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

Acoustic stimuli are processed throughout the auditory projection pathway, including the neocortex, by neurons that are aggregated into 'tonotopic' maps according to their specific frequency tunings. Research on animals has shown that tonotopic representations are not statically fixed in the adult organism but can reorganize after damage to the cochlea or after training the intact subject to discriminate between auditory stimuli. Here we used functional magnetic source imaging (single dipole model) to measure cortical representations in highly skilled musicians. Dipole moments for piano tones, but not for pure tones of similar fundamental frequency (matched in loudness), were found to be enlarged by about 25% in musicians compared with control subjects who had never played an instrument. Enlargement was correlated with the age at which musicians began to practise and did not differ between musicians with absolute or relative pitch. These results, when interpreted with evidence for modified somatosensory representations of the fingering digits in skilled violinists, suggest that use-dependent functional reorganization extends across the sensory cortices to reflect the pattern of sensory input processed by the subject during development of musical skill.

Neuromagnetic fields were recorded from human subject as they listened selectively to sequences of rapidly presented tones in one ear while ignoring tones of a diferent pitch In the oppoite ear. in the interval 20-50 msec (the P20-50) was also found to be enlarged with attention (6, 7).These ERP results support the view that the flow of auditory sensory information can be altered by attention at a relatively early stage of processing. They do not specify, however, the brain structures in which this stimulus selection takes place. One approach to address this question is to study neuromagnetic recordings (ERFs), which offer an advantage over ERPs for localization of the anatomical sources of evoked brain activity in cortical sulci (e.g., auditory cortex on the supratemporal plane). This advantage is due to ERF recordings being selectively sensitive to activity from such sources and due to magnetic fields being less distorted by the skull (8, 9).Several studies have applied source localization techniques to ERF recordings and concluded that at least part of the enhanced activity elicited by attended sounds in the N100 latency range arises from the vicinity of auditory cortex (10, 11). However, the precise anatomical source(s) of this attention effect have yet to be verified by superposition of calculated source coordinates onto magnetic resonance (MR) images of the subjects' brains.11 Even less information is available regarding the neural generator(s) ofthe P20-50 ERP attention effect, as no magnetic counterpart ofthis very early ERP modulation has yet been reported.In the current study, neuromagnetic and MR imaging techniques were combined to localize the neuroanatomical origins of the early effects of attention on tone-evoked brain activity. The results provide evidence that focused auditory attention exerts selective control over early sensory processing in the auditory cortical areas on the supratemporal plane beginning at 20 msec poststimulus. METHODSSelective auditory attention was studied using the same fast-rate dichotic listening paradigm that we have used previously in ERP studies (6, IThere is considerable evidence that at least some of the "exogenous" tone-evoked activity (i.e., non-attention-related) in the 30-to 150-msec latency range arises from neural generators in the vicinity of the auditory cortex on the supratemporal plane (12)(13)(14)(15). Recent neuromagnetic studies have localized portions ofthis early sensoryevoked activity to the supratemporal-plane auditory cortex as visualized on subjects' MR scans (16-18). 8722

This paper presents data concerning auditory evoked responses in the middle latency range (wave Pam/ Pa) and slow latency range (wave Nlm/Nl) recorded from 12 subjects. It is the first group study to report multi-channel data of both MEG and EEG recordings from the human auditory cortex. The experimental procedure involved potential and current density topographical brain mapping as well as magnetic and electric source analysis. Responses were compared for the following 3 stimulus frequencies: 500, 1000 and 4000 Hz. It was found that two areas of the auditory cortex showed mirrored tonotopic organization; one area, the source of Nlm/Nl wave, exhibited higher frequencies at progressively deeper locations, while the second area, the source of the Pam/Pa wave, exhibited higher frequencies at progressively more superficial locations. The Pa tonotopic map was located in the primary auditory cortex anterior to the Nlm/Nl mirror map. It is likely that Nlm/Nl results from activation of secondary auditory areas. The location of the Pa map in AI, and its NI mirror image in secondary auditory areas is in agreement with observations from animal studies.