Awareness of one’s own body is based on uncertainty and guesses

Researchers at Karolinska Institutet have found that the perception of one's own body is very based on the brain making guesses based on probability theory. It shows a study recently published in the journal eLife.

How we perceive our own body is largely based on probability assessments based on past experiences, in combination with sensory information such as vision and feeling, for example.

You could say that the experience of your own body is a statistical estimate of reality based on sensory information, sensorory uncertainty, and past experiences that can be summed up in the mathematical model explain Henrik Ehrsson, professor at the Department of Neuroscience, Karolinska Institutet.

Why are these results important??

Henrik Ehrsson, Professor at the Department of Neuroscience.
Photo credit: Sören Vilks

The results clarify the computational science functions that control the perception of one's own body. This perception thus arises not only as a result of a "direct" interpretation of signals from vision, touch sense, and joint sensitivity as it says in the textbooks, but rather is based on active guesses that the brain constantly makes based on probability theory and the information that can be extracted from the pattern of the sensor signals, says Henrik Ehrsson.

The experiments were based on the so-called rubber hand illusion where the researchers first made the participants perceive a rubber hand as their own. The illusion was created by synchronizing visual and sensory impressions with one's own hand and rubber hand using a robot and VR glasses.

When we varied the degree of time delay between the visual and sensory impressions in small steps, or made the image in the VR glasses blurry to increase uncertainty, then the illusion changed in a way that can be described by equations and curves: increased delay gave a weaker sense of the rubber hand as its own, while increasing uncertainty (blur) made the illusion stronger, Tells Marie Chancel, co-author of the study.

Marie Chancel, researcher at the Department of Neuroscience, Karolinska Institutet.
Photo credit: Gabriel Wink

With a starting point in the experiments, the researchers identified a statistical explanation model for the brain's estimation of its own body.

Changes in body experience

The next step is to try to understand how the statistical model that controls body perception is implemented by networks in the brain. In a first study, researchers have shown that cerebral cortex activity in the brain lobe follows the Bayesian model well in experiments where they measure brain activity with functional magnetic resonance imaging (Chancel et al 2022 J Neurosci). The researchers also want to investigate how their model can explain changes in body experience in various psychiatric and neurological conditions, such as Schizophrenia and Anorexia.

The study was conducted in collaboration with Dr. Wei Ji Ma, New York University, USA, and has been funded by the Swedish Research Council, Göran Gustafsson's Foundation, European Research Council (grant 787386 SELF-UNITY) and the Wenner-Gren Foundations.

Source/Credit: Karolinska Institutet

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