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YOUR brain’s ability to identify familiar faces has an interesting quirk. While the right side of the brain recognises other people, it’s the left side that knows you’re you.

Experiments show that our right brain is far better at recognising familiar faces such as friends or celebrities than our left brain. But according to David Turk at Dartmouth College in Hanover, New Hampshire, it hasn’t been clear which brain hemisphere recognises its owner most easily.

To find out, he and his team enlisted the help of a “split-brain” patient, “JW”. His two brain hemispheres can’t communicate because the connections between them have been surgically severed, to combat severe epilepsy. Only the left side of his brain responds to things he sees in the right visual field, and vice versa.

The researchers took a photo of JW and “morphed” it to varying degrees with a photo of one of their team, Michael Gazzaniga, whom JW had known for more than 20 years. Then they showed the original photos and nine intermediate morphs to JW, in his right and left visual fields in turn. By pressing a button, JW had to answer the question: is that me or is that Mike?

It turned out that JW’s right brain had a bias towards identifying morphed faces as Mike, but the left side did the opposite, favouring himself. To make sure the effect wasn’t just something to do with Mike’s face, the team repeated the tests by morphing photos of JW with Bill Clinton, George Bush and someone else JW knew personally. The results were similar to those in the first experiment (Nature Neuroscience, DOI: 10.1038/nn907).

Turk concludes that the left brain is specially geared up to recognise “me” while the right side registers “not me”. The fact that there’s a separate, specialised way of identifying yourself is not surprising, says team member Margaret Funnell, because a distinct sense of self is essential to human intellectual abilities, such as introspection and self-consciousness. “I don’t know how someone could live in a community without that,” she says.