Tuesday, 12 March 2013

The 'extended body': SCI patients feel that their wheelchair is integrated with their body!

Research published on March 6th in the open access journal PLOS ONE (Public Library Of Science), carried out by Mariella Pazzaglia and colleagues from Sapienza University in Italy, found that a significant number of the participants in their study experienced their wheelchair as being 'internal to the corporeal boundary, suggesting a revision in their body image". The researchers explain that a prosthetic device that extends or restores movement may become part of the identity of the person to whom it belongs. Pazzaglia and colleagues state that "some individuals with spinal cord injury (SCI) adapt their body and action representation to incorporate their wheelchairs". 

To explore whether the bodily assimilation of a relevant external tool develops as a consequence of altered sensory and motor inputs from the body or of prolonged confinement sitting or lying in the wheelchair, the authors used principal component analysis (PCA) on the reports they collected from 55 consenting wheelchair-bound individuals with SCI. These reports contained detailed introspective experiences of wheelchair use. It was reported in this study that all of the participants used their wheelchair for approx 13 hours a day and none had experienced head or brain lesions associated with their SCI, as documented by MRI. 

Using a rating scale ranging from 0 (“completely disagree”) to 7 (“completely agree”), participants evaluated questions that were designed to capture the implicit and explicit tool and body experiences. Wheelchair embodiment among SCI patients was determined based on 11 different questionnaire statements. It was found that regular use of a wheelchair induced the perception that the body’s edges are not fixed, but are instead plastic and flexible to include the wheelchair. Principle component analysis revealed  three major components, (1) the functional aspect of the sense of embodiment concerning the wheelchair appeared to be modulated by disconnected body segments, (2) no effect of time since injury nor an effect of exposure to/experience of was detected and (3) patients with lower spinal cord injuries who retained upper body movement showed a stronger association of the wheelchair with their body (functional embodiment) than those who had spinal cord impairments in the entire body.

"These findings suggest that the brain can incorporate relevant artificial tools into the body schema via the natural process of continuously updating bodily signals. Rather than being thought of only as an extension of the immobile limbs, the wheelchairs had become tangible, functional substitutes for the affected body part. Pazzaglia claims that the corporeal awareness of the tool emerges not merely as an extension of the body but as a substitute for, and part of, the functional self. "This ability to embody new essential objects extends the potentiality of physically impaired persons and can be used for their rehabilitation". 

According to Pazzaglia, the participants' brains go into an automatic mode when it comes to using the wheelchairs. This leads to "more efficient and safer use, with lower costs, risks and dangers to the body,". To elude dangerous objects in the environment and the collisions that may occur during wheelchair use, the brain needs to encode an internal representation of the body that includes the wheelchair. "Moreover, the simple action of picking objects up from the floor without tipping out of the wheelchair implies a change in the representation of the body to enable this to happen successfully and without the risk of possible damage to the individual due to a fall. All daily activities become an automatic way of thinking, not merely a mechanical or practical process."

Previous studies (1 & 2) have indicated that individuals with prosthetic devices that extend or restore movement may make such tools part of their physical identity, but whether this integration was due to prolonged use or a result of altered sensory input was unclear. Based on the results of this study, Pazzaglia and colleagues suggest that it may be the latter, as the brain appears to continuously update bodily signals to incorporate these tools into a sense of the body. 

Although the authors recognize that 'the phenomenal reports from SCI individuals cannot be generalized to all occurrences of corporeal awareness of a tool, they do offer an initial step towards the determination of clearly dissociable sub-components of prosthetic device embodiment'. Pazzaglia states that in the future, this kind of research could lead to ways to enhance the body in people who are physically impaired - "Bodily representations can be extended to include exoskeletons, prostheses, robots and virtual avatars". Aside from the fact that the results from this study may aid and have applications in the rehabilitation of physically impaired people, it only reaffirms the advantages and ever expanding picture we are getting from areas of research that adopt and recognize the benefits of an embodied approach. For an interesting and somewhat heartfelt first person perspective of how one in a wheelchair sees it as being part of themselves, their body, click here.


  1. Small point: The journal is not "Plus one", but PLoS one, where PLoS stands for Public Library of Science.

  2. This reminded me of post-amputation pain, and phantom sensation where patients experience pain in their absent limb. I guess this is just another example of mind over matter. You can read more about it here: http://www.amputee-coalition.org/inmotion/mar_apr_98/pain_mgt/page1.html
    Thank you for the reading.