Patients who are paralyzed on one side following a stroke often experience the feeling of having an extra limb, much like phantom limbs described by people who have undergone amputations. For the most part, patients cannot see or intentionally move these supernumerary phantom limbs (SPL). However, in some unusual cases, patients have reported seeing the limb and experiencing feeling objects or body parts with it.
A study, which was recently published in Annals of Neurology, was conducted by researchers from Geneva University Hospitals to investigate brain activity connected to SPLs. The study involved a 64-year-old woman who was paralyzed on her left side, but had reported experiencing an SPL that she said she could feel and intentionally move. According to the study, the woman began experiencing an SPL from the elbow of her paralyzed left arm, which she described as “milk white and transparent” just days after suffering the stroke. She claimed that she could intentionally trigger the SPL to touch her head and shoulder. When she used it to scratch her head, she said she experienced relief.
To determine if there was actual brain activity associated with the SPL, the researchers conducted magnetic resonance imaging scans to analyze her brain activity during the actual and imagined movements of her healthy right hand, as well as the imagined movements of her paralyzed left hand and movements of the SPL. Among their findings, the researchers discovered that when the patient was asked to scratch her cheek with the SPL, areas of the brain associated with movement and vision were activated, confirming her report that she could see and move her phantom limb. Scratching her left cheek with the SPL also triggered a measurable sensory response.
“Existing evidience from stroke-elicited SPLs convincingly implicates the mismatch between the subject’s well-established sensorimotor representations and a suddenly aberrant pattern of communication between the brain and the paralyzed limb,” the authors state, adding that the current case may represent a missing link between classical phantom limbs and autoscopic phenomena such as out-of-body experiences. “Ultimately, however, these conditions might offer a unique way to understand how the brain constructs a normal experience of bodily awareness and the self,” they conclude.
News Release: Study shows brain activity associated with phantom limbs www.jp.blackwellpublishing.com March 25, 2009
