“Anomalous” Representations and Perceptions: Implications for Human Neuroplasticity

Abstract

Changes in the perception and representation of the body observed inbrain damaged and amputee patients hint at the plastic nature of thebody schema. Evidence for integration of external objects into the bodyschema comes from a woman with a large right-hemisphere stroke whoaffirmed that the paralysed left hand was not her own but belonged tosomeone else. Although able to see and describe the rings she had wornfor years and was currently wearing on her left, now disowned hand, thispatient resolutely denied their ownership. By contrast, she had nodifficulties in recognising these rings as her own when they wereshifted to her right hand, or displayed by the examiner in front of her.Similarly, she promptly acknowledged ownership of other personalbelongings that in her previous experience had not been ordinarilyassociated with the left hand (e.g., a comb). Complex dynamic aspects ofthe body schema are also revealed by the recent evidence in limb orbreast amputees that vivid phantom sensations can arise as a result oftactile stimulations applied to body regions distant from the amputationline. Sensations in the phantom hand, for example, can be elicited bytactile stimuli delivered to the lower face on the side of theamputation. Like the concurrent veridical facial sensations, the evokedphantom sensations may convey precise information about differentfeatures of the facial stimuli. Given the representional contiguity offace and hand, phantom hand sensations from facial stimulation areprobably caused by an appropriation of the original somatosensoryrepresentation of the lost hand by sensory inputs inherent to theadjacent face representation.The representation of the body however, has some aspects of stability.Observations in amputees indicate, for example, that phantom perceptionsmay persist over decades, thus suggesting that parts of the brain may bequasi-permanently committed to the representation of a given body part.In the same vein, stimulation of the somatosensory cortex in amputeeswho do not feel any phantom perceptions may resurrect the phantom limbeven 25 years after the amputation.