PLASTICITY OF PLASTICITY - CHANGES IN THE PATTERN OF PERCEPTUAL CORRELATES OF REORGANIZATION AFTER AMPUTATION

We report a follow-up study on seven arm amputees in whom magnetic sou rce imaging had originally revealed a strong correlation between the a mount of cortical invasion of the deafferented cortex and the amount o f pain evoked sensation mislocalized to the phantom limb. This re-exam ination Mins performed in order to corroborate the phenomenon of mislo calization. On follow-up examination for mislocalization 4 weeks later a close correlation had remained between the original amount of corti cal representational reorganization of the amputation zone (at the fir st examination) and the number of sites from where painful stimuli evo ked sensations referred to the phantom limb, i.e. the amount of percep tual mislocalization, at the second examination. However contrary to o ur expectation, the topography of referred sensation had completely ch anged in every patient. These results suggest that while the overall e xtent of reorganization is a rather stable phenomenon, the concomitant changes in the pattern of sensory processing are not. This may be due to the fact that alterations of sensory processing are not hardwired, but are rather mediated by an extensive and interconnected neural net work with fluctuating synaptic strengths. This mechanism may be of imp ortance for neurological rehabilitation.