ALTHOUGH phantom-limb pain is a frequent consequence of the amputation of an extremity, little is known about its origin l -4.On the basis of the demonstration of substantial plasticity of the somatosensory cortex after amputationS or somatosensory deafferentation in adult monkeys6, it has been suggested that cortical reorganization could account for some non-painful phantom-limb phenomena in amputees and that cortical reorganization has an adaptive (that is, pain-preventing) function 2 ,s,7,8. Theoretical and empirical work on chronic back pain 9 ,lo has revealed a positive relationship between the amount of cortical alteration and the magnitude of pain, so we predicted that cortical reorganization and phantom-limb pain should be positively related. Using non-invasive neuromagnetic imaging techniques to determine cortical reorganization in humans ll -13, we report a very strong direct relationship (r = 0.93) between the amount of cortical reorganization and the magnitude of phantom limb pain (but not non-painful phantom phenomena) experienced after arm amputation. These data indicate that phantom-limb pain is related to, and may be a consequence of, plastic changes in primary somatosensory cortex.A brief telephone interview was used to obtain information about the amount of phantom-limb pain in 65 upper-limb ampu-482 tees. This information served as the sole basis for the selection of a representative sample of 13 subjects with widely varying degrees of phantom-limb pain. The mean age of the 13 subjects was 50.1 years (s.d. = 17,2, range 27-73 yr), mean post-amputation time was 24.3 years (s.d. = 19.8, range I to 51 yr). Twelve men and one woman participated in the study, Traumatic injury in ten cases and osteosarcoma in three cases had made the amputation necessary. Cortical reorganization was determined by magnetic source imaging' , using the method illustrated in Fig. 1. The subjects underwent a comprehensive neurological and psychological investigation which included detailed assessments of phantom pain and phantom sensations, stump pain and stump sensations, pre-amputation pain, telescoping (the subjective experience of the phantom limb retracting towards and often disappearing in the stump), and facial remapping (the appearance of phantom sensations upon non-painful stimulation of the face with isomorphism between facial stimulation sites and the location of phantom sensations) (Fig. 2 legend).A large significant positive linear relationship was found between the amount of phantom-limb pain, as measured on the standardized pain-intensity scale, and the amount of cortical reorganization (r=0.93, P

Magnetic source imaging revealed that the cortical representation of the digits of the left hand of string players was larger than that in controls. The effect was smallest for the left thumb, and no such differences were observed for the representations of the right hand digits. The amount of cortical reorganization in the representation of the fingering digits was correlated with the age at which the person had begun to play. These results suggest that the representation of different parts of the body in the primary somatosensory cortex of humans depends on use and changes to conform to the current needs and experiences of the individual.Evidence has accumulated over the past rwo decades that indicares that alterations in afferent input can induce plastic reorganizational ch

Late gamma activity may represent a correlate of widespread cortical networks processing different aspects of emotionally arousing visual objects. In contrast, differences between affective categories in early gamma activity might reflect fast detection of aversive stimulus features.

Steady-state responses (SSRs) or steady-state fields (SSFs) show maximum amplitude when tone pulses are presented at repetition rates near 40 Hz. This result has led to the hypothesis that the SSR/SSF consists of superimposed transient 'middle latency' responses which display wave periods near 40 Hz and summate with one another when phase locked by 40 Hz steady-state stimulation. We evaluated this hypothesis by comparing the cortical sources of the 40 Hz auditory SSF with sources of the middle latency Pa wave which is prominent in electrical and magnetic recordings, and with the cortical sources of the familiar N1 wave, at different carrier frequencies between 250 and 4000 Hz. SSF sources determined for the different carrier frequencies were found to display a 'medial' tendency tonotopy resembling that of the N1m (sources for the higher frequencies represented more deeply within the supratemporal sulcus), opposite the 'lateral' tendency tonotopy of the middle latency Pam (sources for the higher frequencies situated more laterally). A medial SSF tonotopy was observed in each of the subjects investigated, including three subjects for whom Pam and N1m maps were also available. These findings suggest that the 40 Hz SSF may not consist of summated or entrained middle latency responses, as has previously been proposed. Alternative mechanisms for the SSR are discussed.

The relationship between phantom limb phenomena and cortical reorganization was examined in five subjects with congenital absence of an upper limb and nine traumatic amputees. Neuromagnetic source imaging revealed minimal reorganization of primary somatosensory cortex in the congenital amputees (M=0.69 cm, SD 0.24) and the traumatic amputees without phantom limb pain (M=0.27 cm, SD 0.25); the amputees with phantom limb pain showed massive cortical reorganization (M=2.22 cm, SD 0.78). Phantom limb pain and nonpainful phantom limb phenomena were absent in the congenital amputees. Whereas phantom limb pain was positively related to cortical reorganization (r=0.87), nonpainful phantom phenomena were not significantly correlated with cortical reorganization (r=0.34). Sensory discrimination was normal and mislocalization (referral of stimulation-induced sensation to a phantom limb) was absent in the congenital amputees. The role of peripheral and central factors in the understanding of phantom limb pain and phantom limb phenomena is discussed in view of these findings.