Fig 1.
A forelimb embodiment test in the mouse model.
(A) The two main phases of the embodiment test. Left: Pairing step. During 120 seconds, brush stimulations were applied with brush 1 to the artificial limb (visual input) and with brush 2 to the corresponding forelimb (tactile input), which was hidden from the mouse sight. Right: Testing step. Embodiment of the artificial limb was tested by measuring the intensity of the response of the mouse to a rapidly incoming, sharp object (labeled Threat) that targeted the artificial limb. (B) Time sequence of the experiment. Top: timeline of the pairing and test sections of an individual trial, starting with a 120 s baseline idle time. 120 s of brush paring, followed by the rapid incoming of the threat, which stayed fixed during 10 s. Bottom: example brush stroke times for a synchronous (green) and an asynchronous (red) trial. Line thickness scales are at scale with the 300 ms duration of the brush strokes. (C) Views from the right and left sides of the mouse acquired by high-speed cameras during the pairing stage. Cyan dots: points of interest that are tracked, including the pupil center position and diameter (measured via 2 points in the vertical axis, see close-up) for both eyes, as well as points on the left whisker pad and the left ear.
Fig 2.
Pupil shifts in the direction of the threatened artificial limb are longer after synchronous stimulation.
(A) Example of vertical (top) and horizontal (bottom) movements of the right pupil during a synchronous (green) and an asynchronous (red) trial for one session. The sequence includes a Baseline, Brush strokes pairing, and a threat to the artificial forelimb. (B) Average vertical (top) and horizontal (bottom) movements of the right pupil during synchronous and asynchronous condition trials, normalized to the average position during the 120 s baseline (n = 10 mice). (C) Schematic of the right side of the mouse face during the experiment. Blue arrow: general direction of the pupillary movement following the threat. (D) Spatial trajectory of the right pupil position from 1 s before to 7 s after the threat starts to be displayed. Top: synchronous pairing. Bottom: asynchronous pairing. (E) Top: Average horizontal movements of the right pupil following the threat onset, normalized relative to the average position 1 s before the threat (n = 10). Light background: SEM. Blue arrow: direction of pupil movement as in C. (F) Average difference between the right pupil movements in the two conditions in E. Blue sections: significant differences (Bootstrap based test p < 0.05). Black dashed line: significance threshold. Gray background: W1 and W2 time windows selected for further quantification. (G) Average values of the profiles displayed in E in the time windows identified in F, for all mice. (H) Same as C–G for the left pupil. The data and code underlying this figure is available in the following repository: https://doi.org/10.5281/zenodo.14635566.
Fig 3.
Pupil shifts are shorter when the artificial limb is replaced by a white block.
(A) Schematic of the right side of the mouse during the white block experiment (depicted here in yellow for contrast enhancement of the figure). Blue arrow: general direction of the pupillary movement following the threat. (B) Average horizontal movements of the right pupil after the threat, normalized relative to the average position 1 s before the threat (n = 9 mice). Green line: synchronous pairing. Red line: asynchronous pairing. Light background: SEM. Blue arrow: direction of pupil movement as indicated in A. (C) Average difference between the right pupil movements in the two conditions in B. Blue sections: significant differences (Bootstrap-based test p < 0.05). Black dashed line: significance threshold. Gray background: W1 and W2 time windows selected for further quantification. (D) Average values of the profiles displayed in B in the time windows W1 and W2 for all mice. (E) Average time course of the difference in the right pupil response to the threat between synchronous and asynchronous pairings with the artificial limb (magenta line), and with the white block (yellow line). Light background: SEM. (F) Difference in sync/async contrast in threat response, as computed in E, between the artificial limb and the white block conditions. Blue sections: significant differences (Bootstrap-based test p < 0.05). Black dashed line: significance threshold. Gray background: time windows selected for further quantification. (G) Average values of the profiles displayed in E in the time window identified in F, for all mice. (H) Same as A–G for the left pupil. The data and code underlying this figure is available in the following repository: https://doi.org/10.5281/zenodo.14635566.
Fig 4.
Comparison of the threat reaction with vs. without pairing.
(A) Comparison of the eye movements in the No pairing vs. the Artificial limb conditions, with both synchronous and asynchronous pairing. In the No pairing condition, during 240 s, the mice were idle, and no artifact was presented to the mouse. After this waiting period, the threat was presented. (B) Average horizontal movements of the right pupil following the threat onset, normalized relative to the average position 1 s before the threat (n = 10). Light background: SEM. Black: pupil movements in the threat-only condition without pairing. Green and Red lines: Response to synchronous/asynchronous stimulations of the artificial limb, reproduced from Fig 2E. (C) Top: difference between the horizontal eye movements in response to synchronous pairing of the artificial limb, versus no-pairing. Blue sections: significant differences (Bootstrap-based test p < 0.05). Black dashed line: significance threshold. Bottom: asynchronous pairing versus no-pairing conditions. (D) Same as B for the left pupil horizontal movements. (E) Same as C for the left pupil horizontal movements. (F) Same as A to E for the No pairing versus the Block condition.