Feeling ownership of our limbs represents a fundamental aspect of self-consciousness, and in some circumstances, the feeling is extended out of our own body, as in the rubber hand illusion (RHI, Botvinick and Cohen, 1998). In the RHI, when a rubber hand and a participant's own hand are synchronously stroked, the participant feels that the rubber hand is his/her own hand. We have developed a rubber tail task in mice, aiming to evaluate their body ownership (Wada et al., 2014).
Mice were trained to remain in a small tube with their heads stationary (n = 5). The mice underwent daily tests comprising two conditions: 1) real tails and rubber tails were synchronously stroked using a brush; 2) the stimuli were always administered synchronously; however, in this study, the rubber tail was occluded by an opaque plastic plate to evaluate the importance of visual stimuli. After the tails were stroked for more than 1 min, an experimenter firmly grasped the rubber tail, and the responses of the mice were evaluated.
After synchronous stroking (condition 1), the mice responded as if their own tails were being touched when the rubber tails were grasped (0.44 ± 0.048). When the rubber tail was occluded by an opaque plastic plate (condition 2), the responses were significantly decreased (0.17 ± 0.048, P < 0.05, paired t-test).
This finding suggests that visuotactile integration is important for the RHI-like phenomenon in mice, and these observations are consistent with the RHI in humans. We infer that mice may experience body ownership of their tail. This phenomenon may be applicable for evaluation of body image in animals, and future research using this animal model may provide novel insights into developmental disabilities or psychiatric disorders.