A recent study conducted by researchers at Karolinska Institutet has identified how alpha oscillations, a type of rhythmic brain wave, help the brain distinguish between one's own body and the external environment. The research was published in Nature Communications.
The study involved 106 participants and used a combination of behavioral experiments, EEG brain recordings, non-invasive electrical brain stimulation, and computational modeling. The focus was on understanding how visual and tactile sensory signals are integrated to produce the sense of body ownership—the feeling that one’s body parts belong to oneself.
Researchers utilized the rubber hand illusion to investigate this phenomenon. In this setup, participants saw a rubber hand being touched while their real hand was hidden but also touched in synchrony. Many reported that the rubber hand felt like part of their own body when touches were synchronized; when timing differed, this sensation diminished.
The findings indicated that individuals with faster alpha wave frequencies in the parietal cortex—a region processing sensory information—were more sensitive to slight timing differences between what they saw and felt. This resulted in a sharper distinction between self-related sensations and external ones. Conversely, those with slower alpha frequencies had a broader temporal binding window: their brains tended to merge less synchronous signals as if they occurred together, making it harder to separate self from non-self.
Researchers further tested whether changing alpha frequency could directly affect perception by using electrical stimulation to alter these rhythms. They found that adjusting alpha frequency changed how precisely people experienced body ownership and perceived simultaneity between visual and tactile stimuli. Computational models supported these results by showing that alpha frequency influences the accuracy with which the brain judges sensory signal timing.
"Our findings help explain how the brain solves the challenge of integrating signals from the body to create a coherent sense of self," said Henrik Ehrsson, professor at the Department of Neuroscience at Karolinska Institutet and last author of the study. "This can contribute to the development of better prosthetic limbs and more realistic virtual reality experiences."
The project was carried out in collaboration with Aix-Marseille Université in France and received funding from several organizations including the European Research Council (ERC), Swedish Research Council, VINNOVA, StratNeuro, and A*Midex.
