Mental rotation of body parts and embodied assistive tool in patients with spinal cord injury

The adoption of innovative assistive werable robotics (WR), including exoskeletons (EXO) as gait rehabilitation and assistance after SCI has an impact on brain reorgnization influencing body representation, body ownership and sense of agency. Traditionally, researchers have studies embodiment of assistive tool by quantifying how users interact with the environment with a focus on wheelchair and the improvement on motor imagery after training. We investigated individuals with spinal cord injuries (SCI) included that participated to an EXO training to find out: 1. how the loss of sensory sensitivity and motor function in the body part below the level of injury influences body imagery; 2. if a users reacts to rotation of an assistive tool in a similar way they might react to rotation of their own body. To this aim a group of 20 male patients with SCI (lesion from T4 to L2, time since lesion: 11(SD: 6.34 years) as compared to 20 age matched healthy control considering differences and impact of training in body representation and embodiment of biological (i.e., lower and upper limbs) and non-biological (i.e., assistive tools; wheelchair; EXO) objects. A mental rotation task adopting the two categories of objects (biological; non biological) were administered (16 practice trials; 48 experimental trials). Participants verbally indicated whether the stimulus, with four different orientation (0°, 90°, 180°, 270° ) was presented in left or right side despite spatial orientation. Reaction times (RTs) were collected. Two measurements were collected for both the groups (T0, T1). For SCI patients T1 took place after assisted EXO training program (8 sessions in 4 weeks). Mixed ANOVAs on RTs emerged, but faster RTs in biological limb rotation in both the groups were highlighted. Interestingly, healthy participants performed slower RTs than SCI in wheelchair and lower limbs rotation. Moreover, within-group differences in SCI highlighted a significant effect of training in RTs of EXO rotation (RTs of T0 higher than T1). The study highlighted two main results. Firstly, the pattern of response times to stimuli at various orientation suggests that SCI patients did not show a linear increase in RTs as a function of rotation angle of the foot pictures; and secondly, the improvement of EXO rotation indicated a positive effect of training in WR embodiment, which can promote a positive effect of both motor and sensory rehabilitation.