Increased excitability in the primary motor cortex and supplementary motor area in patients with phantom limb pain after upper limb amputation

Cortical Reorganization after Limb Loss: Bridging the Gap between Basic Science and Clinical Recovery

Despite the increasing incidence and prevalence of amputation across the globe, individuals with acquired limb loss continue to struggle with functional recovery and chronic pain. A more complete understanding of the motor and sensory remodeling of the peripheral and central nervous system that occurs postamputation may help advance clinical interventions to improve the quality of life for individuals with acquired limb loss. The purpose of this article is to first provide background clinical context on individuals with acquired limb loss and then to provide a comprehensive review of the known motor and sensory neural adaptations from both animal models and human clinical trials. Finally, the article bridges the gap between basic science researchers and clinicians that treat individuals with limb loss by explaining how current clinical treatments may restore function and modulate phantom limb pain using the underlying neural adaptations described above. This review should encourage the further development of novel treatments with known neurological targets to improve the recovery of individuals postamputation.Significance Statement In the United States, 1.6 million people live with limb loss; this number is expected to more than double by 2050. Improved surgical procedures enhance recovery, and new prosthetics and neural interfaces can replace missing limbs with those that communicate bidirectionally with the brain. These advances have been fairly successful, but still most patients experience persistent problems like phantom limb pain, and others discontinue prostheses instead of learning to use them daily. These problematic patient outcomes may be due in part to the lack of consensus among basic and clinical researchers regarding the plasticity mechanisms that occur in the brain after amputation injuries. Here we review results from clinical and animal model studies to bridge this clinical-basic science gap.

The modulation effects of the mind-body and physical exercises on the basolateral amygdala-temporal pole pathway on individuals with knee osteoarthritis

Background/Objective

To investigate the modulatory effects of different physical exercise modalities on connectivity of amygdala subregions and its association with pain symptoms in patients with knee osteoarthritis (KOA).

Methods

140 patients with KOA were randomly allocated either to the Tai Chi, Baduanjin, Stationary cycling, or health education group and conducted a 12 week-long intervention in one of the four groups. The behavioral, magnetic resonance imaging (MRI), and blood data were collected at baseline and the end of the study.

Results

Compared to the control group, all physical exercise modalities lead to significant increases in Knee Injury and Osteoarthritis Outcome Score (KOOS) pain score (pain relief) and serum Programmed Death-1 (PD-1) levels. Additionally, all physical exercise modalities resulted in decreased resting state functional connectivity (rsFC) of the basolateral amygdala (BA)-temporal pole and BA-medial prefrontal cortex (mPFC). The overlapping BA-temporal pole rsFC observed in both Tai Chi and Baduanjin groups was significantly associated with pain relief, while the BA-mPFC rsFC was significantly associated with PD-1 levels. In addition, we found increased fractional anisotropy (FA) values, a measurement of water diffusion anisotropy of tissue that responded to changes in brain microstructure, within the mind-body exercise groups' BA-temporal pole pathway. The average FA value of this pathway was positively correlated with KOOS pain score at baseline across all subjects.

Conclusions

Our findings suggest that physical exercise has the potential to modulate both functional and anatomical connectivity of the amygdala subregions, indicating a possible shared pathway for various physical exercise modalities.

Stimulation of peroneal nerves reveals maintained somatosensory representation in transtibial amputees

Introduction

Several studies have found changes in the organization of the primary somatosensory cortex (SI) after amputation. This SI reorganization was mainly investigated by stimulating neighboring areas to amputation. Unexpectedly, the somatosensory representation of the deafferented limb has rarely been directly tested.

Methods

We stimulated the truncated peroneal nerve in 24 unilateral transtibial amputees and 15 healthy controls. The stimulation intensity was adjusted to make the elicited percept comparable between both stimulation sides. Neural sources of the somatosensory-evoked magnetic fields (SEFs) to peroneal stimulation were localized in the contralateral foot/leg areas of SI in 19 patients and 14 healthy controls.

Results

We demonstrated the activation of functionally preserved cortical representations of amputated lower limbs. None of the patients reported evoked phantom limb pain (PLP) during stimulation. Stimulation that evoked perceptions in the foot required stronger intensities on the amputated side than on the intact side. In addition to this, stronger stimulation intensities were required for amputees than for healthy controls. Exploratorily, PLP intensity was neither associated with stimulation intensity nor dipole strength nor with differences in Euclidean distances (between SEF sources of the healthy peroneus and mirrored SEF sources of the truncated peroneus).

Discussion

Our results provide hope that the truncated nerve may be used to establish both motor control and somatosensory feedback via the nerve trunk when a permanently functional connection between the nerve trunk and the prosthesis becomes available.

Peripheral Nerve Injury Induces Changes in the Activity of Inhibitory Interneurons as Visualized in Transgenic GAD1-GCaMP6s Rats

Peripheral nerve injury induces cortical remapping that can lead to sensory complications. There is evidence that inhibitory interneurons play a role in this process, but the exact mechanism remains unclear. Glutamate decarboxylase-1 (GAD1) is a protein expressed exclusively in inhibitory interneurons. Transgenic rats encoding GAD1–GCaMP were generated to visualize the activity in GAD1 neurons through genetically encoded calcium indicators (GCaMP6s) in the somatosensory cortex. Forepaw denervation was performed in adult rats, and fluorescent Ca2+ imaging on cortical slices was obtained. Local, intrahemispheric stimulation (cortical layers 2/3 and 5) induced a significantly higher fluorescence change of GAD1-expressing neurons, and a significantly higher number of neurons were responsive to stimulation in the denervated rats compared to control rats. However, remote, interhemispheric stimulation of the corpus callosum induced a significantly lower fluorescence change of GAD1-expressing neurons, and significantly fewer neurons were deemed responsive to stimulation within layer 5 in denervated rats compared to control rats. These results suggest that injury impacts interhemispheric communication, leading to an overall decrease in the activity of inhibitory interneurons in layer 5. Overall, our results provide direct evidence that inhibitory interneuron activity in the deprived S1 is altered after injury, a phenomenon likely to affect sensory processing.

Pain's Adverse Impact on Training-Induced Performance and Neuroplasticity: A Systematic Review

Motor training is a widely used therapy in many pain conditions. The brain’s capacity to undergo functional and structural changes i.e., neuroplasticity is fundamental to training-induced motor improvement and can be assessed by transcranial magnetic stimulation (TMS). The aim was to investigate the impact of pain on training-induced motor performance and neuroplasticity assessed by TMS. The review was carried out in accordance with the PRISMA-guidelines and a Prospero protocol (CRD42020168487). An electronic search in PubMed, Web of Science and Cochrane until December 13, 2019, identified studies focused on training-induced neuroplasticity in the presence of experimentally-induced pain, 'acute pain' or in a chronic pain condition, 'chronic pain'. Included studies were assessed by two authors for methodological quality using the TMS Quality checklist, and for risk of bias using the Newcastle–Ottawa Scale. The literature search identified 231 studies. After removal of 71 duplicates, 160 abstracts were screened, and 24 articles were reviewed in full text. Of these, 17 studies on acute pain (n = 7) or chronic pain (n = 10), including a total of 258 patients with different pain conditions and 248 healthy participants met the inclusion criteria. The most common types of motor training were different finger tasks (n = 6). Motor training was associated with motor cortex functional neuroplasticity and six of seven acute pain studies and five of ten chronic pain studies showed that, compared to controls, pain can impede such trainings-induced neuroplasticity. These findings may have implications for motor learning and performance and with putative impact on rehabilitative procedures such as physiotherapy.

Decoding attempted phantom hand movements from ipsilateral sensorimotor areas after amputation

Objective.The sensorimotor cortex is often selected as target in the development of a Brain-Computer Interface, as activation patterns from this region can be robustly decoded to discriminate between different movements the user executes. Up until recently, such BCIs were primarily based on activity in the contralateral hemisphere, where decoding movements still works even years after denervation. However, there is increasing evidence for a role of the sensorimotor cortex in controlling the ipsilateral body. The aim of this study is to investigate the effects of denervation on the movement representation on the ipsilateral sensorimotor cortex.Approach.Eight subjects with acquired above-elbow arm amputation and nine controls performed a task in which they made (or attempted to make with their phantom hand) six different gestures from the American Manual Alphabet. Brain activity was measured using 7T functional MRI, and a classifier was trained to discriminate between activation patterns on four different regions of interest (ROIs) on the ipsilateral sensorimotor cortex.Main results.Classification scores showed that decoding was possible and significantly better than chance level for both the phantom and intact hands from all ROIs. Decoding both the left (intact) and right (phantom) hand from the same hemisphere was also possible with above-chance level classification score.Significance.The possibility to decode both hands from the same hemisphere, even years after denervation, indicates that implantation of motor-electrodes for BCI control possibly need only cover a single hemisphere, making surgery less invasive, and increasing options for people with lateralized damage to motor cortex like after stroke.

Agonist-antagonist myoneural interface amputation preserves proprioceptive sensorimotor neurophysiology in lower limbs

The brain undergoes marked changes in function and functional connectivity after limb amputation. The agonist-antagonist myoneural interface (AMI) amputation is a procedure that restores physiological agonist-antagonist muscle relationships responsible for proprioceptive sensory feedback to enable greater motor control. We compared results from the functional neuroimaging of individuals (n = 29) with AMI amputation, traditional amputation, and no amputation. Individuals with traditional amputation demonstrated a significant decrease in proprioceptive activity, measured by activation of Brodmann area 3a, whereas functional activation in individuals with AMIs was not significantly different from controls with no amputation (P < 0.05). The degree of proprioceptive activity in the brain strongly correlated with fascicle activity in the peripheral muscles and performance on motor tasks (P < 0.05), supporting the mechanistic basis of the AMI procedure. These results suggest that surgical techniques designed to restore proprioceptive peripheral neuromuscular constructs result in desirable central sensorimotor plasticity.

Typical somatomotor physiology of the hand is preserved in a patient with an amputated arm: An ECoG case study

Electrophysiological signals in the human motor system may change in different ways after deafferentation, with some studies emphasizing reorganization while others propose retained physiology. Understanding whether motor electrophysiology is retained over longer periods of time can be invaluable for patients with paralysis (e.g. ALS or brainstem stroke) when signals from sensorimotor areas may be used for communication or control over neural prosthetic devices. In addition, a maintained electrophysiology can potentially benefit the treatment of phantom limb pains through prolonged use of these signals in a brain-machine interface (BCI). Here, we were presented with the unique opportunity to investigate the physiology of the sensorimotor cortex in a patient with an amputated arm using electrocorticographic (ECoG) measurements. While implanted with an ECoG grid for clinical evaluation of electrical stimulation for phantom limb pain, the patient performed attempted finger movements with the contralateral (lost) hand and executed finger movements with the ipsilateral (healthy) hand. The electrophysiology of the sensorimotor cortex contralateral to the amputated hand remained very similar to that of hand movement in healthy people, with a spatially focused increase of high-frequency band (65-175 Hz; HFB) power over the hand region and a distributed decrease in low-frequency band (15-28 Hz; LFB) power. The representation of the three different fingers (thumb, index and little) remained intact and HFB patterns could be decoded using support vector learning at single-trial classification accuracies of >90%, based on the first 1-3 s of the HFB response. These results indicate that hand representations are largely retained in the motor cortex. The intact physiological response of the amputated hand, the high distinguishability of the fingers and fast temporal peak are encouraging for neural prosthetic devices that target the sensorimotor cortex.

Surgical prevention of terminal neuroma and phantom limb pain: a literature review

The incidence of extremity amputation is estimated at about 200,000 cases annually. Over 25% of patients suffer from terminal neuroma or phantom limb pain (TNPLP), resulting in pain, inability to wear a prosthetic device, and lost work. Once TNPLP develops, there is no definitive cure. Therefore, there has been an emerging focus on TNPLP prevention. We examined the current literature on TNPLP prevention in patients undergoing extremity amputation. A literature review was performed using Ovid Medline, Cochrane Collaboration Library, and Google Scholar to identify all original studies that addressed surgical prophylaxis against TNPLP. The search was conducted using both Medical Subject Headings and free-text using the terms “phantom limb pain,” “amputation neuroma,” and “surgical prevention of amputation neuroma.” Fifteen studies met the inclusion criteria, including six prospective trials, two comprehensive literature reviews, four retrospective chart reviews, and three case series/technique reviews. Five techniques were identified, and each was incorporated into a target-based classification system. A small but growing body of literature exists regarding the surgical prevention of TNPLP. Targeted muscle reinnervation (TMR), a form of physiologic target reassignment, has the greatest momentum in the academic surgical community, with multiple recent prospective studies demonstrating superior prevention of TNPLP. Neurorrhaphy and transposition with implantation are supported by less robust evidence, but merit future study as alternatives to TMR.

Changes in Temporal and Spatial Patterns of Intrinsic Brain Activity and Functional Connectivity in Upper-Limb Amputees: An fMRI Study

Background

Amputation in adults is a serious procedure or traumatic outcome, one that leads to a possible “remapping” of limb representations (somatotopy) in the motor and sensory cortex. The temporal and spatial extent underlying reorganization of somatotopy is unclear. The aim of this study was to better understand how local and global structural plasticity in sensory-motor cortical networks changes temporally and spatially after upper-limb amputation.

Methods

We studied 8 healthy nonamputee control subjects and 16 complete upper-limb amputees. Resting-state MRI (rs-fMRI) was used to measure local and large-scale relative differences (compared to controls) in both the amplitude of low-frequency fluctuations (ALFF) and degree of centrality (DC) at 2 months, 6 months, and 12 months after traumatic amputation.

Results

In amputees, rs-fMRI scans revealed differences in spatial patterns of ALFF and DC among brain regions over time. Significant relative increases in ALFF and DC were detected not only in the sensory and motor cortex but also in related cortical regions believed to be involved in cognition and motor planning. We observed changes in the magnitude of ALFFs in the pre- and postcentral gyrus and primary sensory cortex, as well as in the anterior cingulate, parahippocampal gyrus, and hippocampus, 2 months after the amputation. The regional distribution of increases/decreases in ALFFs and DC documented at 2-month postamputation was very different from those at 6 and 12-month postamputation.

Conclusion

Local and wide-spread changes in ALFFs in the sensorimotor cortex and cognitive-related brain regions after upper-limb amputation may imply dysfunction not only in sensory and motor function but also in areas responsible for sensorimotor integration and motor planning. These results suggest that cortical reorganization after upper extremity deafferentation is temporally and spatially more complicated than previously appreciated, affecting DC in widespread regions.

Non-invasive neuromodulation using rTMS and the electromagnetic-perceptive gene (EPG) facilitates plasticity after nerve injury

BACKGROUND

Twenty million Americans suffer from peripheral nerve injury. These patients often develop chronic pain and sensory dysfunctions. In the past decade, neuroimaging studies showed that these changes are associated with altered cortical excitation-inhibition balance and maladaptive plasticity. We tested if neuromodulation of the deprived sensory cortex could restore the cortical balance, and whether it would be effective in alleviating sensory complications.

OBJECTIVE

We tested if non-invasive repetitive transcranial magnetic stimulation (rTMS) which induces neuronal excitability, and cell-specific magnetic activation via the Electromagnetic-perceptive gene (EPG) which is a novel gene that was identified and cloned from glass catfish and demonstrated to evoke neural responses when magnetically stimulated, can restore cortical excitability.

METHODS

A rat model of forepaw denervation was used. rTMS was delivered every other day for 30 days, starting at the acute or at the chronic post-injury phase. A minimally-invasive neuromodulation via EPG was performed every day for 30 days starting at the chronic phase. A battery of behavioral tests was performed in the days and weeks following limb denervation in EPG-treated rats, and behavioral tests, fMRI and immunochemistry were performed in rTMS-treated rats.

RESULTS

The results demonstrate that neuromodulation significantly improved long-term mobility, decreased anxiety and enhanced neuroplasticity. The results identify that both acute and delayed rTMS intervention facilitated rehabilitation. Moreover, the results implicate EPG as an effective cell-specific neuromodulation approach.

CONCLUSION

Together, these results reinforce the growing amount of evidence from human and animal studies that are establishing neuromodulation as an effective strategy to promote plasticity and rehabilitation.

Electroacupuncture-Induced Plasticity between Different Representations in Human Motor Cortex

Somatosensory stimulation can effectively induce plasticity in the motor cortex representation of the stimulated body part. Specific interactions have been reported between different representations within the primary motor cortex. However, studies evaluating somatosensory stimulation-induced plasticity between different representations within the primary motor cortex are sparse. The purpose of this study was to investigate the effect of somatosensory stimulation on the modulation of plasticity between different representations within the primary motor cortex. Twelve healthy volunteers received both electroacupuncture (EA) and sham EA at the TE5 acupoint (located on the forearm). Plasticity changes in different representations, including the map volume, map area, and centre of gravity (COG) were evaluated by transcranial magnetic stimulation (TMS) before and after the intervention. EA significantly increased the map volume of the forearm and hand representations compared to those of sham EA and significantly reduced the map volume of the face representation compared to that before EA. No significant change was found in the map volume of the upper arm and leg representations after EA, and likewise, no significant changes in map area and COG were observed. These results suggest that EA functions as a form of somatosensory stimulation to effectively induce plasticity between different representations within the primary motor cortex, which may be related to the extensive horizontal intrinsic connectivity between different representations. The cortical plasticity induced by somatosensory stimulation might be purposefully used to modulate human cortical function.

Protective and Risk Factors for Phantom Limb Pain and Residual Limb Pain Severity

INTRODUCTION

The exact mechanisms underlying the development and maintenance of phantom limb pain (PLP) are still unclear. This study aimed to identify the factors affecting pain intensity in patients with chronic, lower limb, traumatic PLP.

METHODS

This is a cross-sectional analysis of patients with PLP. We assessed amputation-related and pain-related clinical and demographic variables. We used univariate and multivariate models to evaluate the associated factors modulating PLP and residual limb pain (RLP) intensity.

RESULTS

We included 71 unilateral traumatic lower limb amputees. Results showed that (1) amputation-related perceptions were experienced by a large majority of the patients with chronic PLP (sensations: 90.1%, n = 64; residual pain: 81.7%, n = 58); (2) PLP intensity has 2 significant protective factors (phantom limb movement and having effective treatment for PLP previously) and 2 significant risk factors (phantom limb sensation intensity and age); and (3) on the other hand, for RLP, risk factors are different: presence of pain before amputation and level of amputation (in addition to the same protective factors).

CONCLUSION

These results suggest different neurobiological mechanisms to explain PLP and RLP intensity. While PLP risk factors seem to be related to maladaptive plasticity, since phantom sensation and older age are associated with more pain, RLP risk factors seem to have components leading to neuropathic pain, such as the amount of neural lesion and previous history of chronic pain. Interestingly, the phantom movement appears to be protective for both phenomena.

Repetitive Magnetic Stimulation for the Management of Peripheral Neuropathic Pain: A Systematic Review

INTRODUCTION

Repetitive magnetic stimulation (rMS) is a safe and well-tolerated intervention. Transcranial magnetic stimulation (TMS) is used for the treatment of depression and for the treatment and prevention of migraine. Over the last few years, several reports and randomised controlled studies of the use of rMS for the treatment of pain have been published. The aim of this systematic review was to identify the available literature regarding the use of rMS in the treatment of peripheral neuropathic pain.

METHODS

After a systematic Medline search we identified 12 papers eligible to be included in this review.

RESULTS

The majority of the studies were on patients with phantom limb pain, followed by radiculopathy, plexopathy, post-traumatic pain and peripheral neuropathy. The treatment protocols vary significantly from study to study and, therefore, pooling the results together is currently difficult. However, rMS has a definite immediate effect in pain relief which, in the majority of studies, is maintained for a few weeks.

CONCLUSION

rMS seems to be a promising intervention in the treatment of peripheral neuropathic pain. Further research is in the field is needed. Use of neuronavigation might increase the precision of stimulation and subsequently its effectiveness.

Neural modifications in lower limb amputation: an fMRI study on action and non-action oriented body representations

The loss of sensorimotor and visual information that follows limb amputation is known to affect both the action-oriented (body schema, BS) and non-action oriented (NA) body representations. However, the neural underpinnings of these effects have not yet been fully understood. We investigated the neural correlates of body representations in a group of 9 healthy right-handed individuals with left lower limb amputation (LLA) and 11 healthy age-matched controls (HC) by using event-related functional magnetic resonance imaging. Participants were scanned while performing mental rotation of body parts (i.e. hand, foot and eye) and objects (i.e. a rear-view mirror). Although the performance of LLA were similar to that of HC, they showed a different activation profile in relation to both BS and to NA within a wide range of brain areas. The bilateral intraparietal sulcus was less activated in LLA than HC, whereas the bilateral anterior insula as well as the fusiform body area, the precentral gyrus, the supplementary motor area in the left hemisphere and the inferior occipital gyrus in the right hemisphere were more activated during the mental rotation of left stimuli in the LLA. Also, the left EBA showed higher activation during the mental rotation of the foot than that of the eye in the LLA but not in the HC. Our results are consistent with the hypothesis that left LLA yields to a modification in the body representation network even when it does not lead to clear behavioral deficits.

Neuroplasticity Modifications Following a Lower-Limb Amputation: A Systematic Review

BACKGROUND

Although there are studies that have examined brain functional reorganization following upper-limb amputation, understanding of the brain changes that occur in people with lower-limb amputation is limited.

OBJECTIVE

To investigate modifications in the brain following lower-limb amputation.

METHODS

We included case-control studies that evaluate neuroplasticity in the central nervous system using neuroimaging techniques. A literature search was conducted using MEDLINE, CINAHL, Web of Science, Scopus, and Cochrane.

RESULTS

Eleven articles were included (total n = 204 people with unilateral lower-limb amputation). These studies showed an increase in cerebellar gray matter volume in prosthesis users, as well as a decrease in thickness of the premotor cortex, orbitofrontal cortex, temporo-occipital junction, precentral gyrus, visual areas, and somatosensory cortex. Regarding white matter, the trials observed a decrease in the integrity at the corona radiata, the connections between the premotor areas, the fronto-occipital fasciculus and the corpus callosum. In addition, a decreased functional connectivity between cortical and subcortical areas has been described.

CONCLUSIONS

Lower-limb amputation causes changes in several brain structures that may occur in the absence of pain and regardless of prosthesis use. The modifications observed include thinning or loss of gray matter volume, decrease in the integrity of the white matter connections between brain structures and changes in the functional connectivity between cortical and subcortical areas.

LEVEL OF EVIDENCE

I.

Characterizing the Structural Pattern Predicting Medication Response in Herpes Zoster Patients Using Multivoxel Pattern Analysis

Herpes zoster (HZ) can cause a blistering skin rash with severe neuropathic pain. Pharmacotherapy is the most common treatment for HZ patients. However, most patients are usually the elderly or those that are immunocompromised, and thus often suffer from side effects or easily get intractable post-herpetic neuralgia (PHN) if medication fails. It is challenging for clinicians to tailor treatment to patients, due to the lack of prognosis information on the neurological pathogenesis that underlies HZ. In the current study, we aimed at characterizing the brain structural pattern of HZ before treatment with medication that could help predict medication responses. High-resolution structural magnetic resonance imaging (MRI) scans of 14 right-handed HZ patients (aged 61.0 ± 7.0, 8 males) with poor response and 15 (aged 62.6 ± 8.3, 5 males) age- (p = 0.58), gender-matched (p = 0.20) patients responding well, were acquired and analyzed. Multivoxel pattern analysis (MVPA) with a searchlight algorithm and support vector machine (SVM), was applied to identify the spatial pattern of the gray matter (GM) volume, with high predicting accuracy. The predictive regions, with an accuracy higher than 79%, were located within the cerebellum, posterior insular cortex (pIC), middle and orbital frontal lobes (mFC and OFC), anterior and middle cingulum (ACC and MCC), precuneus (PCu) and cuneus. Among these regions, mFC, pIC and MCC displayed significant increases of GM volumes in patients with poor response, compared to those with a good response. The combination of sMRI and MVPA might be a useful tool to explore the neuroanatomical imaging biomarkers of HZ-related pain associated with medication responses.

The Interactive Effect of Tonic Pain and Motor Learning on Corticospinal Excitability

Prior work showed differential alterations in early somatosensory evoked potentials (SEPs) and improved motor learning while in acute tonic pain. The aim of the current study was to determine the interactive effect of acute tonic pain and early motor learning on corticospinal excitability as measured by transcranial magnetic stimulation (TMS). Two groups of twelve participants (n = 24) were randomly assigned to a control (inert lotion) or capsaicin (capsaicin cream) group. TMS input–output (IO) curves were performed at baseline, post-application, and following motor learning acquisition. Following the application of the creams, participants in both groups completed a motor tracing task (pre-test and an acquisition test) followed by a retention test (completed without capsaicin) within 24–48 h. Following an acquisition phase, there was a significant increase in the slope of the TMS IO curves for the control group (p < 0.05), and no significant change for the capsaicin group (p = 0.57). Both groups improved in accuracy following an acquisition phase (p < 0.001). The capsaicin group outperformed the control group at pre-test (p < 0.005), following an acquisition phase (p < 0.005), and following a retention test (p < 0.005). When data was normalized to the pre-test values, the learning effects were similar for both groups post-acquisition and at retention (p < 0.005), with no interactive effect of group. The acute tonic pain in this study was shown to negate the increase in IO slope observed for the control group despite the fact that motor performance improved similarly to the control group following acquisition and retention. This study highlights the need to better understand the implications of neural changes accompanying early motor learning, particularly while in pain.

Action and Non-Action Oriented Body Representations: Insight from Behavioural and Grey Matter Modifications in Individuals with Lower Limb Amputation

Objective

Following current model of body representations, we aimed to systematically investigate the association between brain modifications, in terms of grey matter loss, and body representation deficits, in terms of alterations of the body schema (BS) and of non-action oriented body representations (NA), in individuals with lower limb amputation (LLA).

Method

BS and NA (both semantic and visuospatial NA) were evaluated in 11 healthy controls and in 14 LLA, considering the impact of clinical variables such as prosthesis use. The association between BS and NA deficits and grey matter loss was also explored in LLA by using Voxel Based Morphometry analysis.

Results

LLA's performance was fine in terms of semantic NA, while it showed behavioural impairments both in BS and visuospatial NA as compared to healthy controls. Interestingly the visuospatial NA performance was related to the amount of prosthesis use. NA deficits in terms of visuospatial body map processing were associated with grey matter reduction in left (lobule VIII) and right (crus II) cerebellum, while BS deficits were associated with grey matter reduction in right anterior cingulate cortex and the bilateral cuneus. No significant association was detected for semantic NA.

Conclusion

The study of BS and NA representations after limb loss has informed our understanding of the different dynamics (i.e., adjustments to body change) of such representations, supporting current cognitive models of body representation. The clinical relevance of present findings is also discussed.

Cerebellar grey matter modifications in lower limb amputees not using prosthesis

Plastic brain changes following peripheral deafferentation, in particular those following limb amputations, are well-documented, with significant reduction of grey matter (GM) in the sensory-motor cerebral areas representing the amputated limb. However, few studies have investigated the role played by the use of a prosthesis in these structural brain modifications. Here we hypothesized that using a functional prosthesis that allows individuals to perform actions may reduce grey matter reduction. We investigated the brain structural reorganization following lower limb amputation by using a Voxel Based Morphometry (VBM) analysis of structural magnetic resonance imaging (MRI) in 8 right-handed individuals with lower limb amputation (LLA) fitted with prostheses (LLAwp), compared to 6 LLA who had never used a prosthesis (LLAnp). 14 age-matched healthy controls were also enrolled (HC). We did not find any significant effect when comparing LLAwp and HC. However we found a decreased GM volume in the bilateral cerebellum in LLAnp compared with HC. These results suggest that prosthesis use prevents GM decrease in the cerebellum after lower limb amputation.

Preservation of hand movement representation in the sensorimotor areas of amputees

Denervation due to amputation is known to induce cortical reorganization in the sensorimotor cortex. Although there is evidence that reorganization does not lead to a complete loss of the representation of the phantom limb, it is unclear to what extent detailed, finger-specific activation patterns are preserved in motor cortex, an issue that is also relevant for development of brain-computer interface solutions for paralysed people. We applied machine learning to obtain a quantitative measure for the functional organization within the motor and adjacent cortices in amputees, using high resolution functional MRI and attempted hand gestures. Subjects with above-elbow arm amputation (n = 8) and non-amputated controls (n = 9) made several gestures with either their right or left hand. Amputees attempted to make gestures with their amputated hand. Images were acquired using 7 T functional MRI. The sensorimotor cortex was divided into four regions, and activity patterns were classified in individual subjects using a support vector machine. Classification scores were significantly above chance for all subjects and all hands, and were highly similar between amputees and controls in most regions. Decodability of phantom movements from primary motor cortex reached the levels of right hand movements in controls. Attempted movements were successfully decoded from primary sensory cortex in amputees, albeit lower than in controls but well above chance level despite absence of somatosensory feedback. There was no significant correlation between decodability and years since amputation, or age. The ability to decode attempted gestures demonstrates that the detailed hand representation is preserved in motor cortex and adjacent regions after denervation. This encourages targeting sensorimotor activity patterns for development of brain-computer interfaces.

Altered thalamic connectivity during spontaneous attacks of migraine without aura: A resting-state fMRI study

Background

Functional connectivity of brain networks may be altered in migraine without aura patients. Functional magnetic resonance imaging (fMRI) studies have demonstrated changed activity in the thalamus, pons and cerebellum in migraineurs. Here, we investigated the thalamic, pontine and cerebellar network connectivity during spontaneous migraine attacks.

Methods

Seventeen patients with episodic migraine without aura underwent resting-state fMRI scan during and outside of a spontaneous migraine attack. Primary endpoint was a difference in functional connectivity between the attack and the headache-free days. Functional connectivity was assessed in four different networks using seed-based analysis. The chosen seeds were in the thalamus (MNI coordinates x,y,z: right, 22,–24,0 and left, –22,–28,6), pons (right, 8,–24,–32 and left, –8,–24,–32), cerebellum crus I (right, 46,–58,–30 and left, –46,–58,–30) and cerebellum lobule VI (right, 34,–42,–36 and left, –32,–42,–36).

Results

We found increased functional connectivity between the right thalamus and several contralateral brain regions (superior parietal lobule, insular cortex, primary motor cortex, supplementary motor area and orbitofrontal cortex). There was decreased functional connectivity between the right thalamus and three ipsilateral brain areas (primary somatosensory cortex and premotor cortex). We found no change in functional connectivity in the pontine or the cerebellar networks.

Conclusions

The study indicates that network connectivity between thalamus and pain modulating as well as pain encoding cortical areas are affected during spontaneous migraine attacks.

Relationship between chronic pain and brain reorganization after deafferentation: A systematic review of functional MRI findings

Background

Mechanisms underlying the development of phantom limb pain and neuropathic pain after limb amputation and spinal cord injury, respectively, are poorly understood. The goal of this systematic review was to assess the robustness of evidence in support of “maladaptive plasticity” emerging from applications of advanced functional magnetic resonance imaging (MRI).

Methods

Using MeSH heading search terms in PubMed and SCOPUS, a systematic review was performed querying published manuscripts.

Results

From 146 candidate publications, 10 were identified as meeting the inclusion criteria. Results from fMRI investigations provided some level of support for maladaptive cortical plasticity, including longitudinal studies that demonstrated a change in functional organization related to decreases in pain. However, a number of studies have reported no relationship between reorganization, pain and deafferentation, and emerging evidence has also suggested the opposite — that is, chronic pain is associated with preserved cortical function.

Conclusion

Based solely on advanced functional neuroimaging results, there is only limited evidence for a relationship between chronic pain intensity and reorganization after deafferentation. The review demonstrates the need for additional neuroimaging studies to clarify the relationship between chronic pain and reorganization.

•

There is evidence of a relationship between brain reorganization, deafferentation, and chronic pain.

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Emerging evidence suggests that reorganization in the CNS could be an adaptive process, preventing the emergence of pain.

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Future studies adopting standardized protocols are needed to clarify the role of chronic pain and plasticity in the brain.

Successful Treatment of Phantom Limb Pain by 1 Hz Repetitive Transcranial Magnetic Stimulation Over Affected Supplementary Motor Complex: A Case Report

A 37-year-old man with a right transfemoral amputation suffered from severe phantom limb pain (PLP). After targeting the affected supplementary motor complex (SMC) or primary motor cortex (PMC) using a neuro-navigation system with 800 stimuli of 1 Hz repetitive transcranial magnetic stimulation (rTMS) at 85% of resting motor threshold, the 1 Hz rTMS over SMC dramatically reduced his visual analog scale (VAS) of PLP from 7 to 0. However, the 1 Hz rTMS over PMC failed to reduce pain. To our knowledge, this is the first case report of a successfully treated severe PLP with a low frequency rTMS over SMC in affected hemisphere.

Primary Motor Cortex Representation of Handgrip Muscles in Patients with Leprosy

BACKGROUND

Leprosy is an endemic infectious disease caused by Mycobacterium leprae that predominantly attacks the skin and peripheral nerves, leading to progressive impairment of motor, sensory and autonomic function. Little is known about how this peripheral neuropathy affects corticospinal excitability of handgrip muscles. Our purpose was to explore the motor cortex organization after progressive peripheral nerve injury and upper-limb dysfunction induced by leprosy using noninvasive transcranial magnetic stimulation (TMS).

METHODS

In a cross-sectional study design, we mapped bilaterally in the primary motor cortex (M1) the representations of the hand flexor digitorum superficialis (FDS), as well as of the intrinsic hand muscles abductor pollicis brevis (APB), first dorsal interosseous (FDI) and abductor digiti minimi (ADM). All participants underwent clinical assessment, handgrip dynamometry and motor and sensory nerve conduction exams 30 days before mapping. Wilcoxon signed rank and Mann-Whitney tests were performed with an alpha-value of p<0.05.

FINDINGS

Dynamometry performance of the patients' most affected hand (MAH), was worse than that of the less affected hand (LAH) and of healthy controls participants (p = 0.031), confirming handgrip impairment. Motor threshold (MT) of the FDS muscle was higher in both hemispheres in patients as compared to controls, and lower in the hemisphere contralateral to the MAH when compared to that of the LAH. Moreover, motor evoked potential (MEP) amplitudes collected in the FDS of the MAH were higher in comparison to those of controls. Strikingly, MEPs in the intrinsic hand muscle FDI had lower amplitudes in the hemisphere contralateral to MAH as compared to those of the LAH and the control group. Taken together, these results are suggestive of a more robust representation of an extrinsic hand flexor and impaired intrinsic hand muscle function in the hemisphere contralateral to the MAH due to leprosy.

CONCLUSION

Decreased sensory-motor function induced by leprosy affects handgrip muscle representation in M1.

Immediate and Sustained Effects of 5-Day Transcranial Direct Current Stimulation of the Motor Cortex in Phantom Limb Pain

The study explored the analgesic effects of transcranial direct current stimulation (tDCS) over the motor cortex on postamputation phantom limb pain (PLP). Eight subjects with unilateral lower or upper limb amputation and chronic PLP were enrolled in a crossover, double-blind, sham-controlled treatment program. For 5 consecutive days, anodal (active or sham) tDCS was applied over the motor cortex for 15 minutes at an intensity of 1.5 mA. The 5-day treatment with active, but not sham, tDCS induced a sustained decrease in background PLP and in the frequency of PLP paroxysms, which lasted for 1 week after the end of treatment. Moreover, on each day of active tDCS, patients reported an immediate PLP relief, along with an increased ability to move their phantom limb. Patients' immediate responses to sham tDCS, on the contrary, were variable, marked by an increase or decrease of PLP levels from baseline. These results show that a 5-day treatment of motor cortex stimulation with tDCS can induce stable relief from PLP in amputees. Neuromodulation targeting the motor cortex appears to be a promising option for the management of this debilitating neuropathic pain condition, which is often refractory to classic pharmacologic and surgical treatments.

PERSPECTIVE

The study describes sustained and immediate effects of motor cortex stimulation by tDCS on postamputation PLP, whose analgesic action seems linked to the motor reactivation of the phantom limb. These results are helpful for the exploitation of tDCS as a therapeutic tool for the management of neuropathic pain.

Intra-operative transdural electric stimulation in awake patient: target refining for motor cortex stimulation

INTRODUCTION

Most authors perform the implantation of epidural electrodes for motor cortex stimulation (MCS) under general anesthesia, using navigation merely based on anatomic landmarks or in combination with intra-operative sensory evoked potentials (SEP) for functional localization. However, intra-operative SEP can only provide the localization of central sulcus in patients who present sensory pathways which are at least partially preserved. Conversely, there are massive deafferentation pain syndromes (e.g., brachial plexus avulsion or amputation) in which the peripheral sensory pathways are severely or totally injured, precluding the use of intra-operative SEP. Objective. The authors present a simple technique for functional localization and intra-operative mapping of motor cortex by the implementation of transdural electrical stimulation of cerebral cortex for target refining of motor cortex during cortical electrode implantation procedures.

METHODS

Thirteen patients with complete brachial plexus root avulsion suffering from severe neuropathic pain in the affected limb were included in this report. First, the anatomical location of the motor cortex of the hand was stereotactically determined by the hand knob within the central sulcus. Functional mapping of cortex was performed by transdural bipolar electrical stimulation under local anesthesia, so patients were fully awake during the whole time of cortical mapping. The cortical mapping oriented the placement of epidural electrodes for chronic cortical stimulation for treatment of neuropathic pain.

RESULTS

Stereotactic MR images of the hand knob were considered a satisfactory landmark for the motor area of the hand in all patients. On top of the anatomical landmark, transdural electrical stimulation (4.0-6.0 mA, 30-60 Hz and pulse width of 1 ms) gave vivid sensations of movement in the deafferented hand, forearm, and arm. The phantom sensation was elicited with lower current than usual motor mapping in patients with intact limbs. It was possible to delineate the spatial map of the phantom hand on the cortical surface with acceptable resolution. The sensation of wrist flexion was elicited in all; most of the patients had clear distinction of the thumb and index. The remaining fingers were not perceived individually. The cortical area responsive to the thumb tended to occupy a lateral position related to the areas of the other fingers, following the maps of the normal homunculus. The evoked sensation was restricted to the period of stimulation, and it stopped as soon as that was discontinued. The stimulation also evoked emotional responses related to sensation of limb movement.

CONCLUSION

The proposed technique was useful for target refining in implantation of epidural electrode for motor cortex stimulation. Further studies are required to investigate if target refining by intra-operative mapping will significantly improve the results in the treatment of refractory pain.

Specific neck training induces sustained corticomotor hyperexcitability as assessed by motor evoked potentials

STUDY DESIGN

Experimental investigation of short-term and long-term corticomotor effects of specific neck training, coordination training, and no training.

OBJECTIVE

To determine the effects of different training programs on the motor neurons controlling the neck muscles as well as the effects of training on muscle strength and muscle fatigue, and the correlations between corticomotor control and motor learning.

SUMMARY OF BACKGROUND DATA

Training is usually recommended for unspecific neck pain and consists of neck and upper body coordination, strengthening, and endurance exercises. However, it is unclear which type of training is the most effective. No studies have previously investigated the neural effect of neck training and the possible differential effect of specific versus coordination training on corticomotor control.

METHODS

Transcranial magnetic stimulation and electromyography were used to elicit and monitor motor evoked potentials (MEPs) from the trapezius and thumb muscles before and 30 minutes, 1 hour, and 7 days after training. Parameters measured were MEP amplitude, MEP latency, strength, learning effects, and muscle fatigue.

RESULTS

Only specific neck training yielded a 67% increase in MEP amplitudes for up to 7 days after training compared with baseline (P < 0.001). No significant changes were seen after coordination training, no training, and in the within-subject control muscle. The mean muscle strength increased immediately after specific neck training from 56.6 to 61 kg (P < 0.001). No subjective or objective measures of fatigue were observed.

CONCLUSION

Specific neck training induced a sustained hyperexcitability of motor neurons controlling the neck muscles compared with coordination training and controls. These findings may prove valuable in the process of developing more effective clinical training programs for unspecific neck pain.

Multivariate classification of structural MRI data detects chronic low back pain

Chronic low back pain (cLBP) has a tremendous personal and socioeconomic impact, yet the underlying pathology remains a mystery in the majority of cases. An objective measure of this condition, that augments self-report of pain, could have profound implications for diagnostic characterization and therapeutic development. Contemporary research indicates that cLBP is associated with abnormal brain structure and function. Multivariate analyses have shown potential to detect a number of neurological diseases based on structural neuroimaging. Therefore, we aimed to empirically evaluate such an approach in the detection of cLBP, with a goal to also explore the relevant neuroanatomy. We extracted brain gray matter (GM) density from magnetic resonance imaging scans of 47 patients with cLBP and 47 healthy controls. cLBP was classified with an accuracy of 76% by support vector machine analysis. Primary drivers of the classification included areas of the somatosensory, motor, and prefrontal cortices--all areas implicated in the pain experience. Differences in areas of the temporal lobe, including bordering the amygdala, medial orbital gyrus, cerebellum, and visual cortex, were also useful for the classification. Our findings suggest that cLBP is characterized by a pattern of GM changes that can have discriminative power and reflect relevant pathological brain morphology.

Brain connectivity abnormalities extend beyond the sensorimotor network in peripheral neuropathy

OBJECTIVES

To investigate, using resting state (RS) functional connectivity (FC), the selectivity of involvement of the sensorimotor network in patients with acquired (A) and with hereditary (H) peripheral neuropathies (PN) and the correlations of RS FC abnormalities with clinical impairment and structural brain damage. Temporal associations among RS networks were also explored.

EXPERIMENTAL DESIGN

RS fMRI scans were acquired from 13 APN, 12 HPN, and 18 age- and sex-matched healthy controls. Independent component analysis and functional network connectivity were used to investigate RS FC within and among RS networks with potential functional relevance.

PRINCIPAL OBSERVATIONS

Compared to controls, patients had a decreased FC of the right precentral gyrus and an increased RS FC of the precuneus within the sensorimotor network. Both decreased and increased RS FC also involved the visual and auditory networks, which additionally had an increased coherence of function with the sensorimotor network (more pronounced in HPN). RS FC modifications in patients extended to several cognitive networks and were correlated with disease duration. In APN, they were also correlated with the severity of clinical impairment and corpus callosum atrophy.

CONCLUSIONS

In PN, RS FC modifications extend beyond the sensorimotor network and involve other sensory and cognitive networks. The correlations between RS FC patterns and disease duration in patients as well as with clinical impairment in patients with APN suggest that modifications of FC might reflect an adaptive mechanism, which takes time to occur and helps to limit the clinical consequences of peripheral damage.

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.

Former hand territory activity increases after amputation during intact hand movements, but is unaffected by illusory visual feedback

BACKGROUND

In healthy adults, hand movements are controlled largely by the contralateral primary motor cortex. Following amputation, however, movements of the intact hand are accompanied by increased activity in the sensorimotor cortices of both cerebral hemispheres.

OBJECTIVE

The authors tested whether use of the intact hand reactivates the cortical territory formerly devoted to the now missing hand and whether these effects can be augmented by motor imagery (MI) and/or exposure to illusory visual "feedback" (VF) of the absent hand created with a mirror.

METHODS

Functional magnetic resonance imaging (fMRI) was used to delineate the boundaries of normative sensorimotor hand representations in healthy controls. Brain activity from 11 unilateral hand amputees was recorded while they performed aurally paced thumb-finger sequencing movements with their intact hands under 4 conditions: (1) motor execution of the intact hand alone (ME), (2) ME with corresponding MI of the amputated hand, (3) ME with VF of the amputated hand, and (4) ME with MI and VF.

RESULTS

Intact hand movements increased activity specifically within the former sensorimotor hand territory during all conditions, an effect that may be attributable to decreased levels of interhemispheric inhibition and/or use-dependent functional reorganization following amputation. This effect was not significantly increased by the addition of VF and/or MI of the amputated hand. However, in amputees, MI was associated with an expansion of this ipsilateral response into parietal, premotor, and presupplementary motor areas.

CONCLUSION

Active engagement of the intact hand may be critical for therapies seeking to stimulate the former hand territory.

Neural correlates of an illusory touch experience investigated with fMRI

When asked to judge the presence or absence of near-threshold tactile stimuli, participants often report touch experiences when no tactile stimulation has been delivered ('false alarms'). The simultaneous presentation of a light flash during the stimulation period can increase the frequency of touch reports, both when touch is and is not present. Using fMRI, we investigated the BOLD response during both light-present and light-absent false alarms, testing predictions concerning two possible neural mechanisms underlying these illusory touch experiences: activation of a tactile representation in primary somatosensory cortex (SI) and/or activation of a tactile representation in late processing areas outside of sensory-specific cortex, such as medial prefrontal cortex (MPC). Our behavioural results showed that participants made false alarms in light-present and light-absent trials, both of which activated regions of the medial parietal and medial prefrontal cortex including precuneus, posterior cingulate and paracingulate cortex, suggesting the same underlying mechanism. However, only a non-significant increase in SI activity was measured in response to false alarm vs. correct rejection trials. We argue that our results provide evidence for the role of top-down regions in somatic misperception, consistent with findings from studies in humans and non-human primates.

Optogenetic-guided cortical plasticity after nerve injury

Peripheral nerve injury causes sensory dysfunctions that are thought to be attributable to changes in neuronal activity occurring in somatosensory cortices both contralateral and ipsilateral to the injury. Recent studies suggest that distorted functional response observed in deprived primary somatosensory cortex (S1) may be the result of an increase in inhibitory interneuron activity and is mediated by the transcallosal pathway. The goal of this study was to develop a strategy to manipulate and control the transcallosal activity to facilitate appropriate plasticity by guiding the cortical reorganization in a rat model of sensory deprivation. Since transcallosal fibers originate mainly from excitatory pyramidal neurons somata situated in laminae III and V, the excitatory neurons in rat S1 were engineered to express halorhodopsin, a light-sensitive chloride pump that triggers neuronal hyperpolarization. Results from electrophysiology, optical imaging, and functional MRI measurements are concordant with that within the deprived S1, activity in response to intact forepaw electrical stimulation was significantly increased by concurrent illumination of halorhodopsin over the healthy S1. Optogenetic manipulations effectively decreased the adverse inhibition of deprived cortex and revealed the major contribution of the transcallosal projections, showing interhemispheric neuroplasticity and thus, setting a foundation to develop improved rehabilitation strategies to restore cortical functions.

Structural Brain Imaging: A Window into Chronic Pain

Structural imaging is turning our attention regarding the effects of chronic pain on the brain as a possible source of chronicity. Several independent studies have suggested a decrease in gray matter in pain-transmitting areas in patients with constant pain. Most of these data are discussed as representing damage or loss of brain gray matter, reinforcing the idea of chronic pain as a progressive disease. However, any data of an increase or decrease in gray matter in pain syndromes need to be considered in light of all observations gathered in the past 10 years and probably do not justify a discussion of brain damage or consideration of whether the disease is progressive. It is likely that these changes are the consequence and not the cause of the respective pain syndromes as they may reverse once the pain is adequately treated. Moreover, structural changes of the brain may not be specific to a particular pain syndrome and for the moment only mirror the magnitude or duration of pain suffered. The topographical distributions of gray matter changes may well be the consequence of cortical regions having varying susceptibilities. We need to better understand the behavioral consequences and cellular mechanisms underlying these neuroanatomic changes.

Effects of acupuncture on the brain hemodynamics

Acupuncture therapy has been applied to various psychiatric diseases and chronic pain since acupuncture stimulation might affect brain activity. From this point of view, we investigated the effects of acupuncture on autonomic nervous system and brain hemodynamics in human subjects using ECGs, EEGs and near-infrared spectroscopy (NIRS). Our previous studies reported that changes in parasympathetic nervous activity were correlated with number of de-qi sensations during acupuncture manipulation. Furthermore, these autonomic changes were correlated with EEG spectral changes. These results are consistent with the suggestion that autonomic changes induced by needle manipulation inducing specific de-qi sensations might be mediated through the central nervous system, especially through the forebrain as shown in EEG changes, and are beneficial to relieve chronic pain by inhibiting sympathetic nervous activity. The NIRS results indicated that acupuncture stimulation with de-qi sensation significantly decreased activity in the supplementary motor complex (SMC) and dorsomedial prefrontal cortex (DMPFC). Based on these results, we review that hyperactivity in the SMC is associated with dystonia and chronic pain, and that in the DMPFC is associated with various psychiatric diseases with socio-emotional disturbances such as schizophrenia, attention deficit hyperactive disorder, etc. These findings along with the previous studies suggest that acupuncture with de-qi sensation might be effective to treat the various diseases in which hyperactivity in the SMA and DMPFC is suspected of playing a role.

Cerebral hemodynamic responses induced by specific acupuncture sensations during needling at trigger points: a near-infrared spectroscopic study

Acupuncture stimulation at specific points, or trigger points (TPs), elicits sensations called "de-qi". De-qi sensations relate to the clinical efficacy of the treatment. However, it is neither clear whether de-qi sensations are associated with TPs, nor clear whether acupuncture effects on brain activity are associated with TPs or de-qi. We recorded cerebral hemodynamic responses during acupuncture stimulation at TPs and non-TPs by functional near-infrared spectroscopy. The acupuncture needle was inserted into both TPs and non-TPs within the right extensor muscle in the forearm. Typical acupuncture needle manipulation was conducted eight times for 15 s. The subjects pressed a button if they felt a de-qi sensation. We investigated how hemodynamic responses related to de-qi sensations induced at TPs and non-TPs. We observed that acupuncture stimulations producing de-qi sensations significantly decreased the Oxy-Hb concentration in the supplementary motor area (SMA), pre-supplementary motor area, and anterior dorsomedial prefrontal cortex regardless of the point stimulated. The hemodynamic responses were statistically analyzed using a general linear model and a boxcar function approximating the hemodynamic response. We observed that hemodynamic responses best fit the boxcar function when an onset delay was introduced into the analyses, and that the latency of de-qi sensations correlated with the onset delay of the best-fit function applied to the SMA. Our findings suggest that de-qi sensations favorably predict acupuncture effects on cerebral hemodynamics regardless of the type of site stimulated. Also, the effect of acupuncture stimulation in producing de-qi sensation was partly mediated by the central nervous system including the SMA.

Motor cortex dysfunction in complex regional pain syndrome

OBJECTIVE

Most patients with complex regional pain syndrome (CRPS) exhibit debilitating motor symptoms. The effect of continuous pain on motor system in CRPS, however, is not well known. We searched for signs of motor cortex dysfunction in chronic CRPS type 1 patients with motor impairment.

METHODS

We recorded rhythmic brain activity with magnetoencephalography (MEG) during noxious thulium-laser stimulation of both hands in eight CRPS patients and eight control subjects. We measured excitability of the motor cortex by monitoring the reactivity of the approximately 20-Hz motor cortex rhythm to laser stimuli. The reactivity was defined as a sum of the stimulus-induced suppression and the subsequent rebound of the approximately 20-Hz rhythm.

RESULTS

In CRPS, the reactivity of the approximately 20-Hz rhythm in the hemisphere contralateral to the painful hand was significantly weaker than in control subjects. The reactivity correlated with the mean level of the spontaneous pain (r=-0.64, P=0.04). Suppression of the approximately 20-Hz rhythm correlated with the grip strength in the painful hand (r=0.66, P=0.04).

CONCLUSION

Continuous pain in CRPS is associated with attenuated motor cortex reactivity.

SIGNIFICANCE

Abnormal motor cortex reactivity may be linked with motor dysfunction of the affected hand in CRPS.

Phantom limb phenomena in cancer amputees

PURPOSE

The objective of this study was to determine the prevalence of phantom pain and correlated conditions such as phantom sensations and stump pain in a population of cancer patients who had undergone limb amputation.

METHOD

A cross-sectional study was carried out in adult patients submitted to limb amputation, who were being followed up at the Physiotherapy Department between April 3 and November 30, 2006. The presence of phantom pain and associated conditions was quantified using a verbal numerical scale. The data obtained were analyzed for means, medians, and proportions with their respective confidence intervals, as appropriate.

RESULTS

Seventy-five patients participated in this study, 50 men (66.7%) and 25 women (33.3%). Mean age was 54.4 years (SD +/- 18.5); range 19 to 88 years. The prevalence of phantom pain was 46.7% (95%CI: 35.1 to 58.6), phantom sensation 90.7% (95%CI: 81.7 to 96.2), and surgical stump pain 32.0% (95%CI: 21.7 to 43.8).

CONCLUSION

Phantom pain and phantom sensations are highly prevalent among cancer patients. Further studies should be carried out to determine the main factors associated with their onset.

Ipsilateral cortical fMRI responses after peripheral nerve damage in rats reflect increased interneuron activity

In the weeks following unilateral peripheral nerve injury, the deprived primary somatosensory cortex (SI) responds to stimulation of the ipsilateral intact limb as demonstrated by functional magnetic resonance imaging (fMRI) responses. The neuronal basis of these responses was studied by using high-resolution fMRI, in vivo electrophysiological recordings, and juxtacellular neuronal labeling in rats that underwent an excision of the forepaw radial, median, and ulnar nerves. These nerves were exposed but not severed in control rats. Significant bilateral increases of fMRI responses in SI were observed in denervated rats. In the healthy SI of the denervated rats, increases in fMRI responses were concordant with increases in local field potential (LFP) amplitude and an increased incidence of single units responding compared with control rats. In contrast, in the deprived SI, increases in fMRI responses were associated with a minimal change in LFP amplitude but with increased incidence of single units responding. Based on action potential duration, juxtacellular labeling, and immunostaining results, neurons responding to intact forepaw stimulation in the deprived cortex were identified as interneurons. These results suggest that the increases in fMRI responses in the deprived cortex reflect increased interneuron activity.

The roles of predisposing characteristics, established need, and enabling resources on upper extremity prosthesis use and abandonment

PURPOSE

Prosthesis use and abandonment is a complex function of variables defining the contextualized individual. This review presents a comprehensive panoramic of these factors as related to the management of upper limb deficiency. Me

METHOD

nderson's model for health service utilization was used to frame prosthesis use and abandonment as a function of (1) predisposing characteristics of the individual (e.g. gender or level of limb loss); (2) established need, as characterized by lifestyle- and age-related demands; and (3) enabling resources (e.g. clinical and social). English-language articles pertaining to these components were identified in a search of Ovid, PubMed, ISI Web of Science and www.scholar.google.com (1980-November 2006) for key words upper limb and prosthesis. Approximately 90 articles were included as evidence in this review. Re

RESULTS

ersonal and contextual factors are critical determinants of prosthesis acceptance. While the influence of some factors (i.e. lifestyle, level of limb loss), is strongly supported in the literature, the impact of others, (i.e. age of fitting, efficacy of training protocols), remain controversial. Co

CONCLUSIONS

nhanced understanding of these factors is required to optimize clinical practices, guide design efforts, and satiate demand for evidence-based measures of intervention. Future research should comprise of controlled, multifactor studies adopting standardized outcome measures and providing comprehensive descriptions of population characteristics.