If you’ve ever wondered where “you” end and the world begins, new research conducted by scientists in Sweden and France says that your sense of owning your body depends on a rhythmic set of brain waves that can be adjusted.
In the study, which was published in Nature Communications, 106 participants were subjected to the rubber hand illusion, an old-school psychological parlor trick that makes the brain freak out a little. One of a participant’s real hands was hidden from view, replaced with a fake rubber hand. Both the real and the fake hands were tapped at the same time, with a lot of the participants claiming to “feel” the tap on the rubber hand, as if it belonged to them.
Using EEG scans, the researchers found that this sensation tracked closely with alpha brain waves in the parietal cortex, the region responsible for mapping the body and decoding sensory information. It was the speed of the waves that mattered most. Participants with faster alpha waves were quick to notice even slight delays between what they saw and what they felt, making them less likely to think the fake hand was their own.
To test whether these waves were actually driving the illusion, researchers used transcranial alternating current stimulation to speed up or slow down alpha wave activity. They found that by making simple external adjustments, they could affect the speed of these alpha waves. Faster waves sharpened our concept of body boundaries, while slower waves loosened them, opening people up to accept a fake rubber hand as a part of themselves despite all evidence to the contrary.
All this is helping explain how the brain distinguishes the body it’s in from literally everything else, a problem most people never have to deal with unless they have a psychiatric condition like schizophrenia, where one’s sense of self can fragment, or if someone’s physical self has been literally fragmented, as with an amputee experiencing phantom limb syndrome.
Altogether, the research could help people with prosthetics, or it could help the development of virtual reality systems — anything where the brain might need a little convincing that something artificial is part of the physical body.
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