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Highlights • Contralateral reflex responses are present during cooperative hand movements in spinal cord injury (SCI) patients. • Ipsilateral SSEP during cooperative and also non-cooperative hand movements are enhanced in SCI patients. • Cooperative hand movements involve ipsi- and contralateral tract fibers. Abstract Objectives To evaluate whether the task-specific neural coupling mechanism during the performance of cooperative hand movements is preserved in tetraplegic subjects. Methods Recordings of ipsilateral and contralateral electromyographic reflex responses in activated forearm muscles and bilateral somatosensory potentials (SSEP) to unilateral ulnar nerve stimulations during rest, cooperative and non-cooperative hand movements. Results Contralateral reflex responses were present in almost all patients during cooperative hand movements but small in amplitude when hand function was severely impaired. Ipsilateral SSEP potentials were enhanced during both cooperative and, in contrast to healthy subjects, also non-cooperative bimanual movements. Conclusions Both results indicate a strong involvement of ipsilateral non-damaged cervical tracts and hemispheres in the control of bimanual hand movements in tetraplegic subjects. Significance This study on the neural control of bimanual movements in patients suffering a cervical injury allows designing therapeutic approaches for the improvement of hand function that are based on physiological insights. [ABSTRACT FROM AUTHOR]

Objective Contractions of the target muscle influence the aftereffects of repetitive transcranial magnetic stimulation (rTMS). The aim of this paper is to investigate whether or not voluntary hand movement influences the aftereffects of quadripulse stimulation (QPS) on the hand motor area. Methods Thirteen healthy volunteers participated in this study. After QPS-5 or QPS-50 intervention over the motor hot spot for the right first dorsal interosseous muscle (FDI), the subjects performed voluntary motor tasks (opening–closing right hand movements at 1 Hz for 1 min). We compared the time courses of MEP size between the conditions with and without voluntary movement. Results When the subjects moved their hands immediately after QPS, both QPS-5 and QPS-50 aftereffects were abolished. However, if they moved their hands at 20 min after QPS, the long-term aftereffects were preserved. Conclusions Voluntary hand movement applied after intervention influences QPS aftereffects, but the magnitude of the influence depends on the delay between QPS and the voluntary movement. Significance In the plasticity induction experiments, we should always be mindful of the fact that voluntary movement, including the target muscle, seriously influences the induced long-term effects of QPS. [ABSTRACT FROM AUTHOR]

Objective: Recent research indicates a task-specific neural coupling controlling cooperative hand movements reflected in bilateral electromyographic reflex responses in arm muscles following unilateral nerve stimulation. Reorganization of this mechanism was explored in post-stroke patients in this study. Methods: Electromyographic reflex responses in forearm muscles to unilateral electrical ulnar nerve stimulation were examined during cooperative and non-cooperative hand movements. Results: Stimulation of the unaffected arm during cooperative hand movements led to electromyographic responses in bilateral forearm muscles, similar to those seen in healthy subjects, while stimulation of the affected side was followed only by ipsilateral responses. No contralateral reflex responses could be evoked in severely affected patients. The presence of contralateral responses correlated with the clinical motor impairment as assessed by the Fugl-Meyer test. Conclusion: The observations suggest that after stroke an impaired processing of afferent input from the affected side leads to a defective neural coupling and is associated with a greater involvement of fiber tracts from the unaffected hemisphere during cooperative hand movements. [ABSTRACT FROM AUTHOR]

Highlights: [•] The hand function of non-neuropathic diabetic individuals was assessed using traditional hand function tests and instrumented handles. [•] Performance in two traditional hand function tests and maximum grip strength were not affected by diabetes. [•] Surprisingly, non-neuropathic diabetic individuals adopted lower safety margin than controls during a simple object manipulation. [ABSTRACT FROM AUTHOR]

Abstract: Objective: To evaluate the viability of MEG source reconstruction in the presence of large interference due to orthodontic material. Methods: We recorded the magnetic fields following a simple hand movement and following electrical stimulation of the median nerve (somatosensory evoked field –SEF). These two tasks were performed twice, once with and once without artificial dental artefacts. Temporal Signal Space Separation (tSSS) was applied to spatially filter the data and source reconstruction was performed according to standard procedures for pre-surgical mapping of eloquent cortex, applying dipole fitting to the SEF data and beamforming to the hand movement data. Results: Comparing the data with braces to the data without braces, the observed distances between the activations following hand movement in the two conditions were on average 6.4 and 4.5mm for the left and right hand, respectively, whereas the dipole localisation errors for the SEF were 4.1 and 5.4mm, respectively. Without tSSS it was generally not possible to obtain reliable dipole fit or beamforming results when wearing braces. Conclusion: We confirm that tSSS is a required and effective pre-processing step for data recorded with the Elekta-MEG system. Moreover, we have shown that even the presence of large interference from orthodontic material does not significantly alter the results from dipole localisation or beamformer analysis, provided the data are spatially filtered by tSSS. Significance: State-of-the-art signal processing techniques enable the use of MEG for pre-surgical evaluation in a much larger clinical population than previously thought possible. [Copyright &y& Elsevier]

Introduction Acupuncture is a therapeutic technique that is being used as an adjuvant to treatment in a variety of health-related disorders. However despite its increasing use in western countries, the underlying mechanisms are not fully understood. The aim of this study is to investigate the underlying neurophysiological mechanisms of acupuncture by examining the effect of real (verum) and sham acupuncture to the hand on the excitability of the motor cortex (M1) in healthy adults. A better understanding of the underlying mechanisms of acupuncture may improve the potential therapeutic application of acupuncture for neurological disorders in the future. Methods Healthy, right-handed, adults with no neurological or musckuloskeletal conditions participated in the study. Participants were randomised to receive verum or sham acupuncture to the Hegu acupoint of the hand on separate days, with a minimum 5 day washout. The intervention type was double-blinded, and the acupuncturist was not involved in data collection or analysis. Transcranial magnetic stimulation (TMS) was delivered to the left M1 and surface electromyography was used to record TMS-induced responses from the First Dorsal Interossues (FDI) and Adductor Digiti Minimi (ADM). Stimulus-response curves, short-intracortical inbhition (SICI-2 ms) and intracortical facilitaiton (ICF-15 ms) were measured before, during, immediately after needle removal, and 30 min after needle removal. Needling sensation questionnaires were administered after each session, and self-rated anxiety was assessed before, during and after needle removal. Results Relative to sham, verum acupuncture did not modulate corticomotor or intracortical excitability in either muscle across time (all P > 0.05). There were no differences in the severity of needling sensations between sessions (all P > 0.05), therefore sham park needle acupuncture was likely an adequate sham control. Conclusion There was little-to-no evidence that acupuncture to the Hegu acupoint of the hand modulated corticomotor or intracortical excitability to a hand muscle adjacent (FDI) and distant (ADM) to the acupoint. Previous research has reported neural changes after acupuncture using TMS, however these studies were of low-quality. The present study builds upon the previous literature by using an effective sham control, double-blinding, and records responses from the same limb being stimulated. The study findings suggest the putative effects of acupuncture are unlikely to be mediated by changes in motor cortex excitability. [ABSTRACT FROM AUTHOR]

Objective Conflicting theoretical models exist regarding the mechanism related to the ability of the Jendrassek maneuvre to reinforce reflex parameters. Our objective was to investigate if eventually inhibition of the spinal Ib motoneurone during remote muscle contraction would contribute to H-reflex enhancement. Method Soleus H-reflex from 26 healthy subjects was evoked on both sides by stimulating the tibial nerve at rest and during bilateral vigorous hadgrip. This procedure was repeated using paired stimulation at interstimulus intervals ranging from 2 ms to 15 ms. Mean conditioned H-wave amplitude expressed as a percentage of its unconditioned value (H-ratio) evoked during handgrip was compared with the H-ratio obtained at the same interstimulus interval at rest. Results The size of H-reflex evoked during handgrip was significantly higher then of that evoked at rest. The H-ratio value plotted against the interstimulus interval showed both at rest and during handgrip a similar decrease that was maximal at 5 ms and lasted less than 10 ms. Discussion The size of the conditioned H-reflex is determined by the balance between test Ia excitation and Ib inhibition elicited by the conditioning stimulus. According to our results the interneurones intercalated in pathways from Ib afferents retain their inhibitory effect on the alpha motoneurone during remote muscle contraction. Conclusion H-reflex enhancement during Jendrassek maneuvre is not due to inhibition of Ib interneurones. Significance Further studies are needed in order to test the role of other spinal circuits or descending drives that produce subthreshold excitation of alpha motoneurones by remote muscle contraction. [ABSTRACT FROM AUTHOR]

Adult patients presenting with slowly progressive hand weakness and wasting (HWW) without signs of upper motor neuron involvement and unconvincing cervical MRI signs of disk protrusion are a diagnostic challenge. Clinical and electrophysiological follow-up is needed to reach the most probable diagnosis. Objective We describe 4 adult patients who presented with HWW and involuntary tremor-like movements of the thumb. Methods We performed electrodiagnostic testing (EDX) two times, between 3 and 6 months and 12 and 24 months, after onset of symptoms. Cranial and cervical magnetic ressonance and laboratory workout were performed in all patients. Results Hyposthesia in the ulnar territory was the most common complaint that did not change between consultations. Muscle strength was decreased in fingers abduction-adduction movements. Thumb tremor was present and correlated with fasciculations in thenar and interossei muscles. The compound muscle and sensory nerve action potentials were reduced in median and ulnar nerves. We observed denervation signs in thenar and hypothenar muscles but not in biceps. The EDX signs did not change in the second examination. Conclusion Fasciculations in wasted hand muscles may induce involuntary movements mimicking tremor. Stabilization of symptoms and neurophysiological data favor spinal cord focal lesions over motor neuron disease. [ABSTRACT FROM AUTHOR]

Objective Transcranial magnetic stimulation (TMS) can be used to map the corticomotor representations of hand muscles in the precentral motor-cortex (PMC). The spatial peak of the corticomotor representations is often not located in the primary motor cortex (M1HAND), but shows an anterior shift towards the dorsal premotor cortex (PMd). Here we used magnetic resonance imaging (MRI) to test the hypothesis that the PMC shows different structural and functional properties in individuals with a clear “premotor” representation compared to individuals with a preponderant “primary-motor” representation of hand muscles. Methods MRI-measurements and neuronavigated-TMS were performed on twenty-four volunteers (mean age: 24.3 ± 0.9 SE, 12 women). Participants underwent structural MRI to evaluate cortical thickness and curvature of the PMC. We also performed fMRI to evaluate precentral functional activation in the hand-knob during a simple motor task. Sulcus-shape based TMS-mapping was used to obtain mediolateral and posterior-anterior corticomotor excitability profiles of the left abductor-digiti-minimi and first-dorsal-interosseus muscles. Results In 14 out of 24 individuals (58%), TMS mapping disclosed a clear spatial peak in the stimulation lines overlying the PMd, whereas the remaining 10 subjects (42%) showed maximal motor responses more posteriorly along M1HAND. During fMRI, the “premotor” group displayed a stronger task-related activation in the PMd relative to the “primary-motor” group ( p = 0.002). No difference between two groups was evident for curvature and cortical thickness. Conclusion The results confirm that many individuals have a more premotor corticomotor representation of small hand muscles when measured with TMS. This premotor phenotype in terms of corticomotor representation is associated with a stronger premotor activation during simple movements. This association supports the notion of two distinct functional phenotypes of corticomotor hand representations in human PMC: a primary motor and a premotor phenotype. [ABSTRACT FROM AUTHOR]

Introduction The effect of intracortical facilititation (ICF) is independent from hemispheric dominance and handedness (Bäumer et al., 2007). Short term training selectively increases excitability over the contralateral primary motor cortex (M1c) of the trained hand (e.g. Lotze et al., 2003). M1-excitability measurements after long-term training (several weeks) are rare but – to our knowledge – are even absent for ICF-parameters. Objectives To evaluate effects of ICF during a two week comprehensive period of training of the left hand in strongly right handed healthy participants. Materials and ethods Thirteen strongly right-handed healthy participants (23 ± 3.5 years; 6 women) underwent a two-week arm ability training (AAT) for their left, nondominant hand for one hour per day (Platz, 2004). Performance increase was expressed as percentual changes over time and averaged over all eight AAT-tasks. Focal TMS was delivered to the optimal scalp position for activation of the musculus abductor policis brevis (APB) of each hand using a figure-of-eight coil. Resting motor threshold (rMT) and intracortical facilitation (ICF; test stimulus intensity 120% rMT; conditioning stimulus 80% rMT; interstimulus interval 10 ms) were used as measures of corticomotor excitability. Results Training resulted in considerable improvement of the trained left (30 ± 3.5%) hand, but – to a lesser extent – also the non-trained right hand (18 ± 5.4%) performance. RMT was not altered over time. For ICF we found a strong time effect in ANOVA; but post hoc t-tests showed only a relevant decrease over time for the untrained side ( T (12) = 3.33; p = 0.006; Fig. 1). Conclusion Our study showed no significant changes in ICF for the trained hand side, but a decrease for the non trained hand’s motor cortex. It has been demonstrated that the interaction between an increase of unilateral movement and 10 h unilateral immobilization of the other hand is critical for excitability effects over M1c (Avanzino et al., 2011). We argue that interhemispheric changes induced by unilateral limb training of the non-dominant hand might be multifactorial; here we observed an increased interhemispheric balance in ICF after training the less experienced, and presumably in spontaneous behavior less intensively used hand. [ABSTRACT FROM AUTHOR]

Objective To investigate the relationship between changes of cortical hand motor representation and motor recovery of the affected hand in subacute stroke. Methods 17 patients with motor impairment of the affected hand were enrolled in an in-patient neurological rehabilitation program. Hand motor function tests (Wolf Motor Function Test, Action Research Arm Test) and the neurophysiological evaluations (resting motor threshold, motor evoked potentials, motor map area size, motor map area volume, motor map area location) were obtained from both hands and hemispheres at baseline, and two, four and six weeks of in-patient neurological rehabilitation. Results There was a wide spectrum of hand motor impairment at baseline and hand motor recovery over time. Hand motor function and recovery correlated significantly with (i) reduction of cortical excitability, (ii) reduction in size and volume of cortical hand motor representation and (iii) a medial and anterior shift of cortical hand motor representation within the contralesional hemisphere. Conclusion Recovery of motor function of the affected hand after stroke is accompanied by definite changes in excitability, size, volume and location of hand motor representation over the contralesional primary motor cortex. These measures may serve as surrogate markers for the outcome of hand motor rehabilitation after stroke. [ABSTRACT FROM AUTHOR]

We evaluated the role of cerebellum in defensive responses, by recording the Hand Blink Reflex (HBR) and modulating cerebellar activity with transcranial Direct Current Stimulation (tDCS). The active electrode was centered on the median line 2 cm below the inion and the return one over the right shoulder. Direct current was applied for 20 min with an intensity of 1.5 mA, both for cathodal and anodal stimulation. For the recording of HBR, we stimulated electrically the median nerve at the wrist and recorded EMG activity from the orbicularis oculi muscle bilaterally. Depending on the hand position respective to the face, we assessed four different conditions: “hand-far”, “hand-near” (eyes-open), “hand-side”, “hand-near” (eyes-closed). EMG signals were high-pass filtered (55 Hz), full-wave rectified, and averaged separately for the four conditions at the ipsilateral and contralateral recording sides. The anodal stimulation reduces the magnitude of the HBR, as measured by the Area Under the Curve (AUC), and increased the HBR latency in the “hand-side” and “hand-near” (eyes-closed) conditions (HBR magnitude: p = 0.004 and p < 0.0001; HBR latency: p = 0.023 and 0.002, respectively). These results support a critical role of the cerebellum in the defensive responses within the peripersonal space, thus selectively modulating defensive behavior when the visual feedback is missing. [ABSTRACT FROM AUTHOR]

Objective The aim of the study was to locate brain activation changes in stroke patients treated with Botulinum Toxin A (BoNT) for arm spasticity using functional MRI (fMRI). Methods Seven ischemic stroke patients (4 females, mean age 58.9) with severe spastic hand paralysis were studied. Spasticity was scored according to the modified Ashworth scale (MAS). FMRI was performed before (W0), 4 (W4) and 11 weeks (W11) after BoNT. Whole-brain fMRI data (1.5 T) were acquired during paced repetitive passive flexion/extension at the wrist of plegic limb alternating with rest. General Linear Model analysis used corrected cluster-wise p < 0.05. Results BoNT transiently lowered MAS in W4. In all sessions, fMRI activation of the ipsilesional sensorimotor cortex (contralateral to the moved hand) dominated. At W4, bilateral cerebellum transiently engaged. Paired contrasts demonstrated significant differences W4 > W0 (bilateral cerebellum, occipital and prefrontal cortex) and W4 > W11 (ipsilesional cerebellum, contralesional thalamus, bilateral premotor and posterior cingulate cortex). Conclusions Whole-brain activation patterns during BoNT treatment of post-stroke arm spasticity demonstrated changes both within and outside the classical sensorimotor system. Specific BoNT-related changes were revealed in the cerebellum. Supported by IGA Ministry of Health Czech Republic Grant NT13575 . [ABSTRACT FROM AUTHOR]

Objective We aimed to investigate hand movement onset (HMO), saccadic reaction time (SRT) and the interval between the initial saccade and the corrective saccade (ISI) during a reaching movement task. Methods Seven subjects, aged 29–39, participated in the study. We projected a scene of a penalty striker-goalkeeper combination and we asked participants to stop the ball (target) by using a linear joystick with the dominant hand. Two series of 20 trials at target velocities of 700 and 1400 pixels/s were performed. The eye-movement angle was 20° from initial fixation point. We measured eye saccade duration (SD) and peak velocity (PV), HMO latency, SRT and ISI in trials in which the subject stopped the ball. Results At low velocity, there were a similar amount of trials in which the hand was activated before and those in which it was activated after the eyes. At high target velocity, SRT and HMO had shorter time difference between them, PV was increased and ISI had a shorter duration while SD didn’t change. Conclusions The evaluation of the ISI is of interest for the assessment of increased qualitative workload. Motor hand preparation seems to occur concomitantly and sometimes before any afferent feedback from eye-saccade signals in eye-hand movement tasks. [ABSTRACT FROM AUTHOR]

Background: Carpal tunnel syndrome is rare in children but is a recognised complication of the mucopolysaccharidoses. Clinicians should have a low threshold of suspicion for carpal tunnel syndrome in this group as symptoms may be atypical or minimal, especially in those with intellectual disabilities secondary to mucopolysaccharidoses. If untreated, carpal tunnel syndrome can cause significant, potentially permanent loss of hand function. We present findings in 11 children with mucopolysaccharidoses and suspected median neuropathies at the wrist, and propose guidelines for screening for carpal tunnel syndrome in children with these disorders. Methods: Clinical and electrodiagnostic data of 11 children with confirmed mucopolysaccharidoses by enzymatic ± molecular testing, who were suspected on clinical grounds to have carpal tunnel syndrome, was reviewed. All subjects underwent motor and sensory conduction studies of bilateral median and ulnar nerves. The presence of carpal tunnel syndrome and its severity was determined. Subsequent details of intervention (s) and recurrence were noted. Results: Three children had Hurler syndrome (MPS I), five had Hunter syndrome (MPS II), one had Sanfilippo syndrome (MPS III) and two had Morquio syndrome (MPS IV). Seven had motor and three sensory features referable to median nerve compression. Nine of the eleven children (2/3 with MPS I, 5/5 with MPS II, 0/1 with MPS III, 2/2 with MPS IV) had median neuropathies at the wrist (eight bilateral, one unilateral), which were mild in three, moderate in five, and severe in one. Three children presented with symptoms at 5years age. Six underwent median nerve decompression. Four of these had recurrent symptoms several years after surgery. Recurrent carpal tunnel syndrome was confirmed on nerve conduction studies in two cases. To the best of our knowledge, this is the first report of carpal tunnel syndrome in MPS IV. Conclusion: Some children with mucopolysaccharidoses experience early development of at least moderately severe carpal tunnel syndrome. We recommend screening for median neuropathies at the wrist from age 5years for children with mucopolysaccharidoses, particularly types I, II and IV, regardless of whether they are symptomatic or asymptomatic of carpal tunnel syndrome and of the treatment received for their mucopolysaccharidosis. [ABSTRACT FROM AUTHOR]

Our aim was to evaluate whether the focal application of a vibratory stimulation on the skin may change the laser evoked potentials (LEPs) and the laser- pain to pulses delivered on the same cutaneous area. In 10 healthy volunteers, LEPs were recorded after stimulation of the radial and ulnar dorsal hand territories, bilaterally. After each LEP recording, the subjects were asked to rate the laser-pain according to a 100-point VAS. All subjects were evaluated in two different sessions in order to test both effective and sham vibratory stimulation. In each session, the experiment included 2 times: (1) LEPs were recorded without any conditioning vibratory stimulus, (2) LEPs were recorded during effective or sham vibratory stimulation within the right radial territory. No difference in N2/P2 amplitude changes was found between the effective and the sham vibratory stimulation. Also the subjective perception of pain was not influenced by the simultaneous vibratory (effective or sham) stimulation. Our negative results suggest that focal vibratory stimuli, currently used for motor rehabilitation, are not effective as analgesic physical treatment. [Copyright &y& Elsevier]

Transcranial direct current stimulation (TDCS) of primary motor cortex (M1) can transiently improve paretic hand function in chronic stroke. However, responses are variable so there is incentive to try to improve efficacy or to predict response in individual patients. Both excitatory (Anodal) stimulation of ipsilesional M1 and inhibitory (Cathodal) stimulation of contralesional M1 can speed simple reaction time. Here we tested whether combining these two effects simultaneously, by using a bilateral M1–M1 electrode montage, would improve efficacy. We tested the physiological efficacy of Bilateral, Anodal or Cathodal TDCS in changing motor evoked potentials (MEPs) in the healthy brain and their behavioural efficacy in changing reaction times with the paretic hand in chronic stroke. In addition, we aimed to identify clinical or neurochemical predictors of patients’ behavioural response to TDCS. There were three main findings: (1) Unlike Anodal and Cathodal TDCS, Bilateral M1–M1 TDCS (1mA, 20min) had no significant effect on MEPs in the healthy brain or on reaction time with the paretic hand in chronic stroke patients; (2) GABA levels in ipsilesional M1 predicted patients’ behavioural gains from Anodal TDCS; (3) Although patients were in the chronic phase, time since stroke (and its combination with Fugl-Meyer score) was a positive predictor of behavioural gain from Cathodal TDCS. These findings indicate the superiority of Anodal or Cathodal over Bilateral TDCS in changing motor corticospinal excitability in the healthy brain and in speeding reaction time in chronic stroke. The identified clinical and neurochemical markers of behavioural response should help to inform the optimization of TDCS delivery and to predict patient outcome variability in future TDCS intervention studies in chronic motor stroke. [Copyright &y& Elsevier]

Introduction: Impairment of motor function in Spinal cord injury (SCI) is associated with reduction in the excitability of motor cortical (M1) representations to muscles (Freund et al., 2011), while recovery is associated with representational plasticity (Jurkiewicz et al., 2010). Noninvasive brain stimulation (NBS) such as anodal transcranial direct current stimulation (atDCS) increases M1 excitability, and has beneficial effects on retention of motor skill training in both the healthy and chronic stroke survivor (Bastani and Jaberzadeh, 2012). However, sensory impairment may independently predict limits of recovery of functional independence (Kirshblum and O’Connor, 1998). Objective: This pilot study included incomplete tetraplegic spinal cord injured patients to examine whether the covariate of sensory impairment might account for the possible after effects of atDCS applied during simulated rehabilitation. Methods: 8 consenting right-handed outpatients at the London Spinal Cord Injury Centre, with partial impairment of non-dominant hand function (American Spinal Injury Association Impairment Scale (AIS) motor level C5-C7, C-D) were randomly allocated to ACTIVE or SHAM groups in a single-blinded RCT pilot study. Pre-assessment included standardised AIS scoring of upper limb sensory sparing (PINPRICK scoring). Subjects carried out practise of a novel, inclusive manual upper limb motor skill rehabilitation task (MSRT) developed to deliver the novel Task Productivity Rate (TPR) univariate skill measure derived from direct sampling of movement time and target accuracy. 45min continuous, repetitive MSRT training was applied from naïve baseline state on 3 consecutive days, with follow-up measures 7days afterwards, during the first 20min of which received either 20min ACTIVE anodal tDCS (1mA, 0.029mA/cm2) or a SHAM dosage to the non-dominant M1. TPR was obtained from the first 15min of practise in each session. Repeated measures ANOVA with covariate of PINPRICK scoring as measure of sensory impairment (ANCOVA) were applied to normalised data, with independent t-tests at the follow-up session. Results: The ACTIVE group retained a mean TPR improvement of 42% compared to 7% by SHAM which showed a non-significant trend to benefit of ACTIVE stimulation at follow-up t (6)=2.24, p =0.066. ANCOVA revealed significant (p <0.05) main effect of ACTIVE stimulation F (1,5)=12.9, interaction with practise time (F (3,15)=3.4, and between-groups effect at follow-up t (6)=3.16, p =0.025, r =0.625. PINPRICK was a significant independent factor F (1,5)=6.9, which remained stable over time F (3,15)=0.97, p =0.43. The independent factors did not interact (confirmatory ANCOVA F (1,4)=0.52, p =0.5). Conclusion: Adjunctive application of atDCS to M1 during rehabilitation may have imparted a lasting benefit compared to rehabilitation activity alone. But the covariate of sensory impairment (Pinprick score) independently modulated skill learning and retention scores. Because atDCS did not mitigate the negative effects of sensory impairment on skill acquisition, it is possible that atDCS boosts recovery of motor activation via un-masking of existing M1 connections rather than enhancing motor memory formation necessary for skills uptake (Reis and Fritsch, 2011). [ABSTRACT FROM AUTHOR]

Introduction: Transcranial direct current stimulation (tDCS) is a non-invasive method for modulation of brain activity and excitability. Anodal stimulation leads to an increase of excitability under the electrode, whereas cathodal tDCS decreases it (Nitsche et al., 2008). tDCS of the primary motor cortex has been shown its principal efficacy to improve motor functions (Nowak et al., 2009). However, not much is known about the effects of premotor tDCS on performance. In this study we investigated the influence of tDCS of the dorsal premotor cortex (PMd) on fine motor skills of the hand, referred to as dexterity. It was assessed by a newly-developed spring compression task (Valero-Cuevas et al., 2003). Methods: Two experiments were performed. In the first experiment 12 healthy persons received anodal tDCS to the primary motor cortex (M1) contralateral to the performing hand and sham stimulation to assess the sensitivity of the spring compression task for modulation by tDCS. In the second experiment, another group of 12 healthy persons participated in five sessions of stimulation comprising anodal and cathodal stimulation of the left and the right PMd and sham stimulation. The spring compression task was performed before and during stimulation. In this task, an unstable spring, held between the right thumb and index finger, is supposed to be compressed as much as possible without buckling. The force in the fingers, recorded by two sensors, serves as a measure of dexterity. tDCS-related performance alterations are expressed as percent change of the force during the stimulation compared to before stimulation. Results: tDCS over M1 in the experiment 1 as well as over the left, but not the right PMd in experiment 2 resulted in significant improvement of motor performance (Fig. 1). The effects of premotor tDCS were heterogeneous: Some participants benefitted from cathodal premotor stimulation (group 1), some from anodal (group 2) and others did not have a considerable effect (group 3). The effect of stimulation polarity correlated with variability (SD) of task performance and subjective task difficulty: participants of the group 2 had lowest variability and higher subjective task difficulty than group 2 (Fig. 2). Conclusions: The improvement of fine motor control during tDCS of the left dorsal premotor cortex makes this area a promising candidate for future investigations in the field. Acknowledgements: This study has been funded by Erik och Edith Fernströms stiftelse för medicinsk forskning and Stiftelsen Promobilia. [ABSTRACT FROM AUTHOR]