Muscling in on body ownership

The mystery of how the brain develops the sense of ownership that recognises our body belongs to us is a step closer to being solved.

Australian researchers have shown that along with the sense of touch and vision, signalling receptors in the muscles and joints also play a critical role.

The findings, published recently in the Journal of Physiology, will help in designing treatments for disorders of body ownership that can occur with conditions such as stroke, epilepsy and alien hand syndrome, a neurological disorder where a person’s hand appears to take on a mind of its own.

Lead researcher, Dr Lee Walsh, of Neuroscience Research Australia, told DPS eNews that we instinctively know our body parts “belong” to us, but how the brain develops “that map of what belongs to it” is still unknown.

“How do I know my hand is mine and not yours, and that the telephone is not a part of my body?” Dr Walsh asks.

Previous research shows people can be deluded into claiming ownership of an artificial hand.

This is done by simultaneously stroking the subject’s hidden hand and a visible artificial rubber hand.

“Once the illusion of ownership of the hand is established, subjects have physiological responses to threats made against the rubber hand,” Dr Walsh says.

However, in this study the team was interested to see if other sensory channels could also be important in developing body ownership.

“We can use vision to see parts of the body, but we can also see other bodies, so vision alone cannot differentiate foreign body parts from those we own,” Dr Walsh says.

“Muscle receptors can only signal things that are happening to the body so it would seem to be an ideal candidate to signal ownership,” he says.

To test this theory, the team induced an illusion of ownership over a plastic index finger.

Dr Walsh says the finger was used because it is “feasible to block the sense of touch with local anaesthetic”.

The team found the sense of ownership still occurred when participants’ fingers were anaesthetised.

According to Dr Walsh, the results show that visual-tactile cues are not critical in establishing body ownership. Instead muscle-related signals coupled with vision are sufficient for the brain to recognise ownership.

“The results clearly show that muscle receptors contribute to the sense of body ownership,” Dr Walsh says.

There is hope the research will benefit stroke patients in regaining ownership of their body.

“Some stroke patients can develop the feeling that their affected hand or arm no longer belongs to them. This makes rehabilitation and recovery difficult because they disregard the hand and do not use it,” Dr Walsh says.

“Once we understand body ownership better we can look at it in a stroke patient and see what is different between them and healthy people.”

This is the first study to show that the brain uses information from muscles to tell us what our body is and is not.

“This is fundamental to identifying how the brain and body interact to give us a sense of self,” Dr Walsh says.

What are your thoughts on this latest study? Leave a comment in the box below.