A new study from Karolinska Institutet, published in Nature Communications, reveals how rhythmic brain waves known as alpha oscillations help us distinguish between our own body and the external world. The findings offer new insights into how the brain integrates sensory signals to create a coherent sense of bodily self.

What makes you feel that your hand is yours? It might seem obvious, but the brain’s ability to tell self from non-self is a complex process.

Using a combination of behavioural experiments, brain recordings (EEG), brain stimulation, and computational modelling with a total of 106 participants, researchers from Karolinska Institutet investigated how the brain combines visual and tactile signals to create the feeling that a body part belongs to oneself – a phenomenon known as the sense of body ownership. Their experiments showed that the frequency of alpha waves in the parietal cortex, the brain region that processes sensory information from the body, determines how precisely we perceive our body as our own.

“We have identified a fundamental brain process that shapes our continuous experience of being embodied,” explains lead author Mariano D’Angelo, researcher at the Department of Neuroscience, Karolinska Institutet. “The findings may provide new insights into psychiatric conditions such as schizophrenia, where the sense of self is disturbed.”

The rubber hand illusion

Participants took part in the rubber hand illusion, a classic method for studying the sense of body ownership. When touches on a visible rubber hand and the participant’s hidden real hand were synchronised, many reported feeling that the rubber hand was part of their body. But when the timing was off, that feeling faded.

The study found that individuals with faster alpha frequencies were more sensitive to timing differences between the seen and felt touches. They noted smaller timing differences, as if their brains operated at higher temporal resolution, resulting in a more precise sense of body ownership.

In contrast, slower alpha frequencies were linked to a broader ‘temporal binding window,’ causing the brain to treat more asynchronous visual and tactile signals as if they occurred together. This reduced temporal precision made it harder to separate self-related sensations from external ones, weakening the distinction between body and world.

Better prostheses and VR experiences

To test whether alpha frequency directly causes these perceptual effects, the researchers used non-invasive electrical brain stimulation to slightly speed up or slow down participants’ alpha waves. The results showed that adjusting the alpha frequency in this way also changed how precisely people experienced body ownership and how precisely they perceived visual and tactile stimuli as simultaneous. Computational models showed that alpha frequency influences how precisely the brain judges the timing of sensory signals, meaning that these brain waves regulate the temporal precision of perception and thereby help shape our sense of bodily self.

“Our findings help explain how the brain solves the challenge of integrating signals from the body to create a coherent sense of self,” says Henrik Ehrsson, professor at the Department of Neuroscience, Karolinska Institutet, and last author of the study. “This can contribute to the development of better prosthetic limbs and more realistic virtual reality experiences.”