When a person looks down at his own body, he knows it is his own, but why? By taking advantage of a body-swap illusion, researchers have captured the brain regions involved in one of the most fundamental aspects of self-awareness: how we recognize our bodies as our own, distinct from others and from the outside world.

That self-perception is traced to specialized multisensory neurons in various parts of the brain that integrate different sensory inputs across all body parts into a unified view of the body.

The findings may have important medical and industrial applications, the researchers say.

“When we look down at our body, we immediately experience that it belongs to us,” said Valeria Petkova of Karolinska Institutet in Sweden, in a press release. “We do not experience our body as a set of fragmented parts, but rather as a single entity. Our study is the first to tackle the important question of how we come to have the unitary experience of owning an entire body.”

Earlier studies showed that the integration of visual, tactile and proprioceptive information (the sense of the relative position of body parts) in multisensory areas constitutes a mechanism for the self-attribution of single limbs, the researchers explained. But how ownership of individual body parts translates into the experience of owning a whole body remained a mystery.

In the new study, the researchers used a body-swap illusion, in which people experienced a mannequin to be their own, in combination with functional magnetic resonance imaging. Participants observed touching of the mannequin’s body from the point of view of the mannequin’s head while feeling identical synchronous touches on their own body, which they could not see.

Those studies revealed a tight coupling between the experience of full-body ownership and neural responses in brain regions known to represent multisensory processing nodes in the primate brain, specifically the bilateral ventral premotor and left intraparietal cortices and the left putamen.

Activation in those multisensory areas was stronger when the stimulated body part was attached to a body as compared with when it was detached, the researchers reported, evidence that the integrity between body segments facilitates ownership of the parts.

“Our results suggest that the integration of visual, tactile and proprioceptive information in body-part-centered reference frames represents a basic neural mechanism underlying the feeling of ownership of entire bodies,” the researchers wrote. The finding generalizes existing models of limb ownership to the case of the entire body.

“From Part- to Whole-Body Ownership in the Multisensory Brain” was reported online on June 16 in Current Biology, a Cell Press publication.

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