Brain Plasticity After Amputation Using Magnetic Resonance Spectroscopy

Amputation usually leads to permanent disability in amputees accompanied by long-term peripheral discomforts or abnormal sensations,including phantom limb sensation,phantom limb pain,stump sensation and stump pain.Neuroimaging studies have revealed that peripheral deafferentation or denervation may cause abnormal activations or altered functions in specific cortical regions.It was suggested that these brain plasticity changes may be related to the physiological or metabolic abnormalities in the central nervous system.Currently,metabolic changes following amputation in human beings have rarely been reported yet.The physiological and metabolic mechanisms underlying the abnormal sensations and pains after amputation also need to be investigated.In this thesis,therefore,we used magnetic resonance spectroscopy(MRS)to study the metabolic changes of two crucial brain regions along the sensory pathway,i.e.thalamus and secondary somatosensory cortex(SⅡ),after amputation.Moreover,we assessed the levels of pain and abnormal sensation for the amputees,as well as their stump usages in daily life,in order to investigate brain plasticity after amputation from a comprehensive perspective.By comparing neural metabolic changes between amputees and healthy controls,we found declines of the choline-containing compounds(Cho)and N-acetylaspartate(NAA)concentrations in the contralateral thalamus and SⅡ areas in amputees,indicating neuronal loss and dysfunctions in these brain regions after amputation.In the meantime,the metabolic changes in amputees were highly associated with the occurrence or magnitude of the pain or abnormal sensation on the stump or the phantom limb,suggesting that brain plasticity or reorganization may be related to these sensations or pains.Specifically,(1)the amputees with phantom or stump sensations presented higher Cho or NAA levels than those without these sensations,suggesting that these sensations may contribute to less neural damage or degeneration in amputees,and reflect more preserved brain functions after amputation.(2)The amputees with stump pain,however,showed more reduction of Cho and NAA in the SⅡ area,indicating that the cortex damages following amputation may contribute to the pain.(3)In addition,the magnitude of stump pain was highly correlated with multiple factors,including stump length,stump usage and the NAA level in the SⅡ area.Inferred from these results,the pain after amputation may be mediated by different factors or pathways,including but not limited to a metabolic regulation and a mediation from the motor pathway.Finally,we suggested that intensive use and exercise of the stump could effectively relieve amputees from pain,and also promote the recovery and rehabilitation of the nervous system after amputation-caused damages.Combing MRS with the assessment of sensations,pains and stump usages,this study investigated neural metabolic mechanisms underlying brain reorganization and abnormal sensations after amputation,and provided physiologic evidences of the brain plasticity after amputation.