When will “you” end and the outside world begin?

This may seem like a strange question, but obvious answerBut the brain has to work incredibly hard to determine those boundaries. Scientists have now linked certain brain waves in certain parts of the brain to a sense of ownership of one’s body.

In a series of new experiments, researchers in Sweden and France put 106 participants through so-called “experiments.” rubber hand illusionmonitor and stimulate brain activity and see what effect it has.

Related: Octopuses fall for the classic fake arm trick – just like us

This classic illusion involves hiding one of the participant’s hands from view and replacing it with a rubber hand. Repeated touching of both the real and fake hands at the same time can evoke the eerie feeling that the rubber hand is part of the person’s body.

Testing included EEG in one experiment (EEG test) Measurements of brain activity reveal that the feeling of ownership of one’s body appears to arise from the frequency of alpha waves within the body. parietal cortexThe brain area responsible for body mapping, Processing sensory input and build a sense of self.

“We have identified fundamental brain processes that shape the ongoing experience of being embodied.” say Lead author Mariano D’Angelo is a neuroscientist at the Karolinska Institute in Sweden.

“The results of this study may provide new insights into mental illnesses such as: schizophreniawhere self-consciousness is disturbed. ”

In the first batch of experiments, participants tapped the index fingers of their real and fake hands with a robotic arm either at exactly the same time or with a delay of up to 500 ms between each tap.

As expected, participants reported a stronger sense that the fake hand was part of their body when the taps were synchronous, but that feeling gradually weakened as the gap between what they felt and what they saw widened.

EEG measurements from the second experiment added further details to the story. frequency of alpha waves Changes in parietal cortex appear to correlate with how well participants can detect time delays between taps.

People with fast alpha waves seemed to eliminate the possibility of a fake hand even if the taps were far apart, whereas people with slow alpha waves were more likely to perceive a fake hand even if the taps were far apart.

Finally, the researchers investigated whether these brainwave frequencies actually control the sense of body ownership, or perhaps both are an influence of some other factor.

A third group of participants used a non-invasive technique called . Transcranial AC stimulation Speeding up or slowing down a person’s alpha wave frequency. And sure enough, this seemed to correlate with the feel of the fake hand.

Increasing the speed of your alpha waves gives you a greater sense of ownership over your body and makes you more sensitive to small timing discrepancies. Slowing the waves had the opposite effect, making it difficult for people to tell the difference between their bodies and the outside world.

“Our findings help explain how the brain meets the challenge of integrating signals from the body to create a coherent sense of self.” say Henrik Ehrsson, neuroscientist at Karolinska University.

Researchers say this discovery could lead to new understanding and treatments for conditions in which the brain’s body map is distorted, such as: schizophrenia Or the feeling ofphantom limbWhat amputees experience.

Also, more realistic prosthetics and even virtual reality tools.

The study was published in the journal nature communications.