Abstract
Unilateral major limb amputation causes changes in sensory perception. Changes may occur within not only the residual limb but also the intact limb as well as the brain. We tested the hypothesis that limb amputation may result in the detection of hand sensation during stimulation of a non-limb-related body region. We further investigated the responses of unilateral upper limb amputees and individuals with all limbs intact to temporally based sensory tactile testing of the fingertips to test the hypothesis that changes in sensory perception also have an effect on the intact limb. Upper extremity amputees were assessed for the presence of referred sensations (RSs)—experiencing feelings in the missing limb when a different body region is stimulated, to determine changes within the brain that occur due to an amputation. Eight of 19 amputees (42.1%) experienced RS in the phantom limb with manual tactile mapping on various regions of the face. There was no correlation between whether someone had phantom sensations or phantom limb pain and where RS was found. Six of the amputees had either phantom sensation or pain in addition to RS induced by facial stimulation. Results from the tactile testing showed that there were no significant differences in the accuracy of participants in the temporal order judgment tasks (p = 0.702), whereby participants selected the digit that was tapped first by a tracking paradigm that resulted in correct answers leading to shorter interstimulus intervals (ISIs) and incorrect answers increasing the ISI. There were also no significant differences in timing perception, i.e., the threshold accuracy of the duration discrimination task (p = 0.727), in which participants tracked which of the two digits received a longer stimulus. We conclude that many, but not all, unilateral upper limb amputees experience phantom hand sensation and/or pain with stimulation of the face, suggesting that there could be postamputation changes in neuronal circuitry in somatosensory cortex. However, major unilateral limb amputation does not lead to changes in temporal order judgment or timing perception tasks administered via the tactile modality of the intact hand in upper limb amputees.
Highlights
Great debate ensues regarding the etiology of phantom limb sensations (PLSs) and associated pain
Results from this study indicate that cortical reorganization may be confined to the contralateral somatosensory cortex and does not significantly affect other cortical areas or spread transcallosally to the somatosensory cortex in the opposite hemisphere
This study showed that cortical reorganization is not always directly linked to the experience of phantom limb pain (PLP), since half of those experiencing mislocalization of touch failed to report any PLP
Summary
Great debate ensues regarding the etiology of phantom limb sensations (PLSs) and associated pain. The minority that tends not to experience any phantom sensations typically includes congenital amputees [3, 4], one study has identified such experiences in this population [5]. More than 80% of all amputees will experience phantom limb pain (PLP), characterized by electric shock, stabbing, and cramping sensations [6]. The mechanisms that create phantom experiences, including sensation and pain, are not understood. The peripheral limb is removed from the body causing drastic changes in the peripheral and in the central nervous systems. Several imaging studies have shown that, after an amputation, cortical representations of adjacent remaining body parts take over the cortical area that once responded to the amputated region. The face-representing somatosensory cortical region expands and takes over the arm area in upper extremity amputees [3, 8,9,10,11]
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