Beyond re-membering: Phantom sensations of congenitally absent limbs

Abstract

Phantom limbs are traditionally conceptualized as the phenomenal persistence of a body part after deafferentation. Previous clinical observations of subjects with phantoms of congenitally absent limbs are not compatible with this view, but, in the absence of experimental work, the neural basis of such ''aplasic phantoms'' has remained enigmatic. In this paper, we report a series of behavioral, imaging, and neurophysiological experiments with a university-educated woman born without forearms and legs, who experiences vivid phantom sensations of all four limbs. Visuokinesthetic integration of tachistoscopically presented drawings of hands and feet indicated an intact somatic representation of these body parts. Functional magnetic resonance imaging of phantom hand movements showed no activation of primary sensorimotor areas, but of premotor and parietal cortex bilaterally. Movements of the existing upper arms produced activation expanding into the hand territories deprived of afferences and efferences. Transcranial magnetic stimulation of the sensorimotor cortex consistently elicited phantom sensations in the contralateral fingers and hand. In addition, premotor and parietal stimulation evoked similar phantom sensations, albeit in the absence of motor evoked potentials in the stump. These data indicate that body parts that have never been physically developed can be represented in sensory and motor cortical areas. Both genetic and epigenetic factors, such as the habitual observation of other people moving their limbs, may contribute to the conscious experience of aplasic phantoms.

Differential influence of hands posture on mental rotation of hands and feet in left and right handers

“…This last point is compatible with less extreme handedness scores in our left-handed participants (if compared to the right-handed participants) and the observation that right handers processed right stimuli (hands and feet) faster than left stimuli. Faster RTs for mental rotation of right body parts with respect to left body parts has been reported by several studies involving right-handed healthy participants (Parsons 1987;Gentilucci et al 1998;Ionta et al 2007;Funk and Brugger 2008), upper limb amputees (Nico et al 2004) and congenital amputees (Brugger et al 2000), suggesting that right handers are generally faster with right body parts. Our data support these previous Wndings and also extend them by showing that left-handed participants did not show either laterality preference and indicating that mental rotation of body parts depends at least on motor (and/or proprioceptive) and visual mechanisms that seem to interact diVerently in right-and left-handed people.…”

Synthetic consciousness: the distributed adaptive control perspective

“…A further variation on the role of embodiment in the nature of consciousness is the passive frame theory of Morsella that ascribes to consciousness the central role of facilitating the control of the skeletal-muscle system [41]. Challenges to this perspective are cases where embodiment is disrupted as in locked-in syndrome, phantom limb pain or for subjects born without limbs who yet experience them [42]. (ii) Conscious experience is defined in the sensorimotor contingencies of the agent environment interaction.…”

Distorted Body Representations in Healthy Cognition

“…Phantoms occur in a substantial majority of cases of amputation (Melzack, 1992), and less frequently following congenital limb absence (Brugger et al, 2000). The subjectively felt presence of the missing limb can be so strong that the patient may even try to walk with a phantom leg (Melzack, 1990).…”