Cortical reorganization and phantom phenomena in congenital and traumatic upper-extremity amputees

Congenital foot deformation alters the topographic organization in the primate somatosensory system

Limbs may fail to grow properly during fetal development, but the extent to which such growth alters the nervous system has not been extensively explored. Here we describe the organization of the somatosensory system in a 6-year-old monkey (Macaca radiata) born with a deformed left foot in comparison to the results from a normal monkey (Macaca fascicularis). Toes 1, 3, and 5 were missing, but the proximal parts of toes 2 and 4 were present. We used anatomical tracers to characterize the patterns of peripheral input to the spinal cord and brainstem, as well as between thalamus and cortex. We also determined the somatotopic organization of primary somatosensory area 3b of both hemispheres using multiunit electrophysiological recording. Tracers were subcutaneously injected into matching locations of each foot to reveal their representations within the lumbar spinal cord, and the gracile nucleus (GrN) of the brainstem. Tracers injected into the representations of the toes and plantar pads of cortical area 3b labeled neurons in the ventroposterior lateral nucleus (VPL) of the thalamus. Contrary to the orderly arrangement of the foot representation throughout the lemniscal pathway in the normal monkey, the plantar representation of the deformed foot was significantly expanded and intruded into the expected representations of toes in the spinal cord, GrN, VPL, and area 3b. We also observed abnormal representation of the intact foot in the ipsilateral spinal cord and contralateral area 3b. Thus, congenital malformation influences the somatotopic representation of the deformed as well as the intact foot.

Modulation of non-painful phantom sensation in subjects with spinal cord injury by means of rTMS

We aimed in this study to investigate whether repetitive transcranial magnetic stimulation (rTMS), given as theta burst stimulation (TBS), can interfere with non-painful phantom sensations in subjects with spinal cord injury (SCI). In double-blind, sham-controlled experiments in five subjects with cervical or thoracic traumatic SCI, we evaluated the effects of a single session of inhibitory (continuous) TBS, excitatory (intermittent) TBS, or placebo TBS, on simplex and complex non-painful phantom sensations. The interventions targeted the contralateral primary motor cortex (M1), the primary sensory cortex (S1) and the posterior parietal cortex (PPC). Measurements were carried out at baseline (T0), 5 min (T1) and 30 min later (T2) after the intervention. Descriptive evaluation of results shows that non-painful phantom sensations were not affected by rTMS applied over M1. Continuous (inhibitory) TBS over S1 induced a short-lasting decrease of simple non-painful phantom sensations, while continuous TBS over PPC induced a short-lasting decrease of both simple and complex phantom sensations. Intermittent (excitatory) TBS over PPC induced a slight increase of non-painful phantom sensations. Tests for significance confirm these observations, but must be interpreted with caution because of the small sample size. In conclusion, non-painful phantom sensations may be associated to a hyperexcitability of PPC and to a lesser extent of S1, which can be normalized by inhibitory rTMS. Our preliminary findings provide further evidence that neuromodulatory techniques are able to reverse phantom sensations not only after limb amputation but also in other conditions characterized by deafferentation such as SCI.

Chronic pain and the thoracic spine

In recent years there has been an increased interest in pain neuroscience in physical therapy.1,2 Emerging pain neuroscience research has challenged prevailing models used to understand and treat pain, including the Cartesian model of pain and the pain gate.2-4 Focus has shifted to the brain's processing of a pain experience, the pain neuromatrix and more recently, cortical reorganisation of body maps.2,3,5,6 In turn, these emerging theories have catapulted new treatments, such as therapeutic neuroscience education (TNE)7-10 and graded motor imagery (GMI),11,12 to the forefront of treating people suffering from persistent spinal pain. In line with their increased use, both of these approaches have exponentially gathered increasing evidence to support their use.4,10 For example, various randomised controlled trials and systematic reviews have shown that teaching patients more about the biology and physiology of their pain experience leads to positive changes in pain, pain catastrophization, function, physical movement and healthcare utilisation.7-10 Graded motor imagery, in turn, has shown increasing evidence to help pain and disability in complex pain states such as complex regional pain syndrome (CRPS).11,12 Most research using TNE and GMI has focussed on chronic low back pain (CLBP) and CRPS and none of these advanced pain treatments have been trialled on the thoracic spine. This lack of research and writings in regards to the thoracic spine is not unique to pain science, but also in manual therapy. There are, however, very unique pain neuroscience issues that skilled manual therapists may find clinically meaningful when treating a patient struggling with persistent thoracic pain. Utilising the latest understanding of pain neuroscience, three key clinical chronic thoracic issues will be discussed - hypersensitisation of intercostal nerves, posterior primary rami nerves mimicking Cloward areas and mechanical and sensitisation issues of the spinal dura in the thoracic spine.

Organisation of the motor cortex differs between people with and without knee osteoarthritis

Introduction

The aim of this study was to investigate possible differences in the organisation of the motor cortex in people with knee osteoarthritis (OA) and whether there is an association between cortical organisation and accuracy of a motor task.

Methods

fMRI data were collected while 11 participants with moderate/severe right knee OA (6 male, 69 ± 6 (mean ± SD) years) and seven asymptomatic controls (5 male, 64 ± 6 years) performed three visually guided, variable force, force matching motor tasks involving isolated isometric muscle contractions of: 1) quadriceps (knee), 2) tibialis anterior (ankle) and, 3) finger/thumb flexor (hand) muscles. fMRI data were used to map the loci of peak activation in the motor cortex during the three tasks and to assess whether there were differences in the organisation of the motor cortex between the groups for the three motor tasks. Root mean square of the difference between target and generated forces during muscle contraction quantified task accuracy.

Results

A 4.1 mm anterior shift in the representation of the knee (p = 0.03) and swap of the relative position of the knee and ankle representations in the motor cortex (p = 0.003) were found in people with knee OA. Poorer performance of the knee task was associated with more anterior placement of motor cortex loci in people with (p = 0.05) and without (p = 0.02) knee OA.

Conclusions

Differences in the organisation of the motor cortex in knee OA was demonstrated in relation to performance of knee and ankle motor tasks and was related to quality of performance of the knee motor task. These results highlight the possible mechanistic link between cortical changes and modified motor behavior in people with knee OA.

Hyperacusis following unilateral damage to the insular cortex: a three-case report

The insula is a multisensory area involved in various brain functions, including central auditory processing. However, its specific role in auditory function remains unclear. Here we report three cases of persistent hypersensitivity to auditory stimuli following damage to the insular cortex, using behavioral and neurophysiological measures. Two patients who complained of auditory disturbance since they suffered an isolated unilateral insular stroke, and one epileptic patient who underwent right insular resection for control of drug-resistant seizures, were involved in this study. These patients, all young adult women, were tested for auditory function more than one year after brain injury, and were compared to 10 healthy control participants matched for age, sex, and education. The assessment included pure-tone detection and speech detection in quiet, loudness discomfort levels, random gap detection, recognition of frequency and duration patterns, binaural separation, dichotic listening, as well as late-latency auditory event-related potentials (ERPs). Each patient showed mild or moderate hyperacusis, as revealed by decreased loudness discomfort levels, which was more important on the side of lesion in two cases. Tests of temporal processing also revealed impairments, in concordance with previous findings. ERPs of two patients were characterised by increased amplitude of the P3b component elicited during a two-tone auditory oddball detection task. This study is the first to report cases of persistent hyperacusis following damage to the insular cortex, and suggests that the insula is involved in modulating the perceived intensity of the incoming auditory stimuli during late-stage processing.

Central gain control in tinnitus and hyperacusis

Sensorineural hearing loss induced by noise or ototoxic drug exposure reduces the neural activity transmitted from the cochlea to the central auditory system. Despite a reduced cochlear output, neural activity from more central auditory structures is paradoxically enhanced at suprathreshold intensities. This compensatory increase in the central auditory activity in response to the loss of sensory input is referred to as central gain enhancement. Enhanced central gain is hypothesized to be a potential mechanism that gives rise to hyperacusis and tinnitus, two debilitating auditory perceptual disorders that afflict millions of individuals. This review will examine the evidence for gain enhancement in the central auditory system in response to cochlear damage. Further, it will address the potential cellular and molecular mechanisms underlying this enhancement and discuss the contribution of central gain enhancement to tinnitus and hyperacusis. Current evidence suggests that multiple mechanisms with distinct temporal and spectral profiles are likely to contribute to central gain enhancement. Dissecting the contributions of these different mechanisms at different levels of the central auditory system is essential for elucidating the role of central gain enhancement in tinnitus and hyperacusis and, most importantly, the development of novel treatments for these disorders.

The functional significance of cortical reorganization and the parallel development of CI therapy

For the nineteenth and the better part of the twentieth centuries two correlative beliefs were strongly held by almost all neuroscientists and practitioners in the field of neurorehabilitation. The first was that after maturity the adult CNS was hardwired and fixed, and second that in the chronic phase after CNS injury no substantial recovery of function could take place no matter what intervention was employed. However, in the last part of the twentieth century evidence began to accumulate that neither belief was correct. First, in the 1960s and 1970s, in research with primates given a surgical abolition of somatic sensation from a single forelimb, which rendered the extremity useless, it was found that behavioral techniques could convert the limb into an extremity that could be used extensively. Beginning in the late 1980s, the techniques employed with deafferented monkeys were translated into a rehabilitation treatment, termed Constraint Induced Movement therapy or CI therapy, for substantially improving the motor deficit in humans of the upper and lower extremities in the chronic phase after stroke. CI therapy has been applied successfully to other types of damage to the CNS such as traumatic brain injury, cerebral palsy, multiple sclerosis, and spinal cord injury, and it has also been used to improve function in focal hand dystonia and for aphasia after stroke. As this work was proceeding, it was being shown during the 1980s and 1990s that sustained modulation of afferent input could alter the structure of the CNS and that this topographic reorganization could have relevance to the function of the individual. The alteration in these once fundamental beliefs has given rise to important recent developments in neuroscience and neurorehabilitation and holds promise for further increasing our understanding of CNS function and extending the boundaries of what is possible in neurorehabilitation.

The reactivation of somatosensory cortex and behavioral recovery after sensory loss in mature primates

In our experiments, we removed a major source of activation of somatosensory cortex in mature monkeys by unilaterally sectioning the sensory afferents in the dorsal columns of the spinal cord at a high cervical level. At this level, the ascending branches of tactile afferents from the hand are cut, while other branches of these afferents remain intact to terminate on neurons in the dorsal horn of the spinal cord. Immediately after such a lesion, the monkeys seem relatively unimpaired in locomotion and often use the forelimb, but further inspection reveals that they prefer to use the unaffected hand in reaching for food. In addition, systematic testing indicates that they make more errors in retrieving pieces of food, and start using visual inspection of the rotated hand to confirm the success of the grasping of the food. Such difficulties are not surprising as a complete dorsal column lesion totally deactivates the contralateral hand representation in primary somatosensory cortex (area 3b). However, hand use rapidly improves over the first post-lesion weeks, and much of the hand representational territory in contralateral area 3b is reactivated by inputs from the hand in roughly a normal somatotopic pattern. Quantitative measures of single neuron response properties reveal that reactivated neurons respond to tactile stimulation on the hand with high firing rates and only slightly longer latencies. We conclude that preserved dorsal column afferents after nearly complete lesions contribute to the reactivation of cortex and the recovery of the behavior, but second-order sensory pathways in the spinal cord may also play an important role. Our microelectrode recordings indicate that these preserved first-order, and second-order pathways are initially weak and largely ineffective in activating cortex, but they are potentiated during the recovery process. Therapies that would promote this potentiation could usefully enhance recovery after spinal cord injury.

Cortical reorganization after macroreplantation at the upper extremity: a magnetoencephalographic study

With the development of microsurgical techniques, replantation has become a feasible alternative to stump treatment after the amputation of an extremity. It is known that amputation often induces phantom limb pain and cortical reorganization within the corresponding somatosensory areas. However, whether replantation reduces the risk of comparable persisting pain phenomena as well as reorganization of the primary somatosensory cortex is still widely unknown. Therefore, the present study aimed to investigate the potential development of persistent pain and cortical reorganization of the hand and lip areas within the sensory cortex by means of magnetoencephalographic dipole analyses after replantation of a traumatically amputated upper limb proximal to the radiocarpal joint. Cortical reorganization was investigated in 13 patients with limb replantation using air puff stimulation of the phalanges of both thumbs and both corners of the lower lip. Displacement of the centre of gravity of lip and thumb representations and increased cortical activity were found in the limb and face areas of the primary somatosensory cortex contralateral to the replanted arm when compared to the ipsilateral hemisphere. Thus, cortical reorganization in the primary somatosensory cortex also occurs after replantation of the upper extremity. Patients' reports of pain in the replanted body part were negatively correlated with the amount of cortical reorganization, i.e. the more pain the patients reported, the less reorganization of the subjects' hand representation within the primary somatosensory cortex was observed. Longitudinal studies in patients after macroreplantation are necessary to assess whether the observed reorganization in the primary somatosensory cortex is a result of changes within the representation of the replanted arm and/or neighbouring representations and to assess the relationship between the development of persistent pain and reorganization.

Phantom limb pain: a systematic neuroanatomical-based review of pharmacologic treatment

OBJECTIVE

Review the current evidence-based pharmacotherapy for phantom limb pain (PLP) in the context of the current understanding of the pathophysiology of this condition.

DESIGN

We conducted a systematic review of original research papers specifically investigating the pharmacologic treatment of PLP. Literature was sourced from PubMed, Embase, Scopus, and the Cochrane Central Register of Controlled Trials (CENTRAL). Studies with animals, "neuropathic" but not "phantom limb" pain, or without pain scores and/or functional measures as primary outcomes were excluded. A level of evidence 1-4 was ascribed to individual treatments. These levels included meta-analysis or systematic reviews (level 1), one or more well-powered randomized, controlled trials (level 2), retrospective studies, open-label trials, pilot studies (level 3), and anecdotes, case reports, or clinical experience (level 4).

RESULTS

We found level 2 evidence for gabapentin, both oral (PO) and intravenous (IV) morphine, tramadol, intramuscular (IM) botulinum toxin, IV and epidural Ketamine, level 3 evidence for amitriptyline, dextromethorphan, topiramate, IV calcitonin, PO memantine, continuous perineural catheter analgesia with ropivacaine, and level 4 evidence for methadone, intrathecal (IT) buprenorphine, IT and epidural fentanyl, duloxetine, fluoxetine, mirtazapine, clonazepam, milnacipran, capsaicin, and pregabalin.

CONCLUSIONS

Currently, the best evidence (level 2) exists for the use of IV ketamine and IV morphine for the short-term perioperative treatment of PLP and PO morphine for an intermediate to long-term treatment effect (8 weeks to 1 year). Level 2 evidence is mixed for the efficacy of perioperative epidural anesthesia with morphine and bupivacaine for short to long-term pain relief (perioperatively up to 1 year) as well as for the use of gabapentin for pain relief of intermediate duration (6 weeks).

Motor and parietal cortex stimulation for phantom limb pain and sensations

Limb amputation may lead to chronic painful sensations referred to the absent limb, ie phantom limb pain (PLP), which is likely subtended by maladaptive plasticity. The present study investigated whether transcranial direct current stimulation (tDCS), a noninvasive technique of brain stimulation that can modulate neuroplasticity, can reduce PLP. In 2 double-blind, sham-controlled experiments in subjects with unilateral lower or upper limb amputation, we measured the effects of a single session of tDCS (2 mA, 15 min) of the primary motor cortex (M1) and of the posterior parietal cortex (PPC) on PLP, stump pain, nonpainful phantom limb sensations and telescoping. Anodal tDCS of M1 induced a selective short-lasting decrease of PLP, whereas cathodal tDCS of PPC induced a selective short-lasting decrease of nonpainful phantom sensations; stump pain and telescoping were not affected by parietal or by motor tDCS. These findings demonstrate that painful and nonpainful phantom limb sensations are dissociable phenomena. PLP is associated primarily with cortical excitability shifts in the sensorimotor network; increasing excitability in this system by anodal tDCS has an antalgic effect on PLP. Conversely, nonpainful phantom sensations are associated to a hyperexcitation of PPC that can be normalized by cathodal tDCS. This evidence highlights the relationship between the level of excitability of different cortical areas, which underpins maladaptive plasticity following limb amputation and the phenomenology of phantom limb, and it opens up new opportunities for the use of tDCS in the treatment of PLP.

Pain and neurological sequelae of cluster munitions on children and adolescents in South Lebanon

This paper aims at evaluating the neurological repercussions arising from injuries sustained due to cluster munitions in children up to 18 years in South Lebanon following the 2006 conflict. Data on neurological and pain symptoms suffered during and after treatment because of sub-munitions in South Lebanon from August 2006 till late 2011 were prospectively recorded. Patients were divided into subcategories; children aged 12 and under and adolescents aged between 13 and 18. During the study period, there were 407 casualties, 122 (30%) of which were aged 18 years or younger. There were 116 (95%) males and six (5%) females. Average age was 14 years. 10 (8.2%), all males, died as a result of their injuries. 42 (34.4%) were children and 80 (65.6%) were adolescents. 112 had surgical treatments for their injuries. 83 out of 112 patients (74%) with non-lethal injuries had amputations, 67% children and 78% adolescents. Among those who had amputations, 31 (37.4%) suffered from phantom limb pain and 71% suffered from stump/residual limb pain. 88% of patients were diagnosed with post-traumatic stress disorder (44% children and 77% adolescents) and 41% were diagnosed with post-concussion syndrome. Four patients (3.6%) suffered from traumatic brain injuries, both penetrating and closed. Pain syndromes were found in all patients who had amputation. The injury related comorbidities together with many post-concussion syndrome cases, and fewer traumatic brain injuries lead into a high level of physical, psychosocial and economic burdens on the community.

Reappraisal of the somatosensory homunculus and its discontinuities

Neuroscience folklore has it that somatotopy in human primary somatosensory cortex (SI) has two significant discontinuities: the hands and face map onto adjacent regions in SI, as do the feet and genitalia. It has been proposed that these conjunctions in SI result from coincident sources of stimulation in the fetal position, where the hands frequently touch the face, and the feet the genitalia. Computer modeling using a Hebbian variant of the self-organizing Kohonen net is consistent with this proposal. However, recent work reveals that the genital representation in SI for cutaneous sensations (as opposed to tumescence) is continuous with that of the lower trunk and thigh. This result, in conjunction with reports of separate face innervation and its earlier onset of sensory function, compared to that of the rest of the body, allows a reappraisal of homuncular organization. It is proposed that the somatosensory homunculus comprises two distinct somatotopic regions: the face representation and that of the rest of the body. Principles of self-organization do not account satisfactorily for the overall homuncular map. These results may serve to alert computational modelers that intrinsic developmental factors can override simple rules of plasticity.

Functional expansion of sensorimotor representation and structural reorganization of callosal connections in lower limb amputees

Previous studies have indicated that amputation or deafferentation of a limb induces functional changes in sensory (S1) and motor (M1) cortices, related to phantom limb pain. However, the extent of cortical reorganization after lower limb amputation in patients with nonpainful phantom phenomena remains uncertain. In this study, we combined functional magnetic resonance (fMRI) and diffusion tensor imaging (DTI) to investigate the existence and extent of cortical and callosal plasticity in these subjects. Nine "painless" patients with lower limb amputation and nine control subjects (sex- and age-matched) underwent a 3-T MRI protocol, including fMRI with somatosensory stimulation. In amputees, we observed an expansion of activation maps of the stump in S1 and M1 of the deafferented hemisphere, spreading to neighboring regions that represent the trunk and upper limbs. We also observed that tactile stimulation of the intact foot in amputees induced a greater activation of ipsilateral S1, when compared with controls. These results demonstrate a functional remapping of S1 in lower limb amputees. However, in contrast to previous studies, these neuroplastic changes do not appear to be dependent on phantom pain but do also occur in those who reported only the presence of phantom sensation without pain. In addition, our findings indicate that amputation of a limb also induces changes in the cortical representation of the intact limb. Finally, DTI analysis showed structural changes in the corpus callosum of amputees, compatible with the hypothesis that phantom sensations may depend on inhibitory release in the sensorimotor cortex.

Long-term antalgic effects of repetitive transcranial magnetic stimulation of motor cortex and serum beta-endorphin in patients with phantom pain

OBJECTIVES

To assess the long-term analgesic effect of repetitive transcranial stimulation (rTMS) on chronic phantom pain using high frequency stimulation and to measure the serum beta-endorphin level pre- and post-rTMS.

MATERIAL AND METHODS

The study included 27 patients with unilateral amputation; all patients had chronic phantom pain. The patients were classified into two groups. Seventeen patients received 10 minutes real rTMS over the hand area of motor cortex (20 Hz, 10 second trains, intensity 80% of motor threshold) every day for five consecutive days and 10 patients received sham stimulation. Pain was assessed using a visual analogue scale (VAS) and the Leeds assessment of neuropathic symptoms and signs (LANSS) scale, before and after the first, fifth sessions, one and two months after the last session. Quantitative determination of serum beta-endorphin before and after five sessions was measured.

RESULTS

There was no significant difference between true and sham groups in the duration of illness, VAS, LANSS scores and resting motor threshold in upper and lower limb amputation at the base line. VAS and LANS scores of the patients who received real rTMS decreased more over the course of the treatment through the different points of follow-up (after five sessions, one and two months) than those who received sham stimulation. Serum beta-endorphin was increased significantly after real stimulation with no changes in patients received shame. Serum beta-endorphin showed no significant correlation to Hamilton depression, anxiety, VAS and LANS scores in true or sham groups before or after five sessions for rTMS.

CONCLUSION

These results confirm that five daily sessions of rTMS over motor cortex can produce long lasting pain relief in patients with phantom pain and it might be related to an elevation of serum beta-endorphin concentration.

A randomized controlled study to evaluate the efficacy of noninvasive limb cover for chronic phantom limb pain among veteran amputees

OBJECTIVE

To assess the efficacy of a noninvasive limb cover for treating chronic phantom limb pain (PLP).

DESIGN

Randomized, double-blind, placebo-controlled trial.

SETTING

Outpatient clinic.

PARTICIPANTS

We randomly assigned 57 subjects to 2 groups: true noninvasive limb cover (n=30) and sham noninvasive limb cover (n=27). Inclusion criteria included age of 18 years or greater, upper or lower extremity amputation with healed residual limb, and 3 or more episodes of PLP during the previous 6 weeks.

INTERVENTIONS

Subjects received 2 true or sham noninvasive limb covers to be worn over the prosthesis and residual limbs 24 hours a day for 12 weeks.

MAIN OUTCOME MEASURES

Primary outcome measure was the numerical pain rating scale of PLP level (0-10). Secondary outcomes included overall pain level (0-10), PLP frequency per week, and the Veterans RAND 12-Item Health Survey (VR-12). We collected data at baseline and at 6- and 12-week follow-up visits.

RESULTS

Demographic and clinical characteristics were not significantly different between groups. The true noninvasive limb cover group reported nonsignificant reductions in PLP from 5.9±1.9 at baseline to 3.9±1.7 at the 12-week follow-up. The sham noninvasive limb cover group also had nonsignificant reducations in PLP from 6.5±1.8 to 4.2±2.3. PLP did not differ significantly between the 2 groups at 6 weeks (mean difference, 0.8; 95% confidence interval [CI], -1.4 to 3) or at 12 weeks (mean difference, 0.2; 95% CI, -1.9 to 2.3). Similarly, overall pain level, PLP episodes per week, and VR-12 physical and mental health component scores did not differ between the 2 groups at 6 and 12 weeks.

CONCLUSIONS

A true noninvasive limb cover did not significantly decrease PLP levels or the frequency of PLP episodes per week, overall bodily pain levels, or VR-12 physical and mental health component scores compared with a sham noninvasive limb cover in our veteran amputee sample.

Prevention of chronic pain after surgical nerve injury: amputation and thoracotomy

Although techniques for acute pain management have improved in recent years, a dramatic reduction in the incidence and severity of chronic pain following surgery has not occurred. Amputation and thoracotomy, although technically different, share the commonalities of unavoidable nerve injury and the frequent presence of persistent postsurgical neuropathic pain. The authors review the risk factors for the development of chronic pain following these surgeries and the current evidence that supports analgesic interventions. The inconclusive results from many preemptive analgesic studies may require us to reconceptualize the perioperative treatment period as a time of gradual neurologic remodeling.

Evaluation of a noninvasive command scheme for upper-limb prostheses in a virtual reality reach and grasp task

C5/C6 tetraplegic patients and transhumeral amputees may be able to use voluntary shoulder motion as command signals for a functional electrical stimulation system or transhumeral prosthesis. Stereotyped relationships, termed "postural synergies," among the shoulder, forearm, and wrist joints emerge during goal-oriented reaching and transport movements as performed by able-bodied subjects. Thus, the posture of the shoulder can potentially be used to infer the desired posture of the elbow and forearm joints during reaching and transporting movements. We investigated how well able-bodied subjects could learn to use a noninvasive command scheme based on inferences from these postural synergies to control a simulated transhumeral prosthesis in a virtual reality task. We compared the performance of subjects using the inferential command scheme (ICS) with subjects operating the simulated prosthesis in virtual reality according to complete motion tracking of their actual arm and hand movements. Initially, subjects performed poorly with the ICS but improved rapidly with modest amounts of practice, eventually achieving performance only slightly less than subjects using complete motion tracking. Thus, inferring the desired movement of distal joints from voluntary shoulder movements appears to be an intuitive and noninvasive approach for obtaining command signals for prostheses to restore reaching and grasping functions.

Pattern recognition control of multifunction myoelectric prostheses by patients with congenital transradial limb defects: a preliminary study

BACKGROUND

Electromyography (EMG) pattern recognition offers the potential for improved control of multifunction myoelectric prostheses. However, it is unclear whether this technology can be successfully used by congenital amputees.

OBJECTIVE

The purpose of this investigation was to assess the ability of congenital transradial amputees to control a virtual multifunction prosthesis using EMG pattern recognition and compare their performance to that of acquired amputees from a previous study.

STUDY DESIGN

Preliminary cross-sectional study.

METHODS

Four congenital transradial amputees trained and tested a linear discriminant analysis (LDA) classifier with four wrist movements, five hand movements, and a no-movement class. Subjects then tested the classifier in real time using a virtual arm.

RESULTS

Performance metrics for the residual limb were poorer than those with the intact limb (classification accuracy: 52.1% ± 15.0% vs. 93.2% ± 15.8%; motion-completion rate: 49.0%± 23.0% vs. 84.0% ± 9.4%; motion-completion time: 2.05 ± 0.75 s vs. 1.13 ± 0.05 s, respectively). On average, performance with the residual limb by congenital amputees was reduced compared to that reported for acquired transradial amputees. However, one subject performed similarly to acquired amputees.

CONCLUSIONS

Pattern recognition control may be a viable option for some congenital amputees. Further study is warranted to determine success factors.

Short and intense tailor-made notched music training against tinnitus: the tinnitus frequency matters

Tinnitus is one of the most common diseases in industrialized countries. Here, we developed and evaluated a short-term (5 subsequent days) and intensive (6 hours/day) tailor-made notched music training (TMNMT) for patients suffering from chronic, tonal tinnitus. We evaluated (i) the TMNMT efficacy in terms of behavioral and magnetoencephalographic outcome measures for two matched patient groups with either low (≤8 kHz, N = 10) or high (>8 kHz, N = 10) tinnitus frequencies, and the (ii) persistency of the TMNMT effects over the course of a four weeks post-training phase. The results indicated that the short-term intensive TMNMT took effect in patients with tinnitus frequencies ≤8 kHz: subjective tinnitus loudness, tinnitus-related distress, and tinnitus-related auditory cortex evoked activity were significantly reduced after TMNMT completion. However, in the patients with tinnitus frequencies >8 kHz, significant changes were not observed. Interpreted in their entirety, the results also indicated that the induced changes in auditory cortex evoked neuronal activity and tinnitus loudness were not persistent, encouraging the application of the TMNMT as a longer-term training. The findings are essential in guiding the intended transfer of this neuro-scientific treatment approach into routine clinical practice.

Motor cortex representation of the upper-limb in individuals born without a hand

The body schema is an action-related representation of the body that arises from activity in a network of multiple brain areas. While it was initially thought that the body schema developed with experience, the existence of phantom limbs in individuals born without a limb (amelics) led to the suggestion that it was innate. The problem with this idea, however, is that the vast majority of amelics do not report the presence of a phantom limb. Transcranial magnetic stimulation (TMS) applied over the primary motor cortex (M1) of traumatic amputees can evoke movement sensations in the phantom, suggesting that traumatic amputation does not delete movement representations of the missing hand. Given this, we asked whether the absence of a phantom limb in the majority of amelics means that the motor cortex does not contain a cortical representation of the missing limb, or whether it is present but has been deactivated by the lack of sensorimotor experience. In four upper-limb amelic subjects we directly stimulated the arm/hand region of M1 to see 1) whether we could evoke phantom sensations, and 2) whether muscle representations in the two cortices were organised asymmetrically. TMS applied over the motor cortex contralateral to the missing limb evoked contractions in stump muscles but did not evoke phantom movement sensations. The location and extent of muscle maps varied between hemispheres but did not reveal any systematic asymmetries. In contrast, forearm muscle thresholds were always higher for the missing limb side. We suggest that phantom movement sensations reported by some upper limb amelics are mostly driven by vision and not by the persistence of motor commands to the missing limb within the sensorimotor cortex. We propose that prewired movement representations of a limb need the experience of movement to be expressed within the primary motor cortex.

The menacing phantom: what pulls the trigger?

Phantom phenomena are frequent following amputation, but how this often painful experience is modified or triggered by spontaneous events or sensations often puzzles amputees and clinicians alike. We explored triggers of phantom phenomena in a heterogeneous sample of 264 upper and lower limb adult amputees with phantom sensations. Participants completed a structured questionnaire to determine the prevalence and nature of the triggers of phantom phenomena. The four categories of triggers identified include: (a) a quarter of participants experiencing psychological, emotional or autonomic triggers; (b) half experiencing behavioral triggers, "forgetting" the limb's absence and attempting to use the phantom; (c) one-fifth experiencing weather-induced triggers; and (d) one-third experiencing sensations referred from parts of the body. Upper limb amputees; and were more likely to experience weather-induced phantom phenomena than lower limb amputees; and upper and lower limb amputees were equally likely to experience referred sensations from the genitals, contradicting the homuncular remapping hypothesis. Traumatic amputees were more likely to report emotional triggers. Further, while those with emotional triggers exhibited poorer acceptance of the limitations of amputation, they were more likely to employ adaptive coping mechanisms. Finally, habitual "forgetting" behaviors were most common soon after amputation, whereas other more adaptive schemata (e.g., self-defense) were equally likely to be performed at any time following amputation. Various likely inter-related mechanisms are discussed in relation to phantom triggers. Ultimately, optimizing stump and neuroma management, as well as restoring function of central networks for pain, limb movement, and amputation-related memories, should help manage spontaneously triggered phantom phenomena.

Demonstration of motor imagery movement and phantom movement-related neuronal activity in human thalamus

Functional imaging studies show that motor imagery activates multiple structures in the human forebrain. We now show that phantom movements in an amputee and imagined movements in intact individuals elicit responses from neurons in several human thalamic nuclei. These include the somatic sensory nucleus receiving input from the periphery (ventral caudal), and the motor nuclei receiving input from the cerebellum [ventral intermediate (Vim)] and the basal ganglia [ventral oral posterior (Vop)]. Seven neurons in the amputee showed phantom movement-related activity (three Vim, two Vop, and two ventral caudal). In addition, seven neurons in a group of three controls showed motor imagery-related activity (four Vim and three Vop). These studies were performed during single neuron recording sessions in patients undergoing therapeutic treatment of phantom pain, tremor, and chronic pain conditions by thalamic stimulation. The activity of neurons in these sensory and motor nuclei, respectively, may encode the expected sensory consequences and the dynamics of planned movements.

Robotic touch shifts perception of embodiment to a prosthesis in targeted reinnervation amputees

Existing prosthetic limbs do not provide amputees with cutaneous feedback. Tactile feedback is essential to intuitive control of a prosthetic limb and it is now clear that the sense of body self-identification is also linked to cutaneous touch. Here we have created an artificial sense of touch for a prosthetic limb by coupling a pressure sensor on the hand through a robotic stimulator to surgically redirected cutaneous sensory nerves (targeted reinnervation) that once served the lost limb. We hypothesize that providing physiologically relevant cutaneous touch feedback may help an amputee incorporate an artificial limb into his or her self image. To investigate this we used a robotic touch interface coupled with a prosthetic limb and tested it with two targeted reinnervation amputees in a series of experiments fashioned after the Rubber Hand Illusion. Results from both subjective (self-reported) and objective (physiological) measures of embodiment (questionnaires, psychophysical temporal order judgements and residual limb temperature measurements) indicate that returning physiologically appropriate cutaneous feedback from a prosthetic limb drives a perceptual shift towards embodiment of the device for these amputees. Measurements provide evidence that the illusion created is vivid. We suggest that this may help amputees to more effectively incorporate an artificial limb into their self image, providing the possibility that a prosthesis becomes not only a tool, but also an integrated body part.

Cortical representation of the human hand assessed by two levels of high-resolution EEG recordings

Increasing interest in cortical plasticity has prompted the growing use of somatosensory evoked potentials (SEPs) to estimate changes in the cortical representation of body regions. Here, we tested the effect of different sites of hand stimulation and of the density of spatial sampling in the quality of estimation of somatosensory sources. Sources of two SEP components from the primary somatosensory cortex (N20/P20 and P45) were estimated using two levels of spatial sampling (64- vs. 128-channel) and stimulation of four distal sites in the upper limbs, including single digits (first vs. fifth) and distal nerves with comparable cortical projection (superficial branch of the radial nerve and distal ulnar nerve). The most robust separation of somatosensory sources was achieved by comparing the cortical representations of the first digit and the distal ulnar nerve territories on the N20/P20 component of SEPs. Although both the 64- and the 128-electrode montages correctly discriminated these two areas, only the 128-electrode montage was able to significantly separate sources in the other cases, notably when using first versus fifth digit stimulation. Trustworthy distinction of cortical representations was not obtainable when using the P45 component, probably because of greater activation volume, radial orientation of sources in areas 1-2 and increased variability with attention and vigilance. Assessment of tangential SEP components to stimulation of first digit versus ulnar nerve appears the best option to assess plastic somatosensory changes, especially when using relatively low-electrode sampling.

Adaptation and maladaptation insights from brain plasticity

Evolutionary concepts such as adaptation and maladaptation have been used by neuroscientists to explain brain properties and mechanisms. In particular, one of the most compelling characteristics of the brain, known as neuroplasticity, denotes the ability of the brain to continuously adapt its functional and structural organization to changing requirements. Although brain plasticity has evolved to favor adaptation, there are cases in which the same mechanisms underlying adaptive plasticity can turn into maladaptive changes. Here, we will consider brain plasticity and its functional and structural consequences from an evolutionary perspective, discussing cases of adaptive and maladaptive plasticity and using examples from typical and atypical development.

Amputation with median nerve redirection (targeted reinnervation) reactivates forepaw barrel subfield in rats

Prosthetic limbs are difficult to control and do not provide sensory feedback. Targeted reinnervation was developed as a neural-machine interface for amputees to address these issues. In targeted reinnervation, amputated nerves are redirected to proximal muscles and skin, creating nerve interfaces for prosthesis control and sensory feedback. Touching the reinnervated skin causes sensation to be projected to the missing limb. Here we use electrophysiological brain recording in the Sprague Dawley rat to investigate the changes to somatosensory cortex (S1) following amputation and nerve redirection with the intent to provide insight into the sensory phenomena observed in human targeted reinnervation amputees. Recordings revealed that redirected nerves established an expanded representation in S1, which may help to explain the projected sensations that encompass large areas of the hand in targeted reinnervation amputees. These results also provide evidence that the reinnervated target skin could serve as a line of communication from a prosthesis to cortical hand processing regions. S1 border regions were simultaneously responsive to reinnervated input and also vibrissae, lower lip, and hindfoot, suggesting competition for deactivated cortical territory. Electrically evoked potential latencies from reinnervated skin to cortex suggest direct connection of the redirected afferents to the forepaw processing region of S1. Latencies also provide evidence that the widespread reactivation of S1 cortex may arise from central anatomical interconnectivity. Targeted reinnervation offers the opportunity to examine the cortical plasticity effects when behaviorally important sensory afferents are redirected from their original location to a new skin surface on a different part of the body.

Event-Related Functional Magnetic Resonance Images during the Perception of Phantom Limb. A Brushing Task

The phantom limb phenomenon has been used in amputee patients as a paradigm to study plasticity, mainly of the sensorimotor cortex. Nevertheless, most functional studies have been done in upper limb amputee patients using magnetoencephalography and functional magnetic resonance image imaging (fMRI). In addition, the actual experience of phantom limb sensation has not been widely used to study the neural mechanism of the human brain as a conscious knowledge of the phantom limb perception like the integration of the body image in amputee patients. fMRI studies of patients with lower limb amputation have recently been published, but none of these used an event-related design to try to observe only the stimulus application, correlating images with the subject's indication of phantom perception and discarding images with no phantom perception. In this work, we used the event-related fMRI design in two right-handed patients with identical right, transfemoral amputations, performing the same sensitive stimulation in a 3.0 T MR scanner. For comparison, we applied the same paradigm to six control subjects to compare the resulting functional maps. We found areas with statistical significance in the sensorimotor cortex contralateral to the site of stimulation, in the parietal lobe in Brodmann areas 3 in both cases (Patients and Control Subjects), but we also found activation in the Brodmann areas 6, 40, and 5 with stimulation of the stump. We observed a specific activation of the frontoparietal circuit during phantom limb perception in both amputee patients.

Abnormal functioning of the thalamocortical system underlies the conscious awareness of the phantom limb phenomenon

Phantom limb (PL), a phenomenon experienced by most patients after amputation, has mostly served as a paradigm to study experiences that appear to be associated with neural plasticity within the CNS. However, the subjective nature of PL experiences has had no definitive means of reliable assessment other than using patients' direct reports, nor was there a way to study the neural mechanisms involved in the conscious awareness of this mental phenomenon. Here we obtained patients' indirect responses to PL experiences for an objective evaluation using functional magnetic resonance imaging (fMRI). Six control subjects and six lower limb (LL) amputees participated in a motor imagery task for both the intact and the particular phantom toes. While all subjects shared neural processing of distinctive regional cerebral activations during motor imagery of the intact toes (prefrontal (PF), supplementary motor area (SMA), primary motor cortex (M1), superior temporal gyrus (STG)), it was only during motor imagery of the amputated toes in amputees that we observed an increased blood oxygen level-dependent (BOLD) signal in the contralateral basal ganglia at the medial globus pallidus (MGP), substantia nigra (SN), and thalamus. This increased BOLD signal in the basal ganglia-thalamus-cortex pathway during imaginary movement of the phantom toes may reflect an abnormal open loop functioning of the thalamocortical system underlying the conscious awareness of the phantom phenomenon. We suggest that the reduction in afferent information contributes to and coalesces with the higher-level reorganization resulting in the subjective conscious awareness of the phantom limb.

Cross-modal plasticity in the human thalamus: evidence from intraoperative macrostimulations

During stereotactic functional neurosurgery, stimulation procedure to control for proper target localization provides a unique opportunity to investigate pathophysiological phenomena that cannot be addressed in experimental setups. Here we report on the distribution of response modalities to 487 intraoperative thalamic stimulations performed in 24 neurogenic pain (NP), 17 parkinsonian (PD) and 10 neuropsychiatric (Npsy) patients. Threshold responses were subdivided into somatosensory, motor and affective, and compared between medial (central lateral nucleus) and lateral (ventral anterior, ventral lateral and ventral medial) thalamic nuclei and between patients groups. Major findings were as follows: in the medial thalamus, evoked responses were for a large majority (95%) somatosensory in NP patients, 47% were motor in PD patients, and 54% affective in Npsy patients. In the lateral thalamus, a much higher proportion of somatosensory (83%) than motor responses (5%) was evoked in NP patients, while the proportion was reversed in PD patients (69% motor vs. 21% somatosensory). These results provide the first evidence for functional cross-modal changes in lateral and medial thalamic nuclei in response to intraoperative stimulations in different functional disorders. This extensive functional reorganization sheds new light on wide-range plasticity in the adult human thalamocortical system.

Metal bar prevents phantom limb motion: case study of an amputation patient who showed a profound change in the awareness of his phantom limb

This case report describes an amputee (patient A.S., a 60-year-old male forelimb amputee) who had an extraordinary experience with a phantom limb. He complained that he could not move the wrist of his phantom limb because a metal bar was perceived to be grasped by the hand. As a solution for removing the metal bar, we invited the patient to undergo mirror reflection-induced visual feedback therapy. The patient reported that the metal bar previously grasped by his hand was successfully removed from the phantom during the course of therapy. Interestingly, this experience was accompanied by profound changes in the EMG modulation in the residual wrist muscles. In this article, the possible mechanisms underlying this interesting phenomenon will be discussed.

Behavioral and Electrophysiological Evidence of Motor Cortex Activation Related to an Amputated Limb: A Multisensorial Approach

Phantom limb sensations may be linked to motor activities in the deafferented cortices of amputees, with artificial visual feedback of an amputated limb leading to enhanced phantom sensations. The present study was designed to verify if cortical motor activity related to an amputated limb can be triggered by visual input using an objective behavioral measure and with a neurophysiological correlate. Trauma amputees and normally limbed subjects showed superior performance in a mirror-drawing task when the mirror was placed sagittally (giving visual feedback of the amputated/inactive limb) compared with when it was placed frontally. Measurement of lateralized movement-related brain potentials showed that, under the lateral mirror condition, contralateral motor activity of the viewed hand was observed in both normal subjects and trauma amputees. In contrast, this activity was not observed in subjects with congenital limb absence. These findings suggest that, in traumatic amputees, motor enhancement due to visualization of the movements of the missing limb reflects the effectiveness of motor commands to the missing limb, strengthening the hypothesis of the functional survival of deafferented cortical motor areas.

Sensory capacity of reinnervated skin after redirection of amputated upper limb nerves to the chest

Targeted reinnervation is a new neural-machine interface that has been developed to help improve the function of new-generation prosthetic limbs. Targeted reinnervation is a surgical procedure that takes the nerves that once innervated a severed limb and redirects them to proximal muscle and skin sites. The sensory afferents of the redirected nerves reinnervate the skin overlying the transfer site. This creates a sensory expression of the missing limb in the amputee's reinnervated skin. When these individuals are touched on this reinnervated skin they feel as though they are being touched on their missing limb. Targeted reinnervation takes nerves that once served the hand, a skin region of high functional importance, and redirects them to less functionally relevant skin areas adjacent to the amputation site. In an effort to better understand the sensory capacity of the reinnervated target skin following this procedure, we examined grating orientation thresholds and point localization thresholds on two amputees who had undergone the targeted reinnervation surgery. Grating orientation thresholds and point localization thresholds were also measured on the contralateral normal skin of the targeted reinnervation amputees and on analogous sites in able-bodied controls. Grating orientation thresholds for the reinnervated skin of the targeted reinnervation amputees were found to be similar to normal ranges for both the amputees' contralateral skin and also for the control population. Point localization thresholds for these amputees were found to be lower for their reinnervated skin than for their contralateral skin. Reinnervated point localization thresholds values were also lower in comparison to homologous chest sites on the control population. Mechanisms appear to be in place to maximize re-established touch input in targeted reinnervation amputees. It seems that sound sensory function is provided to the denervated skin of the residual limb when connected to afferent pathways once serving highly functionally relevant regions of the brain. This suggests that tactile interface devices could be used to give a physiologically appropriate sense of touch to a prosthetic limb, which would likely help with better functional utilization of the prosthetic device and possibly help to more effectively integrate the device with the user's self-image.

Re-emergence of hand-muscle representations in human motor cortex after hand allograft

The human primary motor cortex (M1) undergoes considerable reorganization in response to traumatic upper limb amputation. The representations of the preserved arm muscles expand, invading portions of M1 previously dedicated to the hand, suggesting that former hand neurons are reassigned to the control of remaining proximal upper limb muscles. Hand allograft offers a unique opportunity to study the reversibility of such long-term cortical changes. We used transcranial magnetic stimulation in patient LB, who underwent bilateral hand transplantation 3 years after a traumatic amputation, to longitudinally track both the emergence of intrinsic (from the donor) hand muscles in M1 as well as changes in the representation of stump (upper arm and forearm) muscles. The same muscles were also mapped in patient CD, the first bilateral hand allograft recipient. Newly transplanted intrinsic muscles acquired a cortical representation in LB's M1 at 10 months postgraft for the left hand and at 26 months for the right hand. The appearance of a cortical representation of transplanted hand muscles in M1 coincided with the shrinkage of stump muscle representations for the left but not for the right side. In patient CD, transcranial magnetic stimulation performed at 51 months postgraft revealed a complete set of intrinsic hand-muscle representations for the left but not the right hand. Our findings show that newly transplanted muscles can be recognized and integrated into the patient's motor cortex.

Surgical treatment by electrical stimulation of the auditory cortex for intractable tinnitus

Tinnitus is a public health issue in France. Around 1% of the population is affected and 30,000 people are handicapped in their daily life. The treatments available for disabling tinnitus have until now been disappointing. We are reporting on the surgical treatment by electrical stimulation of the auditory cortex of a female patient affected by disabling tinnitus that resisted classical treatments. The tinnitus appeared suddenly 10 years ago after a left ear tympanoplasty. The acouphenometry measures revealed a bilateral tinnitus, predominant on the right side, constant, with high frequency (6000 Hz). Transcranial magnetic stimulation (TMS) was performed at first with several supraliminal and infraliminal protocols. This showed promising results. Anatomic and functional magnetic resonance imaging (fMRI) of the auditory cortex before and after repetitive TMS (rTMS) demonstrated a modification of the cortical activity and where the ideal location for a cortical electrode might be, to straddle primary and secondary auditory cortex. After these investigations, two quadra polar electrodes (Resume, Medtronic Ltd, Hertfordshire, UK), connected to a stimulating device implanted under the skin (Synergy, Medtronic Ltd), were extradurally implanted. The surgical procedure was similar to the one performed for analgesic cortical stimulation. No surgical complications were reported. The activation of the stimulator provided a reduction of 65% of the tinnitus impact, with a persistent effect on the right side. The feasibility of the cortical stimulation in symptomatic treatment of tinnitus was proven by this preparatory work. The middle- and long-term therapeutic effects remain to be evaluated.

On the use of longitudinal intrafascicular peripheral interfaces for the control of cybernetic hand prostheses in amputees

Significant strides have been recently made to develop highly sensorized cybernetic prostheses aimed at restoring sensorimotor limb functions to those who have lost them because of a traumatic event (amputation). In these cases, one of the main goals is to create a bidirectional link between the artificial devices (e.g., robotic hands, arms, or legs) and the nervous system. Several human-machine interfaces (HMIs) are currently used to this aim. Among them, interfaces with the peripheral nervous system and in particular longitudinal intrafascicular electrodes can be a promising solution able to improve the current situation. In this paper, the potentials and limits of the use of this interface to control robotic devices are presented. Specific information is provided on: 1) the neurophysiological bases for the use peripheral nerve interfaces; 2) a comparison of the potentials of the different peripheral neural interfaces; 3) the possibility of extracting and appropriately interpreting the neural code for motor commands and of delivering sensory feedback by stimulating afferent fibers by using longitudinal intrafascicular electrodes; 4) a preliminary comparative analysis of the performance of this approach with the ones of others HMIs; 5) the open issues which have to be addressed for a chronic usability of this approach.

Chapter 27: Neural plasticity after nerve injury and regeneration

Injuries to the peripheral nerves result in partial or total loss of motor, sensory, and autonomic functions in the denervated segments of the body due to the interruption of axons, degeneration of distal nerve fibers, and eventual death of axotomized neurons. Functional deficits caused by nerve injuries can be compensated by reinnervation of denervated targets by regenerating injured axons or by collateral branching of undamaged axons, and remodeling of nervous system circuitry related to the lost functions. Plasticity of central connections may compensate functionally for the lack of adequate target reinnervation; however, plasticity has limited effects on disturbed sensory localization or fine motor control after injuries, and may even result in maladaptive changes, such as neuropathic pain and hyperreflexia. After axotomy, neurons shift from a transmitter to a regenerative phenotype, activating molecular pathways that promote neuronal survival and axonal regeneration. Peripheral nerve injuries also induce a cascade of events, at the molecular, cellular, and system levels, initiated by the injury and progressing throughout plastic changes at the spinal cord, brainstem nuclei, thalamus, and brain cortex. Mechanisms involved in these changes include neurochemical changes, functional alterations of excitatory and inhibitory synaptic connections, sprouting of new connections, and reorganization of sensory and motor central maps. An important direction for research is the development of therapeutic strategies that enhance axonal regeneration, promote selective target reinnervation, and are also able to modulate central nervous system reorganization, amplifying positive adaptive changes that improve functional recovery and also reducing undesirable effects.

Cortical overlap of joint representations contributes to the loss of independent joint control following stroke

The loss of independent joint control in the paretic upper limb is a cardinal sign of movement disorders following stroke. However, the underlying neural mechanisms for such a loss following stroke are still largely unknown. In order to investigate the possible contribution of altered sensorimotor cortical activity to the loss of independent joint control, we measured electroencephalographic (EEG) and torque signals during the generation of static shoulder/elbow torques. We found significant increases in the overlap of shoulder and elbow joint representations at the cortical level in stroke subjects as compared to control subjects. Linear regression results demonstrated significant associations between the cortical overlap of joint representations and the degree of the loss of independent joint control. Therefore, we conclude that an increased overlap of cortical representations for shoulder and elbow contributes to the expression of the loss of independent shoulder/elbow control of the paretic upper limb in chronic hemiparetic stroke survivors.

Painful and nonpainful phantom and stump sensations in acute traumatic amputees

BACKGROUND

The formation, prevalence, intensity, course, and predisposing factors of phantom limb pain were investigated to determine possible mechanisms of the origin of phantom limb pain in traumatic upper limb amputees.

METHODS

Ninety-six upper limb amputees participated in the study. A questionnaire assessed the following question: side, date, extension, and cause of amputation; preamputation pain; and presence or absence of phantom pain, phantom and stump sensations or stump pain or both.

RESULTS

The response rate was 84%. Sixty-five (81%) participants returned the questionnaire. In 64 (98.5%) participants a traumatic injury led to amputation; the amputation was necessary because of infection in one patient (1.5%). The median follow-up time (from amputation to evaluation) was 3.2 years (range, 0.9-3.8 years) The prevalence of phantom pain was 44.6%, phantom sensation 53.8%, stump pain 61.5%, and stump sensation 78.5%. After its first appearance, phantom pain had a decreasing course in 14 (48.2%) of 29 amputees, was stable in 11 (37.9%) amputees, and worsened in 2 (6.9%) of 29 amputees. Stump pain had a decreasing course in 19 (47.5%) of 40 amputees but was stable in 12 (30%) amputees. Phantom pain occurred immediately after amputation in 8 (28%) of 29 amputees between 1 month and 12 months in 3 (10%) amputees and after 12 or more months in 12 (41%) amputees.

CONCLUSION

Stump pain and stump sensation predominate traumatic amputees' somatosensory experience immediately after amputation; phantom pain and phantom sensations are often long-term consequences of amputation. Amputees experience phantom sensations and phantom pain within 1 month after amputation, a second peak occurs 12 months after amputation. Revised diagnostic criteria for phantom pain are proposed on the basis of these data.

Age-dependent development of chronic neuropathic pain, allodynia and sensory recovery after upper limb nerve injury in children

Forty-nine children with distal upper limb nerve injury were studied at a mean follow-up of 2 years 3 months. Patients who were aged 5 years or younger at the time of nerve injury (15/49) had no chronic neuropathic pain symptoms or allodynia. Patients with allodynia on quantitative sensory testing but no spontaneous pain (8/49) were all older than 5 years and those reporting spontaneous chronic neuropathic pain (5/49) were all older than 12 years at the time of injury. Previous studies of adults with similar nerve injuries report chronic hyperaesthesia in up to 40% of cases. Semmes-Weinstein monofilament testing showed a positive correlation between age at injury and abnormal sensory threshold (r = 0.60, P<0.0001). These findings indicate that young children show better sensory recovery and are less likely to develop long-term chronic neuropathic pain syndromes than adults following nerve injury.