Bimanual coupling in amputees with phantom limbs

Abstract

People who experience phantom limbs following amputation sometimes report vivid movements in the phantom, both spontaneous and voluntary^1,2,3. Do these illusory movements reflect the operation of neural mechanisms that govern normal motor performance? By studying interference and coupling effects of the kind that arise during bimanual movements in normal subjects, we show that volitional movements of a phantom arm impose behavioral constraints comparable to those evident in real movement, even when the arm has been missing for over ten years. Thus, the neural mechanisms that generate this coupling continue to operate despite the prolonged absence of any proprioceptive or visual reinforcement. If the amputation was preceded by a peripheral nerve palsy, however, the phantom arm is reported as immobile ('learned paralysis'⁴). We did not observe coupling effects in patients with immobile phantoms.