Functional reorganization of the primary somatosensory cortex of a phantom limb pain patient

Abstract

Functional reorganization of the somatosensory system was widely observed in phantom limb pain patients. Whereas some studies demonstrated that the primary somatosensory cortex (S1) of the amputated limb was engaged with the regions around it, others showed that phantom limb pain was associated with preserved structure and functional organization in the former brain region. However, according to the law of use and disuse, the sensitivity of S1 of the amputated limb to pain-related context should be enhanced due to the adaptation to the long-lasting phantom limb pain experience. Here, we collected neurophysiological data from a patient with 21-year phantom limb pain using electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) techniques. EEG data showed that both laser-evoked potentials (LEPs) and tactileevoked potentials (TEPs) were clearly presented only when radiant-heat laser pulses and electrical pulses were delivered to the shoulder of the healthy limb, but not of the amputated limb. This observation suggested the functional deficit of somatosensory pathways at the amputated side. FMRI data showed that significant larger brain activations by painful rather than non-painful stimuli in video clips were observed not only at visual-related brain areas and anterior/mid-cingulate cortex, but also at S1 contralateral to the amputated limb. This observation suggested the increased sensitivity of S1 of the amputated limb to the pain-related context. In addition, such increase of sensitivity was significantly larger if the context was associated with the amputated limb of the patient. In summary, our findings provided novel evidence for a possible neuroplasticity of S1 of the amputated limb: In an amputee with long-lasting phantom limb pain, the sensitivity of S1 to pain-related and amputated-limb-related context was greatly enhanced.