Alana B. McCambridge

Mirror Symmetric Bimanual Movement Priming Can Increase Corticomotor Excitability and Enhance Motor Learning

Repetitive mirror symmetric bilateral upper limb may be a suitable priming technique for upper limb rehabilitation after stroke. Here we demonstrate neurophysiological and behavioural after-effects in healthy participants after priming with 20 minutes of repetitive active-passive bimanual wrist flexion and extension in a mirror symmetric pattern with respect to the body midline (MIR) compared to an control priming condition with alternating flexion-extension (ALT). Transcranial magnetic stimulation (TMS) indicated that corticomotor excitability (CME) of the passive hemisphere remained elevated compared to baseline for at least 30 minutes after MIR but not ALT, evidenced by an increase in the size of motor evoked potentials in ECR and FCR. Short and long-latency intracortical inhibition (SICI, LICI), short afferent inhibition (SAI) and interhemispheric inhibition (IHI) were also examined using pairs of stimuli. LICI differed between patterns, with less LICI after MIR compared with ALT, and an effect of pattern on IHI, with reduced IHI in passive FCR 15 minutes after MIR compared with ALT and baseline. There was no effect of pattern on SAI or FCR H-reflex. Similarly, SICI remained unchanged after 20 minutes of MIR. We then had participants complete a timed manual dexterity motor learning task with the passive hand during, immediately after, and 24 hours after MIR or control priming. The rate of task completion was faster with MIR priming compared to control conditions. Finally, ECR and FCR MEPs were examined within a pre-movement facilitation paradigm of wrist extension before and after MIR. ECR, but not FCR, MEPs were consistently facilitated before and after MIR, demonstrating no degradation of selective muscle activation. In summary, mirror symmetric active-passive bimanual movement increases CME and can enhance motor learning without degradation of muscle selectivity. These findings rationalise the use of mirror symmetric bimanual movement as a priming modality in post-stroke upper limb rehabilitation.

Cathodal transcranial direct current stimulation of the primary motor cortex improves selective muscle activation in the ipsilateral arm

Proximal upper limb muscles are represented bilaterally in primary motor cortex. Goal-directed upper limb movement requires precise control of proximal and distal agonist and antagonist muscles. Failure to suppress antagonist muscles can lead to abnormal movement patterns, such as those commonly experienced in the proximal upper limb after stroke. We examined whether noninvasive brain stimulation of primary motor cortex could be used to improve selective control of the ipsilateral proximal upper limb. Thirteen healthy participants performed isometric left elbow flexion by contracting biceps brachii (BB; agonist) and left forearm pronation (BB antagonist) before and after 20 min of cathodal transcranial direct current stimulation (c-tDCS) or sham tDCS of left M1. During the tasks, motor evoked potentials (MEPs) in left BB were acquired using single-pulse transcranial magnetic stimulation of right M1 150-270 ms before muscle contraction. As expected, left BB MEPs were facilitated before flexion and suppressed before pronation. After c-tDCS, left BB MEP amplitudes were reduced compared with sham stimulation, before pronation but not flexion, indicating that c-tDCS enhanced selective muscle activation of the ipsilateral BB in a task-specific manner. The potential for c-tDCS to improve BB antagonist control correlated with BB MEP amplitude for pronation relative to flexion, expressed as a selectivity ratio. This is the first demonstration that selective muscle activation in the proximal upper limb can be improved after c-tDCS of ipsilateral M1 and that the benefits of c-tDCS for selective muscle activation may be most effective in cases where activation strategies are already suboptimal. These findings may have relevance for the use of tDCS in rehabilitation after stroke.

Bridging the goal intention–action gap in rehabilitation: a study of if-then implementation intentions in neurorehabilitation

Abstract Purpose: To test the feasibility and acceptability of an implementation intention strategy (if-then plans) increasingly used in health psychology to bridge the goal intention–action gap in rehabilitation with people with neurological conditions who are experiencing difficulties with mobility. Methods: Twenty people with multiple sclerosis (MS) and stroke, randomised to an experimental and control group, set up to three mobility related goals with a physiotherapist. The experimental group also formulated if-then plans for every goal. Data collection: Focus groups and interviews with participants and therapists; Patient Activation Measure (PAM), 10-m walk test, Rivermead Mobility Index, self-efficacy, subjective health status, quality of life. Results: Qualitative data highlighted one main theme: Rehabilitation in context, encapsulating the usefulness of the if-then strategy in thinking about the patient in the context of complexity, the usefulness of home-based rehabilitation, and the perceived need for a few more sessions. Changes in walking speed were in the expected direction for both groups; PAM scores improved over 3 months in both groups. Conclusion: If-then plans were feasible and acceptable in bridging the goal intention–action gap in rehabilitation with people with MS and stroke, who are experiencing difficulties with mobility. This approach can now be adapted and trialled further in a definitive study. Implications for Rehabilitation Goal planning in rehabilitation necessitates specific strategies that help people engage in goal-related tasks. If-then plans aim to support people to deal more effectively with self-regulatory problems that might undermine goal striving and have been found to be effective in health promotion and health behaviour change. This feasibility study with people with a stroke and multiple sclerosis has demonstrated that if-then plans are feasible and acceptable to patients and physiotherapists in supporting goal-directed behaviour.

A dissociation between propriospinal facilitation and inhibition after bilateral transcranial direct current stimulation.

Propriospinal premotoneurons (PN) are essential for accurate control of the upper limb. They receive bilateral input from premotor (PM) and primary motor (M1) cortices. In humans, excitability of PNs can be estimated from motor-evoked potentials (MEPs) by pairing a descending volley using transcranial magnetic stimulation (TMS) to summate with an ascending volley from peripheral nerve stimulation at the C3-C4 level of the spinal cord. Transcranial direct current stimulation (tDCS) alters excitability of cortical and subcortical areas. A recent study demonstrated that cathodal tDCS can suppress facilitatory (FAC) and inhibitory (INH) components of PN excitability, presumably via effects on corticoreticulospinal neurons (Bradnam LV, Stinear CM, Lewis GN, Byblow WD. J Neurophysiol 103: 2382-2389, 2010). The present study investigated the effects of bilateral tDCS with healthy subjects. The cathode was placed over left dorsal PM or M1 and the anode over right M1 in separate sessions (PM-M1, M1-M1, or Sham). TMS of right M1 elicited MEPs in left biceps brachii across a range of TMS intensities chosen to examine PN-mediated FAC and INH. Conditioning was applied using median nerve stimulation with an interstimulus interval that coincided with TMS and peripheral volleys summating at the C3-C4 level. All participants showed FAC at TMS intensities near active motor threshold and INH at slightly higher intensities. After tDCS, FAC was reduced for M1-M1 compared with Sham but not after PM-M1 stimulation. Contrary to an earlier study with cathodal tDCS, INH was unchanged across all sessions. The difference between these and earlier findings may relate to dual- vs. single-hemisphere M1 stimulation. M1-M1 tDCS may be a useful adjuvant to techniques that aim to reduce upper limb impairment after stroke.

Bridging the gap between goal intentions and actions: a systematic review in patient populations

Abstract Purpose: To evaluate the evidence for the effectiveness of if-then implementation intentions (if-then plans) in adult patient populations. Outcomes of interest included adherence, goal pursuit and physical health outcomes. Methods: Keywords were used to search electronic databases without date or language restrictions (up to 30 April 2014). Studies were included if they (1) concerned a patient population; (2) used if-then plans as a sole intervention or as part of treatment, therapy or rehabilitation; (3) if they were randomised controlled trials. The PEDro scale was used to evaluate study quality. Guidance as set out by the Cochrane Collaboration was used. Two reviewers independently extracted data, discrepancies were discussed and if required referred to a third reviewer. Results: In total, 18 of the 2141 articles were identified as potentially relevant and four studies of people with epilepsy, chronic back pain, stroke and obesity met the inclusion criteria. People who form if-then plans achieved better outcomes on epilepsy and stroke medication adherence and physical capacity than controls. Conclusions: Of the four studies that used an if-then plan, only one (people with epilepsy) looked at the intervention as a stand-alone strategy. Further research needs to explore if this simple approach improves rehabilitation outcomes and is a helpful and feasible strategy for people experiencing disabilities. Implications for Rehabilitation Steps involved in achieving goals, such as doing exercises or completing other goal related tasks, can be compromised for people with chronic health conditions particularly resulting from difficulties in self-regulating behaviour. If-then plans are implementation intention tools aimed at supporting people to deal more effectively with self-regulatory problems that might undermine goal striving and goal attainment, and have been found to be effective in health promotion and health behaviour change. This systematic literature review identified four studies completed with patient populations, with three demonstrating effectiveness. If-then plans provide an opportunity for clinicians to develop better ways of implementing rehabilitation.

Revisiting interhemispheric imbalance in chronic stroke: a tDCS study

OBJECTIVE Chronic stroke patients with moderate-severe motor impairment may have an increased reliance on contralesional vs ipsilesional motor areas to control the paretic arm. We hypothesised that increasing contralesional excitability with anodal transcranial direct current stimulation (a-tDCS) would benefit motor performance in patients with moderate-severe impairment. METHODS Ten patients with motor impairment at the chronic stage after stroke received a-tDCS, cathodal (c-tDCS) and sham with the target electrode over contralesional motor cortex (M1). Motor performance was quantified from the circularity and size of planar movements made with the paretic arm. Contralateral and ipsilateral corticospinal excitability was inferred using transcranial magnetic stimulation. Corticospinal tract integrity and basal GABA concentration were assessed with magnetic resonance imaging and spectroscopy. RESULTS Anodal tDCS increased contralesional corticomotor excitability evident from motor evoked potentials in both wrist extensors (both P<0.043). Cathodal tDCS did not affect corticomotor excitability (P>0.37). The effect of tDCS on motor performance with the paretic limb was negatively associated with ipsilesional GABA concentration after c-tDCS (P=0.001). CONCLUSIONS Further investigation of noninvasive brain stimulation protocols that facilitate contralesional M1 is warranted. SIGNIFICANCE The inter-hemispheric imbalance model of stroke recovery may not apply to patients with more severe impairment.

S63. Cerebellar stimulation for adults with cervical dystonia: A tDCS study

Introduction Cervical dystonia (CD) is characterized by painful, involuntary twisting of the neck, and sometimes tremor. Unfortunately, treatment options for CD are limited and the underlying pathophysiology is not well understood. Recent evidence implicates cerebellar dysfunction may play a role in the development of CD symptoms. Non-invasive brain stimulation is able to modulate neural excitability of the cerebellum. Methods The present study examined the effect of five consecutive days of anodal transcranial direct current stimulation (tDCS) over the cerebellum of adults with CD (2 mA, 20 min). Patients received five sessions of anodal tDCS and sham tDCS in a randomised, cross-over design that was double-blinded. During tDCS, patients performed a motor imagery task (first 10 min) and a real movement task (last 10 min). We hypothesised that anodal tDCS would improve patient’s clinical features and modulate neural excitability of the cerebellum. Clinical features were examined using the TWSTRS2, CDQ-24, cervical range of motion, and visual analogue scales of pain. Behavioural outcomes were assessed using a motor learning finger tracking task. Neural excitability was inferred using eye-blink conditioning to examine cerebellar excitability and single-pulse transcranial magnetic stimulation (TMS) over the motor cortex to examine corticomotor excitability and intracortical inhibition. Motor evoked potentials (MEP) and cortical silent periods (cSP) were recorded bilaterally from the upper trapezius (UT) and first dorsal interosseous (FDI) muscles. All dependent measures were assessed on day-1 and day-5 of the intervention, and follow up questionnaires were completed one and four weeks later. There was a minimum washout period of 5 weeks between treatment blocks, and patients undergoing Botox were tested 4 weeks post injections. Results The study is in the late stages of data collection and analysis ( n  = 14 patients enrolled, 8 males). Conclusion The outcome of this research may lead to the development of an alternative or adjuvant intervention for the management of CD and improve our understanding of the dysfunctional neurophysiology in this condition.

F138. The effect of velum and sham acupuncture on corticomotor excitability in healthy adults

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.

Propriospinal cutaneous-induced EMG suppression is unaltered by anodal tDCS of healthy motor cortex

OBJECTIVE Cervical propriospinal premotoneurons (PN) relay descending motor commands and integrate peripheral afferent feedback. Effects of anodal transcranial direct current stimulation (a-tDCS) on propriospinal excitability in the upper limbs are unknown. METHODS Healthy right-handed adults received a-tDCS or sham tDCS over primary motor cortex (M1) at 1mA (Experiment 1, n=18) or 2mA current intensity (Experiment 2, n=15). Propriospinal excitability was assessed by suppression of background electromyography (EMG) in extensor carpi radialis (ECR) from electrical stimulation of the superficial radial nerve during bilateral (Experiment 1 and 2) or unilateral (Experiment 2 only) activation of the left and/or right ECR. EMG suppression could be attributed to an early propriospinal component and late cortical component. Motor evoked potentials (MEP) were obtained as a manipulation check. RESULTS Before tDCS, propriospinal-mediated cutaneous-induced suppression was present in each arm for early and late components. ECR MEP amplitude increased after 1mA, but not 2mA, a-tDCS. Neither 1mA nor 2mA a-tDCS modulated either component of ipsilateral or contralateral propriospinal excitability during bilateral or unilateral tasks. CONCLUSIONS Propriospinal-mediated cutaneous-induced suppression was not modulated by a-tDCS in healthy adults. SIGNIFICANCE Reporting non-significant findings is paramount for the development of clinically-relevant tDCS protocols.

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.