Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, C72
Do muscle afferents contribute to the sense of body ownership?
S. Gandevia1,2, L. D. Walsh1,2, G. Moseley1, J. L. Taylor1,2
1. Neuroscience Research Australia, Randwick, New South Wales, Australia. 2. University of New South Wales, Randwick, Sydney, New South Wales, Australia.
The sense of body ownership, a sense of which things ‘belong’ to our body, is presumably generated from sensory information. Both touch and proprioception seem ideal for this as they only signal events that occur on or within the body. The sense of body ownership can be manipulated using tactile stimuli to induce an illusion of ownership over a rubber hand (Botvinick & Cohen, 1998). When they experience this illusion, subjects feel touch on the rubber hand, report that the rubber hand is their hand, and they have a physiological response to threats against the rubber hand. It is not known if proprioceptive signals from muscle receptors can manipulate the sense of body ownership in a similar way. We developed a novel illusion of ownership over a plastic finger, using movement of the index finger as the stimulus. The subject’s finger, which was hidden from the subject, was moved about the proximal interphalangeal (PIP) joint while the subject observed a plastic finger making movements identical to those of their finger. When the illusion was established, naïve subjects (n=30) reported that they felt the movement at the location where they saw the plastic finger and that the plastic finger was their finger. This illusion was induced after a digital nerve block (lignocaine 1%, 3-6 ml), which removes input from skin and joint receptors but leaves intact the muscle receptors in the long flexor and extensor muscles of the fingers. We also measured the impact of the illusion on the perceived position of the finger. Subjects (n=10) were shown a ruler with numbered graduations and asked to identify the number to which their finger was pointing. The plastic finger was 12 cm above the subject’s finger. In a control condition, subjects were accurate with this judgement and reported that their finger was 11.5 [10, 13] cm (median [IQR]) above the table, but after the illusion of ownership over the plastic finger was established, they reported that their finger was 19 [18, 21] cm above the table. This difference was significant (p < 0.005). These results show that proprioceptive signals from muscle receptors can contribute to the sense of body ownership. Furthermore, this illusion of ownership biases the perception of the position of the finger in space.
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