Proximal Muscles Of Upper Limbs Research Articles

Technical Aspects of Eliciting Trigeminocervical and Trigeminospinal Reflexes in Humans: A Scoping Review.

This scoping review aims to summarize the technical strategies for obtaining trigeminocervical reflex (TCR) and trigeminospinal reflex (TSR) responses. Studies published on TCR or TSR elicitation in humans through electrical stimulation of trigeminal nerve branches were eligible for this scoping review. The data of interest included stimulation parameters, site of stimulation, recording parameters, and the feasibility of TCR and TSR elicitation, in healthy participants. Short-latency TCR responses were regularly obtained in both anterior and posterior neck muscles after electrical stimulation of the supraorbital and infraorbital nerves under voluntary muscle activation. However, without voluntary muscle activation, we found evidence of elicitation of short-latency TCR components only in the posterior neck muscles after supraorbital or infraorbital nerve stimulation. Long-latency TCR responses were regularly obtained in the anterior and posterior neck muscles in studies that evaluated this technique, regardless of the trigeminal branch stimulation or muscle activation status. Short-latency TSR components were not obtained in the included studies, whereas long-latency TSR responses were regularly recorded in proximal upper limb muscles. This scoping review revealed key heterogeneity in the techniques used for TCR and TSR elicitation. By summarizing all the methodological procedures used for TCR and TSR elicitation, this scoping review can guide researchers in defining optimized technical approaches for different research and clinical scenarios.

Bilateral Parsonage-Turner syndrome after COVID-19 vaccination. A case report and review of the literature

Parsonage---Turner syndrome (PTS; neuralgic amyotrophy) is a generally unilateral neuritis with sudden onset, severe shoulder or upper arm pain. Although the intense pain is usually self-limiting, two-thirds of patients experience pro-gressive motor weakness, narrowed range of motion, reflex changes, dysesthesias and chronic neuropathic pain in the shoulder girdle musculature and proximal upper limb muscles. The aetiology is unclear, in addition to some idiopath-ic cases the most common triggers of PTS are surgery, trauma, infection or vaccination. It is reported after SARS-CoV-2 infection, and unilateral PTS has been described in some cases following different types of COVID-19 vaccines. We are currently presenting the case of a middle-aged woman who developed partial neuralgic amyotrophy on the right shoulder one month after receiving the second dose of the BNT162b2 COVID-19 mRNA vaccine (Pfizer-BioNTech), and seven months later the symptoms appeared in the contralateral upper limb. The diagnosis of PTS was also confirmed by magnetic resonance and electrodiagnostic examination. The PTS is not an uncommon condi-tion, but in the absence of knowledge it is rarely thought of. The purpose of this report is to draw attention to the possibility of PTS in shoulder or upper arm pain following both SARS-CoV-2 infection and COVID-19 vaccination, as early diagnosis and adequate therapy may help to shorten the course of the disease.

Modulation of Motor Evoked Potentials via the Cutaneous Silent Period within Proximal–Distal Muscles in the Upper-Limb

A single pulse of high intensity electrical current delivered to the digits of the hand during voluntary contractions produces a period of decreased electromyographic (EMG) activity, known as a cutaneous silent period (CSP) (Caccia and Violini, 1973; Inghilleri et al., 1997; Uncini et al., 1991). Pairing transcranial magnetic stimulation (TMS) with digit stimulation results in motor evoked potentials (MEPs) with reduced amplitudes in a thenar muscle (Kofler, 2008). It is not known if similar behavior can be observed in more proximal upper-limb muscles. The current study investigated the CSP on several muscles throughout the upper-limb. Fourteen subjects performed isometric contractions with the following muscles: abductor pollicis brevis (APB), flexor carpi radialis (FCR), extensor carpi radialis (ECR), biceps brachii (BIC), triceps brachii (TRI), anterior deltoid (AD), and posterior deltoid (PD). During the isometric contractions, subjects experienced three different stimulation conditions: electrical stimulation (10x perceptual threshold) of digit II only (CSP), transcranial magnetic stimulation only (TMS), and a pairing of digit II stimulation and TMS (TMS+). The TMS evoked MEP was significantly greater than the TMS+ MEP for APB (p < 0.001), FCR (p = 0.006), and BIC (p < 0.049) muscles. The opposite relationship was seen within the PD (p < 0.047) muscle. An ANOVA test of normalized MEP values (TMS+/TMS) showed significant differences in APB vs TRI (p = 0.004) and PD (p = 0.003), and in FCR vs TRI (p = 0.046) and PD (p = 0.037) muscles. The results suggest that the CSP modulates descending drive differentially across upper-limb muscles.

Good response to plasmapheresis and mycophenolate mofetil in a patient with anti-synthetase syndrome associated with peripheral neuritis and severe prosthetic aortic valve stenosis

BackgroundIdiopathic inflammatory myopathies (IIM) are a disease complex that encompasses several distinctly acquired muscle illnesses. Anti-synthetase syndrome is a subset of IIM that is characterized by the presence of antibodies against aminoacyl-tRNA synthetases (ARS). This syndrome has a characteristic phenotype of IIM. Anti-synthetase syndrome was rarely associated with peripheral nerve involvement and endocarditis.Case presentationWe report a 46-year-old female patient with a history of mitral and aortic valve replacement for seven years and on warfarin, presented with symmetrical muscular weakness, generalized edema, progressive dyspnea, dysphagia, fever, fatigue, myalgia, and polyarthralgia. The motor power grading was 2 in proximal muscles of upper limbs and 3 in the distal muscles involving hands and wrists, and it was 0 in proximal muscles in lower limbs and 2 in distal muscles involving ankle and toes movements. Also, her oxygen saturation decreased remarkably. Echocardiography revealed that the patient had severe stenosis (70%) of the prosthetic aortic valve. Electrophysiological studies showed axonal polyneuropathy with average F wave latencies. She was diagnosed with anti-synthetase syndrome for elevated muscle enzymes, interstitial lung disease (ILD), mechanic’s hands, fever, polyarthralgia, and positive anti-Jo-1 antibody. There was a significant improvement with plasmapheresis, mycophenolate mofetil (MMF), and high-dose prednisolone.ConclusionsTo the best of our knowledge, this is a case of anti-synthetase syndrome accompanied by neuropathic involvement and cardiac valve prosthetic stenosis. These were reported as an unusual presentation of the anti-synthetase syndrome. The significant improvement with plasmapheresis gives us a treatment choice for similar critical cases.

High prevalence of paraspinal muscle involvement in adults with McArdle disease.

Very few studies analyzing the pattern of muscle involvement in magnetic resonance imaging (MRI) of patients with McArdle disease have been reported to date. We aimed to examine the pattern of muscle fat replacement in patients with McArdle disease. We performed a retrospective study including all patients with genetically confirmed McArdle disease followed in our center from January 2010 to March 2021. Clinical data were collected from the medical record. Whole-body MRI was performed as part of the diagnostic evaluation. The distribution of muscle fat replacement and its severity were analyzed. Nine patients were included. Median age at onset was 7 y (range, 5-58) and median age at the time when MRI was performed was 57.3y (range, 37.2-72.8). At physical examination, four patients had permanent weakness: in three the weakness was limited to paraspinal muscles, whereas in one the weakness involved the paraspinal and proximal upper limb muscles. Muscle MRI showed abnormalities in six of the seven studied patients. In all of them, fat replacement of paravertebral muscles was found. Other muscles frequently affected were the tongue in three, subscapularis in three, and long head of biceps femoris and semimembranosus in two. Our findings suggest that paraspinal muscle involvement is common in McArdle disease and support the need to include this disease in the differential diagnosis of the causes of paraspinal muscle weakness. Involvement of the tongue and subscapularis are also frequent in McArdle disease.

Long-term Follow-up and Muscle Imaging Findings in Brachio-Cervical Inflammatory Myopathy.

ObjectiveTo report on a cohort of patients diagnosed with brachio-cervical inflammatory myopathy (BCIM), with specific focus on muscle MRI and follow-up data.MethodsClinical, histopathologic, serologic, and pre- and post-treatment MRI findings of patients diagnosed with BCIM were retrospectively evaluated.ResultsSix patients, all females with a mean age at onset of 53 years (range 37–62 years), were identified. Mean diagnostic delay was 17 months, and mean follow-up was 35 months. Most common clinical features encompassed predominant involvement of neck and proximal upper limb muscles, followed by distal upper limb, facial, and bulbar muscle weakness with different severity. Lower limb involvement was rare, although present in severe cases. Muscle biopsies showed a heterogeneous degree of perivascular and endomysial inflammatory changes. Myositis-specific antibodies were absent in all patients, whereas all resulted positive for antinuclear antibodies; half of the patients had anti–acetylcholine receptor antibodies without evidence of muscle fatigability. MRI showed disproportionate involvement of upper girdle and neck muscles compared with lower limbs, with frequent hyperintensities on short-tau inversion recovery sequences. Partial clinical and radiologic improvement with steroid and immunosuppressant therapy was obtained in most patients, especially in proximal upper limb muscles, whereas neck weakness persisted.ConclusionBCIM is an inflammatory myopathy with a peculiar clinical and radiologic presentation and a relatively broad spectrum of severity. Long-term follow-up data suggest that appropriate and early treatment can prevent chronic muscle function impairment. MRI characterization can be helpful in reducing diagnostic and treatment delay with positive consequence on clinical outcome.

Parsonage turner syndrome: a common syndrome usually missed

Background: Parsonage-turner syndrome (PTS) is a rare syndrome that can occur in normal healthy individuals with sudden, rather abrupt, unilateral shoulder pain that may begin rather insidiously but quickly amplifies in severity and intensity. The acute period of pain is subsequently replaced over a course of a few days to weeks with progressive weakness, reflex changes, and sensory abnormalities in varying presentations that typically involve the shoulder girdle musculature and proximal upper limb muscles. There are no definite etiological factors present in causation of this syndrome.Methods: Prospective multicentric cohort study covering period from 2010 to 2020. 10 young male patients were included in the study group, all of them presented with winging of scapula and pain. Initial evaluation was done at neurology department and after failure of conservative treatment of average period of six month they were referred to plastic surgery department. All patients had ENMG findings preoperatively.Results: 10 male patients were studied with average age of 24.8 years. Partial paralysis present for an average of 1 year. Repeated micro trauma was the most common aetiology. Intraoperatively 7 patients had anomalous vascular compression of long thoracic nerve (LTN) and three had compression due to fibrous sheath. All patients had complete recovery at end of one year.Conclusion: Isolated LTN paralysis is a rare condition that is not well known. If conservative management fails, then neurolysis of the distal segment of LTN gives good result if performed within 6-12 months of paralysis.

Proximal Upper Limb Sensorimotor Integration in Response to Novel Motor Skill Acquisition.

Previous studies have shown significant changes in cortical and subcortical evoked potential activity levels in response to motor training with the distal upper-limb muscles. However, no studies to date have assessed the neurological processing changes in somatosensory evoked potentials (SEPs) associated with motor training whole-arm movements utilizing proximal upper-limb muscles. The proximal upper-limb muscles are a common source of work-related injuries, due to repetitive glenohumeral movements. Measuring neurophysiological changes following performance of a proximal motor task provide insight into potential neurophysiological changes associated with occupational postures and movements involving proximal upper limb muscles. This study sought to assess the impact of a novel motor skill acquisition task on neural processing of the proximal upper-limb muscle groups, through the measurement of short-latency median nerve SEPs. One group of 12 participants completed a novel motor training task, consisting of tracing a sinusoidal waveform varying in amplitude and frequency. Baseline SEP measurements were recorded from each participant, followed by a mental recitation control task. Pre-test SEP measurements were then recorded, followed by the motor training task, and post-test SEP recordings. The participants completed the tracing with their right thumb, using glenohumeral rotation only to move their hand. Significant improvements in task accuracy were demonstrated, indicating that motor acquisition had occurred. Significant changes were also seen in the N11, N13, N20, N24, P25, and the N30 SEP peaks were seen following the motor training task. Conclusion: Early SEPs appear to be a sensitive measure of changes in sensorimotor integration in response to novel motor skill acquisition within the proximal upper-limb muscles.

A novel PNPLA2 mutation causing total loss of RNA and protein expression in two NLSDM siblings with early onset but slowly progressive severe myopathy

Neutral lipid storage disease with myopathy (NLSDM) is a rare autosomal recessive disorder, due to an enzymatic error of lipid metabolism. Patients present always with skeletal muscle myopathy and variable cardiac and hepatic involvement. NLSDM is caused by mutations in the PNPLA2 gene, which encodes the adipose triglyceride lipase (ATGL). Here we report the molecular characterization and clinical findings of two NLSDM siblings carrying the novel c.187+1G > C homozygous PNPLA2 mutation, localized in the splice site of intron 2. Molecular analyses revealed that neither aberrant PNPLA2 mRNA isoforms, nor ATGL mutated protein were detectable in patient's cells.Clinically, both patients presented early onset muscle weakness, in particular of proximal upper limb muscles. In almost 15 years, muscle damage affected also distal upper limbs.This is a NLSDM family, displaying a severe PNPLA2 mutation in two siblings with clinical presentation characterized by an early onset, but a slowly evolution of severe myopathy.

PROXIMAL BRACHIAL MONOMELIC AMYOTROPHY OR HIRAYAMA DISEASE: NO LONGER AN ALIAS? (case report)

Background. Brachial Monomelic Amyotrophy (BMMA) has been called as Hirayama disease (HD) when it is characterized by unilateral distal upper limb weakness and atrophy that shows progression for a limited period and is associated with typical features on MRI of cervical spine in flexion.&#x0D; Objective was to explore the differences when BMMA affects the proximal upper limb muscles with the help of case report.&#x0D; Methods. A case report of BMMA in an adult Indian male is represented.&#x0D; Results. A 30-year-old man presented to us with a history of weakness in the proximal aspect of his left upper limb that began four years ago. The weakness was progressive up until 6 months prior to his presentation since when the weakness had neither worsened nor improved. Cervical spine contrast enhanced MRI revealed mild loss of cervical lordosis, but no features of HD like localized cord atrophy, loss of attachment of dura from subjacent lamina on neutral position axial T2WI MRI, nor any presence of posterior epidural crescentic enhancing mass on flexion contrast sagittal T1WI MRI. The patient was managed with supportive therapy and has been under regular follow up ever since. His clinical status has been stable.&#x0D; Conclusions. We support the suggestion to consider proximal Brachial Monomelic Amyotrophy to be a separate entity and to be distinguished from Hirayama disease that should be reserved for patients with distal upper limb involvement with cervical MRI findings on flexion studies.

Botulinum toxin A injection in the management of shoulder muscle overactivity: A scoping review

AbstractThe majority of studies examining botulinum toxin A (BTX-A) in the management of upper limb muscle overactivity and pain focus on the distal arm and hand. Research has begun to look at BTX-A efficacy in more proximal upper limb muscles, with literature showing equivocal findings. This scoping review identified 15 studies meeting inclusion criteria whose data were examined against three outcome variables: muscle overactivity, range of movement and pain. Overall, while the majority of injected participants improved on these variables, between-study methodological variability such as research design potentially underpowered studies and arbitrary decision making gave a high likelihood of influencing the interpretation of their results. Future research is warranted, with a robust focus on functional anatomy, a critical appraisal of how BTX-A may help the individual being studied and utilising individualised rather than protocol-driven research paradigms.

An Acute Pharyngeal-Cervical-Brachial (PCB) variant of Guillain-Barre Syndrome

Acute Guillain Barre Syndrome [GBS] is characterized by an acute onset of limb weakness and areflexia. There are a few rare variants that have been described and one of them is the pharyngeal–cervical-brachial[PCB] variant [involving oropharynx, neck and proximal upper limb muscles]. Many neurologists and physicians are unaware of this variant which is often misdiagnosed as myasthenia gravis, brainstem stroke or botulism. A 37 year old female patient presented with the classical characteristics including bulbar weakness, cervicobrachial weakness and are flexia in the upper limbs, with relatively preserved lower limbs. Her systemic review was unremarkable. Her physical examination was compatible with GBS. Nerve conduction studies revealed Motor Axonal Radiculoneuropathy. She received 5 day course of IVIG and showed significant improvement over next 1 week. The patient recovered well and was discharged after 12 days. Keywords: Guillain Barre Syndrome, Pharyngeal-Cervical-Brachial Variant

Lesiones musculoesqueléticas no específicas de la musculatura proximal del miembro superior en el personal sanitario: un análisis de la presencia de puntos gatillo

High labor demands in hospitals are associated to muscle pain, hyperalgesia, functional restrictions and behavioral disorders accompanied by muscle injuries. However, most of the research has focused on evaluating ergonomics, stress and workload. ObjectivesTo determine how many workers in a hospital showed non-specific musculoskeletal disorders (MSDs) confirmed by the presence of Trigger Points (TrPs); to establish the most affected muscles (i. e., sternocleidomastoid, levator scapula, trapeze, infraspinatus, teres minor) by pain according to the side (left or right); and to identify the pain behavior assumed. Material and methodA cross-sectional study was conducted at the Loire VendéeOcéan Hospital, France. The pressure pain threshold measured by algometry was bilaterally compared and evaluated in the proximal upper limb muscles (PULM). Pain behavior was assessed using a self-administered questionnaire. Results21 women suffered from non-specific MSDs in PULM, confirmed by TrPs. The pressure pain threshold at the sternocleidomastoid was significant and bilaterally lower compared to other muscles (F4,200=48.879; P<.01). Self-medication for pain relief was frequent in 61.90% of patients. ConclusionsImplementation of active break-time programs aimed to specific muscular groups is required to reduce the risk musculoskeletal disorders in the PULM in the hospital setting. Future studies could investigate if the increased pain in the sternocleidomastoid may be explained by short episodes of low-amplitude but long-duration contractions.

Are ipsilateral motor evoked potentials subject to intracortical inhibition?

Paired-pulse transcranial magnetic stimulation (TMS) can be used to examine intracortical inhibition in primary motor cortex (M1), termed short-interval intracortical inhibition (SICI). To our knowledge, SICI has only been demonstrated in contralateral motor evoked potentials (MEPs). Ipsilateral MEPs (iMEPs) are assumed to reflect excitability of an uncrossed oligosynaptic pathway, and can sometimes be evoked in proximal upper-limb muscles using high-intensity TMS. We examined whether iMEPs in the biceps brachii (BB) would be suppressed by subthreshold conditioning, therefore demonstrating SICI of iMEPs. TMS was delivered to the dominant M1 to evoke conditioned (C) and nonconditioned (NC) iMEPs in the nondominant BB of healthy participants during weak bilateral elbow flexion. The conditioning stimulus intensities tested were 85%, 100%, and 115% of active motor threshold (AMT), at 2 ms and 4 ms interstimulus intervals (ISI). The iMEP ratio (C/NC) was calculated for each condition to assess the amount of inhibition. Inhibition of iMEPs was present at 2 ms ISI with 100% and 115% AMT (bothP< 0.03), mediated by a reduction in persistence and size (allP< 0.05). To our knowledge, this is the first demonstration of SICI of iMEPs. This technique may be useful as a tool to better understand the role of ipsilateral M1 during functional motor tasks.

Enhanced motor learning with bilateral transcranial direct current stimulation: Impact of polarity or current flow direction?

Bilateral transcranial direct current stimulation (TDCS) is superior to unilateral TDCS when targeting motor learning. This effect could be related to either the current flow direction or additive polarity-specific effects on each hemisphere. This sham-controlled randomized study included fifty right-handed healthy subjects in a parallel-group design who performed an exoskeleton-based motor task of the proximal left arm on three consecutive days. Prior to training, we applied either sham, right anodal (a-TDCS), left cathodal (c-TDCS), concurrent a-TDCS and c-TDCS with two independent current sources and return electrodes (double source (ds)-TDCS) or classical bilateral stimulation (bi-TDCS). Motor performance improved over time for both unilateral (a-TDCS, c-TDCS) and bilateral (bi-TDCS, ds-TDCS) TDCS montages. However, only the two bilateral paradigms led to an improvement of the final motor performance at the end of the training period as compared to the sham condition. There was no difference between the two bilateral stimulation conditions (bi-TDCS, ds-TDCS). Bilateral TDCS is more effective than unilateral stimulation due to its polarity-specific effects on each hemisphere rather than due to its current flow direction. This study is the first systematic evaluation of stimulation polarity and current flow direction of bi-hemispheric motor cortex TDCS on motor learning of proximal upper limb muscles.

Reorganization of spinal neural circuitry and functional recovery after spinal cord injury

Reorganization of spinal neural circuitry and functional recovery after spinal cord injury

Muscle strength in myasthenia gravis

Myasthenia gravis (MG) is characterized by fatigue and fluctuating muscle weakness as a result of impaired neuromuscular transmission (NMT). Although MG is a prototypic fatiguing disorder, little is known about how the condition affects fixed weakness, and if present, whether weakness is related to disease duration or gender. The aim of this study was to quantify the strength of patients with MG and investigate whether it is related to disease duration. Eight muscle groups were tested by manual muscle testing and with a hand-held dynamometer in 38 patients with generalized MG and 37 healthy age- and gender-matched controls. The disease duration was recorded and compared with strength measures. On average, muscle strength was decreased by 28% compared with controls (P<0.01). Repeated strength measures in individual patients did not differ, suggesting that the muscle force reported was not subject to fatigue, but reflected fixed weakness. The male patients showed a greater reduction in muscle force in all eight muscle groups than women with MG (60% vs 77% of normal, P<0.05). In both men and women with MG, strength in shoulder abductors was most affected (51% vs 62% of normal). Muscle strength and disease duration were not related. These findings show that patients with generalized MG have (i) a significant generalized, fixed muscle weakness, (ii) that male patients with MG have a more severe muscle weakness than women, (iii) that proximal upper limb muscles are most affected, and (iv) that disease duration alone is not a predictor of loss of muscle strength.

IS 21. tDCS effects on ipsilateral motor control: Robbing Peter to pay Paul?

In humans both cerebral hemispheres play an essential role in controlling the upper limb. However, the neurophysiological effects of noninvasive brain stimulation (NBS) of primary motor cortex (M1) have been investigated primarily from motor evoked potentials (MEPs) recorded in contralateral distal hand muscles alone. This may present an incomplete picture. For example, the idea of using NBS after stroke to suppress excitability of the contralesional hemisphere (cM1), or “re-balance” excitability, may be too simplistic, and may lead to undesirable outcomes for some patients. The purpose of this presentation is to show how NBS alters excitability of projections to contralateral and ipsilateral motoneurons (MNs) controlling the proximal upper limb, and in particular, the cortico-reticulo-propriospinal pathway (CRPP). This has implications for the use of NBS as adjuvants to upper limb rehabilitation after stroke. Experiments involved TMS to elicit MEPs in distal and proximal upper limb muscles, M1 cathodal t-DCS (c-tDCS), and sham control. Effects of M1 c-tDCS and sham were compared in healthy participants and patients with upper limb weakness after sub-cortical stroke. M1 c-tDCS modulated ipsilateral and contralateral MEPs in proximal upper limb muscles in a task-dependent manner, at least in part via the CRPP. In stroke patients, cM1 c-tDCS modified selectivity of paretic biceps brachii (BB). Mildly impaired patients showed improved selectivity, whereas moderate-severely impaired patients showed worsened selectivity, and modulation of ipsilateral BB MEPs after cM1 c-tDCS correlated with clinical, neurophysiological and neuroimaging measures. In patients with upper limb weakness after stroke, the role of the cM1 for upper limb control can vary between individuals, depending on extent of damage to the corticospinal pathway. We present a neurophysiological model that explains how the cM1 may gain control of the paretic arm via the CRPP and why suppression of cM1 with NBS can be beneficial for some patients, but detrimental for others. Finally we describe ways to predict whether cM1 suppression may be indicated or contraindicated for an individual patient after stroke.

Recruitment of ipsilateral and contralateral upper limb muscles following stimulation of the cortical motor areas in the monkey

It is well established that cortical motor stimulation results in contralateral upper limb (UL) activity. Motor responses are also elicited in the ipsilateral UL, though controversy surrounds the significance of these effects. Evidence suggests that ipsilateral muscle activity is more common following the stimulation of the supplementary motor area (SMA) and dorsal premotor area (PMd), compared to the primary motor cortex (M1), but none of these studies compared effects from all three areas in the same subjects. This has limited our understanding of how these three cortical motor areas influence ipsilateral UL muscle activity. The purpose of this study was to determine the contribution of each of three cortical areas to the production of ipsilateral and contralateral UL. To maximize sensitivity and allow comparison of the effects across cortical areas, we applied the same stimulation parameters (36 pulse stimulus train at 330 Hz) to M1, SMA, and PMd in three adult M. fascicularis and recorded electromyographic (EMG) activity from muscles in the trunk and both ULs. Of all muscle responses identified, 24 % were ipsilateral to the stimulation, mostly in proximal muscles. The highest percentage of ipsilateral responses occurred following SMA stimulation. We also observed that PMd stimulation elicited more suppression responses compared with stimulation of M1 and SMA. The results indicate that ipsilateral motor areas provide a significant contribution to cortical activation of the trunk and proximal UL muscles. These understudied pathways may represent a functional substrate for future strategies to shape UL recovery following injury or stroke.

Cortical mapping of the infraspinatus muscle in healthy individuals

BackgroundWhile cortical representations of intrinsic hand muscles have been extensively studied in healthy individuals, little is known about the representation of proximal upper limb muscles. Improving our understanding of normal shoulder function is important, given that shoulder musculoskeletal disorders affect approximately 20% of the population and are suspected to involve changes in central motor representations. The purpose of the study is to describe the motor representation (motor evoked potentials (MEP) amplitude at the hotspot, map area, normalized map volume and center of gravity) of the infraspinatus muscle in healthy individuals, and to explore the potential influence of hand dominance on this representation (i.e. symmetry of the excitability and of the location of motor map between sides), as well as the effect of age and gender on motor excitability.ResultsFifteen healthy participants took part in this study. No significant asymmetry between sides was observed for motor excitability (p = 0.14), map area (p = 0.73) and normalized map volume (p = 0.34). Moreover, no side x intensity interaction was found (p = 0.54), indicating similar stimulus response properties. No difference between sides was found in the location of infraspinatus motor representation, either in the mediolateral or anteroposterior axis (p > 0.10). Neither age nor gender influenced aMT (p > 0.58) or MEP size (p > 0.61).ConclusionsAs the cortical representation of infraspinatus muscles was found to be symmetric between sides, both in terms of excitability and location, comparisons between the intact and affected side could be performed in clinical studies, regardless of whether the dominant or non-dominant side is affected. The next step will be to characterize corticospinal excitability and map parameters in populations with shoulder disorders.