Illusion of three hands can help stroke patients

LONDON - Scientists have created the illusion of having three hands - and made it so realistic that study subjects broke into a sweat when their extra limb was threatened with a knife.

The bizarre insight into how the brain can be fooled may speed the development of life-like prosthetic limbs for stroke patients and others who have lost the use of their own arms.

To create the illusion, Swedish scientists set up an experiment in which a person sat at a table and had a skin-toned rubber artificial arm placed next to their right arm, the journal Public Library of Science ONE reports.

Both their real arm and the artificial one were covered with a cloth up to the shoulder, leaving only the two right hands in clear sight, according to the Daily Mail.

The researchers then used small brushes to tickle the real hand and the rubber hand at the same time and in exactly the same spot and the men in women taking part were asked how they felt.

Surprisingly, many said they felt as if they had two right hands.

“A conflict arises in the brain concerning which of the right hands belongs to the participant’s body,” said neuroscience researcher Arvid Guterstam, from the Karolinska Institute, Sweden.

To prove that the rubber arm was experienced as real, the scientists lunged at the hands with a kitchen knife while measuring levels of sweating from the palm.

Proving that the brain was truly tricked, the volunteers sweated almost as much when the rubber hand was under threat as when their real hand was.

But the brain is not too easily fooled. Placing the rubber hand on the opposite side of the table or replacing it with a rubber foot did not pass muster. The research could be used to create more lifelike prosthetic limbs.