In two different experiments, they delivered histamine – the chemical the body produces when it is having an allergic reaction – to the arms of healthy volunteers while they were under the illusion that their real arm had been replaced by a rubber one.
They compared the size of the allergic response on the arm that had been ‘replaced’ to the response on the other arm and then to the response on both arms during a control condition that had no illusion.
They found that during the illusion, the response to histamine was bigger on the arm that had been replaced by the rubber one.
Lead scientist Professor Lorimer Moseley said: “This remarkable effect of an histamine response confined to one arm and dependent on the illusion might be a kind of neglect involving the immune system’’.
The finding builds on another discovery by Professor Moseley’s team that the disowned hand goes colder during the “rubber hand illusion’’.
“These findings strengthen the argument that the brain exerts some kind of control over specific body parts according to how strongly we own them,’’ he said Professor Moseley.
The findings have implications for a range of conditions in which people describe a loss of their sense of ownership over a body part or limb. The histamine study was published in Current Biology on Dec 6.