlaps,” says Gazzola’s colleague Christian Keysers, also at the University of Groningen. Sure enough, it did overlap. Motor neurons associated with mouth actions (crunching) and hand actions (ripping) were activated in both cases.

The overlap occurred in areas of the brain such as the bilateral temporal gyrus and the superior temporal sulcus.

“The mirror system is a particular form of Pavlovian association,” says Keysers, referring to the classic behavioural experiments where dogs were trained to associate food with the noise of a bell. “Each time you crunch a potato chip you hear yourself crunching the chip, and now when you hear someone else crunching it activates your own action neurons.”

Spectrum of difference

The phenomenon has been exploited by advertisers for years – think of the Coca-cola commercials comprising of just the noise of a bottle of Coke being opened, the fizz of the drink and the sound of the drinking. And intriguingly, subjects in the study who scored higher in empathy tests also showed higher levels of mirror neuron activation.

Differences in empathy scores and mirror neuron activity have been observed between autistic and non-autistic people, says Keysers, but this is the first time a spectrum of difference has been found in non-autistic people. “How empathetic we are seems to be related to how strongly our mirror neuron system is activated,” he says.

“It’s exciting because we can start to look at the diversity of experiences of other people. Some people see others through themselves, and some are more objective about it.”

Journal reference: Current Biology (vol 16, p 1824)