Participants took part in an experiment called the rubber hand illusion in Henrik Ehrsson's lab at Karolinska Institutet.
Photo Credit: Martin Stenmark
Scientific Frontline: "At a Glance" Summary
- Main Discovery: Alpha oscillations in the parietal cortex function as the primary neural mechanism for distinguishing one’s own body from the external environment by regulating the integration of sensory signals.
- Methodology: Researchers combined the "rubber hand illusion" with EEG recordings, computational modeling, and non-invasive electrical brain stimulation across 106 participants to causally link brain wave speeds to perception.
- Mechanism: The specific frequency of alpha waves determines the brain's "temporal binding window"; faster oscillations create a higher temporal resolution, allowing for a precise rejection of asynchronous (non-self) stimuli.
- Key Correlation: Individuals with naturally slower alpha frequencies demonstrated a broader integration window, causing the brain to erroneously merge mismatched visual and tactile inputs into a false sense of body ownership.
- Significance: These findings establish a physiological target for treating self-disorders in conditions like schizophrenia and provide a blueprint for improving the "embodiment" of prosthetic limbs and virtual reality systems.
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.
“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 synchronized, 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 and last author of the study. “This can contribute to the development of better prosthetic limbs and more realistic virtual reality experiences.”
Funding: European Research Council (ERC), the Swedish Research Council, VINNOVA, StratNeuro and A*Midex.
Disclaimer: The researchers declare that there are no conflicts of interest.
Additional information: The study was a collaboration between Karolinska Institutet in Sweden and Aix-Marseille Université in France.
Published in journal: Nature Communications
Authors: Mariano D’Angelo, Renzo C. Lanfranco, Marie Chancel, and H. Henrik Ehrsson
Source/Credit: Karolinska Institutet | Felicia Lindberg
Reference Number: ns011226_02
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