Abstract
Background: Studies in animals and humans indicate that the interruption of body-brain connections following spinal cord injury (SCI) leads to plastic cerebral reorganization.Objective: To explore whether inducing the Rubber Hand Illusion (RHI) via synchronous multisensory visuo-tactile bodily stimulation may reveal any perceptual correlates of plastic remapping in SCI.Methods: In 16 paraplegic, 16 tetraplegic and 16 healthy participants we explored whether RHI may be induced by tactile stimuli involving not only the left hand but also the left hemi-face. Touching the participants actual hand or face was either synchronous or asynchronous with tactile stimuli seen on a rubber hand. We assessed two components of the illusion, namely perceived changes in the real hand in space (indexed by proprioceptive drift) and ownership of the rubber hand (indexed by subjective responses to an ad-hoc questionnaire).Results: Proprioceptive drift and ownership were found in the healthy group only in the condition where the left real and fake hand were touched simultaneously. In contrast, no drift was found in the SCI patients who, however, showed ownership after both synchronous and asynchronous hand stroking. Importantly, only tetraplegics showed the effect also after synchronous face stroking.Conclusions: RHI may reveal plastic phenomena in SCI. In hand representation-deprived tetraplegics, stimuli on the face (represented contiguously in the somatic and motor systems), drive the sense of hand ownership. This hand-face remapping phenomenon may be useful for restoring a sense of self in massively deprived individuals.
Highlights
Spinal cord injuries (SCI) cause an irreversible disconnection between the body and the brain
In 16 paraplegic, 16 tetraplegic and 16 healthy participants we explored whether Rubber Hand Illusion (RHI) may be induced by tactile stimuli involving the left hand and the left hemi-face
While cervical SCI leads to tetraplegia, a clinical condition with impaired sensory-motor functions in both upper and lower limbs, SCI below the seventh cervical spinal cord segment leads to paraplegia, where deficits affect lower but not upper limbs
Summary
Spinal cord injuries (SCI) cause an irreversible disconnection between the body and the brain This disconnection implies a deprivation of somatosensory input to and motor output from the brain. In initial studies of the RHI healthy individuals were asked to look at a rubber hand that was stroked by the examiner, synchronously or asynchronously with their hidden from view real hand It appeared that only during synchronous stimulation was the rubber hand perceived as part of the participants’ own body (index of ownership of an artificial hand) and the position of the real hand was perceived as having shifted toward the rubber hand (“proprioceptive drift,” index of illusory perception of body in space) (Botvinick and Cohen, 1998; Ehrsson et al, 2005; Tsakiris and Haggard, 2005; Longo et al, 2008; Mohan et al, 2012; Schaefer et al, 2013). Studies in animals and humans indicate that the interruption of body-brain connections following spinal cord injury (SCI) leads to plastic cerebral reorganization
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