BRAIN cells that may underlie our ability to empathise with others have been detected directly in people for the first time.
Monkey brains have been shown to contain so-called “mirror” neurons, which fire both when the animal performs an action and when it observes others performing that action. Until now, the only evidence that our brains contain similar neurons has been indirect, derived from functional MRI scans.
Now Roy Mukamel at the University of California, Los Angeles, and colleagues have observed mirror neurons directly in humans. They used electrodes to record brain activity in the medial frontal and temporal cortices of 21 people awaiting surgery to treat epilepsy, while they made – or observed others making – grasping actions and facial expressions.
The majority of these neurons responded only to the observation or execution of an action, but 8 per cent of the cells responded to both (Current Biology, DOI: 10.1016/j.cub.2010.02.045). These areas of the brain are involved in planning and controlling actions, abstract thinking and memory.
Mirror neurons were thought to exist primarily in regions of the brain involved in performing actions, so their presence in other regions suggests that this is not their only role. Other studies have found that people who appear to have more active mirror neurons also tend to be more empathetic. Marco Iacoboni, another member of the team and also at UCLA, says his team’s results suggest that human mirror neurons provide “a rich reflection of the actions of others”.
Alfonso Caramazza at Harvard University rejects this idea. “We should abandon the notion that these neurons are allowing us to mirror another’s actions internally,” he says.
Both agree that the ultimate test would be to block mirror neurons in animals and see if they no longer comprehend the actions of others. There is no easy way to do this yet, says Mukamel, but optogenetics – the ability to manipulate or block neural activity using light – may one day provide a solution.