Spinal cord lesions shrink peripersonal space around the feet, passive mobilization of paraplegic limbs restores it

Abstract

Peripersonal space (PPS) is the space surrounding us within which we interact with objects. PPS may be modulated by actions (e.g. when using tools) or sense of ownership (e.g. over a rubber hand). Indeed, intense and/or prolonged use of a tool may induce a sense of ownership over it. Conversely, inducing ownership over a rubber hand may activate brain regions involved in motor control. However, the extent to which PPS is modulated by action-dependent or ownership-dependent mechanisms remains unclear. Here, we explored the PPS around the feet and the sense of ownership over lower limbs in people with Paraplegia following Complete spinal cord Lesions (PCL) and in healthy subjects. PCL people can move their upper body but have lost all sensory-motor functions in their lower body (e.g. lower limbs). We tested whether PPS alterations reflect the topographical representations of various body parts. We found that the PPS around the feet was impaired in PCL who however had a normal representation of the PPS around the hands. Significantly, passive mobilization of paraplegic limbs restored the PPS around the feet suggesting that activating action representations in PCL brings about short-term changes of PPS that may thus be more plastic than previously believed.

Peripersonal space boundaries around the lower limbs

“…Further, some neurophysiological evidence in monkeys suggests that the dorsal areas of the ventral premotor cortex (Muakkassa and Strick 1979;Kurata et al 1985;Kurata 1989) and medial regions of area 7 (Hyvärinen 1981) might be responsible for a 'foot-centered' PPS network, though an investigation using dynamic sensory stimuli was never formally reported. Thus, behavioural studies have uncovered the presence of PPS around the legs and feet (Schicke and Röder 2006;Schicke et al 2009;Van Elk et al 2013;Pozeg et al 2015;Scandola et al 2016;Stettler and Thomas 2016), but no study, to the best of our knowledge, has specifically examined how far PPS extends for the lower body.…”

“…There is at least one investigation that has focused on how the legs' 'potential for action' modulates their PPS representation. In this study, participants with spinal cord injury (SCI), who could not feel or move their legs, completed a crossmodal congruency task wherein vibrations were administered to the hands, and light flashes appeared near the feet (Scandola et al 2016). To obtain a crossmodal congruency effect (CCE) in this case, the expectation is that tactile reaction times are facilitated when the visual stimulus is ipsilateral (congruent) to the tactile location, and conversely, hindered when the visual stimulus occurs contralateral (incongruent) to the tactile stimulus.…”

“…Yet, as only static visual stimuli were used, and tactile detection was not assessed, it was not specified at what point in space multisensory integration (i.e., the boundaries of PPS) might occur around the feet. Certainly, some investigations have focused on the integration of visual and tactile information within PPS around the feet (Schicke and Röder 2006;Schicke et al 2009;Van Elk et al 2013;Scandola et al 2016). For example, Schicke et al (2009) were one of the first groups to show (behaviourally) that a PPS representation around the feet exists using a crossmodal congruency task.…”

Audio Spatial Representation Around the Body

“…All these findings together suggest that different parts of the space around us may be differently organized, based on the dominant perceptual system for that portion of space and they could be differently shaped by motor activity. To date, most studies have focused on studying audio perception in the front and back space ( Farnè and Làdavas, 2002 ; Zampini et al, 2007 ) or in high and low space ( Heed and Röder, 2010 ; Scandola et al, 2016 ) separately, or they have studied the effect of actions on audio perception ( Weiss et al, 2011 ; Timm et al, 2014 ; Viaud-Delmon and Warusfel, 2014 ). Here we study all these aspects in a unique framework by using unitary approach.…”

Lower limb peripersonal space and the desire to amputate a leg

“…For example, passively moving the legs of paralyzed individuals restores PPS around the legs (Scandola et al, 2016), emphasizing the tight link between PPS and action. A second explanation as to why a PPS might be maintained in the absence of ownership is the physical and sensory congruence of the leg with the body.…”