A team of researchers translated the rubber hand illusion to a mouse model to study the sense of embodiment and found responses similar to human trials. The researchers believe their findings could advance embodiment of prosthetics limbs in humans. A lack of embodiment has been shown to affect use and abandonment of prosthetic devices.
For the study, mice saw an artificial, 3D-printed static replica of their right forelimb at a plausible physiological location while their real limb was hidden from sight. The researchers also conducted the test with a white cube rather than a realistic-looking limb. During a two-minute sequence, the researchers applied mechanically controlled synchronous or asynchronous brush strokes to the real and artificial limbs, then dropped a sharp object toward the artificial limb that was within view of the animal. The mouse’s gaze was tracked with high-speed videography.
Consistent with the literature on the test in humans, the mice focused their gaze on the threat for several seconds when brush strokes were synchronous, but not when they were asynchronous. The behavioral response was also stronger when the artificial forelimb looked similar to a limb versus the cube-shaped object.
According to the authors, this work has practical implications for the study of forelimb embodiment, including mapping the brain circuits of embodiment using genetic and optogenetic research tools that could lead to novel embodiment restoration strategies. The research also supports the idea that rodents can display behavioral correlates of embodiment in settings that are known to trigger embodiment in humans.
“The rubber hand illusion is a staple of the study of body representation in humans, but so far there was no equivalent of this test in the most actionable model: mice. Here we have shown that limb embodiment can be triggered and measured efficiently in mice. This opens up many opportunities to better understand the basic mechanisms of body ownership and apply it for instance, to improve prosthetics.”
The open-access study, “Embodiment of an artificial limb in mice,” was published in PLOS Biology.
