A study from Karolinska Institutet, published in ‘Nature Communications’, explains how rhythmic brain activity known as ‘alpha oscillations’ helps the brain separate the body from the outside world. The research provides new insight into how the brain combines information from different senses to maintain a stable feeling of bodily self.
Feeling that your hand belongs to you may seem automatic, but the brain must constantly evaluate sensory information to make that judgment. Distinguishing what is part of the self and what is not is a demanding task that relies on precise brain processes.
Combining sight and touch
Researchers at Karolinska Institutet studied this process using behavioural experiments, brain recordings (EEG), brain stimulation, and computational modeling. A total of 106 participants took part. The team examined how visual and tactile signals are merged to create the experience that a body part belongs to oneself, a process known as the sense of body ownership.
Their findings showed that the speed of alpha waves in the parietal cortex plays a critical role. This region processes sensory information from the body, and the frequency of its alpha activity determines how accurately people perceive their own body as belonging to them.
“We have identified a fundamental brain process that shapes our continuous experience of being embodied,” explains lead author and researcher at the Department of Neuroscience, Karolinska Institutet Mariano D’Angelo. “The findings may provide new insights into psychiatric conditions such as schizophrenia, where the sense of self is disturbed.”
What the rubber hand
illusion shows
To explore body ownership more directly, participants completed the rubber hand illusion, a widely used experimental setup. In this task, a fake hand is placed in view while the real hand is hidden. When both hands are touched at the same time, many participants begin to feel as though the rubber hand is part of their own body. When the timing between touches does not match, that illusion weakens.
The study found that people with faster alpha wave frequencies were better at detecting small timing differences between what they saw and what they felt. Their brains processed sensory information with greater timing accuracy, leading to a sharper and more reliable sense of body ownership.
When brain timing
becomes less precise
Participants with slower alpha frequencies showed a different pattern. Their brains had a wider ‘temporal binding window,’ meaning visual and tactile signals were more likely to be treated as happening together even when they were slightly out of sync.
This reduced timing precision made it harder to clearly distinguish self related sensations from external input, weakening the boundary between the body and the surrounding environment.
Implications for prosthetics
and virtual reality
To determine whether alpha wave frequency directly influences these effects, the researchers used non-invasive electrical brain stimulation to gently increase or decrease the speed of participants’ alpha rhythms. Changing the frequency altered how precisely participants experienced body ownership and how accurately they judged whether visual and tactile signals occurred at the same time.
Computational models supported these results, showing that alpha frequency affects how precisely the brain evaluates the timing of sensory information. By regulating this timing, alpha oscillations help shape perception and contribute to the experience of having a body.
“Our findings help explain how the brain solves the challenge of integrating signals from the body to create a coherent sense of self,” says professor at the Department of Neuroscience, Karolinska Institutet, and senior author of the study Henrik Ehrsson. “This can contribute to the development of better prosthetic limbs and more realistic virtual reality experiences.”
(Science Daily)
