Siobhan M Schabrun

Evidence for the retraining of sensation after stroke: a systematic review

Objective: Retraining of sensory function following stroke is frequently overlooked in rehabilitation protocols despite more than 60% of patients presenting with sensory deficits. Methods to train sensory function include both passive and active training protocols. Here we examined the volume and quality of the evidence available for both passive and active sensory training following stroke. In addition, we aimed to quantify the effect of sensory training on impairment and function. Data sources: Databases searched included MEDLINE, AMED, CINAHL, Academic search elite, Scopus and the Cochrane library. Unpublished articles were identified using a search engine. Review methods: Studies utilizing passive or active sensory training paradigms post stroke were identified. Methodological quality was examined using the National Health and Medical Research Council hierarchy of evidence and the McMaster University critical appraisal tool. Results: Fourteen studies met the inclusion criteria; 8 examined passive and 6 active sensory training. Methodological quality scores ranged from 11 to 18.5 (maximum 20). Meta-analysis was performed using three studies examining hand function, demonstrating a moderate effect in favour of passive sensory training. Other studies were unable to be pooled due to heterogeneity of measures or insufficient data. Conclusion: Meta-analyses and single studies offer some support for the effectiveness of passive sensory training in relation to sensory impairment and motor function. However, empirical evidence for active sensory training is limited. Further high-quality studies with greater statistical power and meaningful clinical measures are required in order to accurately determine the effectiveness of sensory retraining following stroke.

Peripheral electrical stimulation to induce cortical plasticity: A systematic review of stimulus parameters

Peripheral electrical stimulation (ES) is commonly used as an intervention to facilitate movement and relieve pain in a variety of conditions. It is widely accepted that ES induces rapid plastic change in the motor cortex. This leads to the exciting possibility that ES could be used to drive cortical plasticity in movement disorders, such as stroke, and conditions where pain affects motor control. This paper aimed to critically review the literature to determine which parameters induced cortical plasticity in healthy individuals using ES. A literature search located papers that assessed plasticity in the primary motor cortex of adult humans. Studies that evaluated plasticity using change in the amplitude of potentials evoked by transcranial magnetic stimulation of the motor cortex were included. Details from each study including sample size, ES parameters and reported findings were extracted and compared. Where data were available, Cohens standardised mean differences (SMD) were calculated. Nineteen studies were located. Of the parameters evaluated, variation of the intensity of peripheral ES appeared to have the most consistent effect on modulation of excitability of corticomotor pathway to stimulated muscles. There was a trend for stimulation above motor threshold to increase excitability (SMD 0.79 mV, CI -0.10 to 1.64). Stimulation below motor threshold, but sufficient to induce sensory perception, produced conflicting results. Further studies with consistent methodology and larger subject numbers are needed before definitive conclusions can be drawn. There also appeared to be a time effect. That is, longer periods of ES induced more sustained changes in cortical excitability. There is insufficient evidence to determine the effect of other stimulation parameters such as frequency and waveform. Further research is needed to confirm whether modulation of these parameters affects plastic change.

A checklist for assessing the methodological quality of studies using transcranial magnetic stimulation to study the motor system: An international consensus study

In the last decade transcranial magnetic stimulation (TMS) has been the subject of more than 20,000 original research articles. Despite this popularity, TMS responses are known to be highly variable and this variability can impact on interpretation of research findings. There are no guidelines regarding the factors that should be reported and/or controlled in TMS studies. This study aimed to develop a checklist to be recommended to evaluate the methodology and reporting of studies that use single or paired pulse TMS to study the motor system. A two round international web-based Delphi study was conducted. Panellists rated the importance of a number of subject, methodological and analytical factors to be reported and/or controlled in studies that use single or paired pulse TMS to study the motor system. Twenty-seven items for single pulse studies and 30 items for paired pulse studies were included in the final checklist. Eight items related to subjects (e.g. age, gender), 21 to methodology (e.g. coil type, stimulus intensity) and two to analysis (e.g. size of the unconditioned motor evoked potential). The checklist is recommended for inclusion when submitting manuscripts for publication to ensure transparency of reporting and could also be used to critically appraise previously published work. It is envisaged that factors could be added and deleted from the checklist on the basis of future research. Use of the TMS methodological checklist should improve the quality of data collection and reporting in TMS studies of the motor system.

Texting and walking: strategies for postural control and implications for safety.

There are concerns about the safety of texting while walking. Although evidence of negative effects of mobile phone use on gait is scarce, cognitive distraction, altered mechanical demands, and the reduced visual field associated with texting are likely to have an impact. In 26 healthy individuals we examined the effect of mobile phone use on gait. Individuals walked at a comfortable pace in a straight line over a distance of ∼8.5 m while; 1) walking without the use of a phone, 2) reading text on a mobile phone, or 3) typing text on a mobile phone. Gait performance was evaluated using a three-dimensional movement analysis system. In comparison with normal waking, when participants read or wrote text messages they walked with: greater absolute lateral foot position from one stride to the next; slower speed; greater rotation range of motion (ROM) of the head with respect to global space; the head held in a flexed position; more in-phase motion of the thorax and head in all planes, less motion between thorax and head (neck ROM); and more tightly organized coordination in lateral flexion and rotation directions. While writing text, participants walked slower, deviated more from a straight line and used less neck ROM than reading text. Although the arms and head moved with the thorax to reduce relative motion of the phone and facilitate reading and texting, movement of the head in global space increased and this could negatively impact the balance system. Texting, and to a lesser extent reading, modify gait performance. Texting or reading on a mobile phone may pose an additional risk to safety for pedestrians navigating obstacles or crossing the road.

Normalizing Motor Cortex Representations in Focal Hand Dystonia

Task-specific focal dystonia is thought to have a neurological basis where stereotypical synchronous inputs and maladaptive plasticity play a role. As afferent input is a powerful driver of cortical reorganization, we propose that a period of asynchronous afferent stimulation may reverse maladaptive cortical changes and alleviate symptoms. Using transcranial magnetic stimulation (TMS), 3 hand muscles were mapped in 10 dystonics and 10 healthy controls. Mapping occurred before and after 1 h of nonassociative stimulation (NAS) to first dorsal interosseous (FDI) and abductor pollicis brevis (APB). Participants performed grip lift, handwriting, and cyclic drawing before and after NAS. Prior to NAS, dystonics had larger maps, and the centers of gravity (CoGs) of the FDI and APB maps were closer together. Dystonics demonstrated impairments in grip-lift, handwriting, and cyclic drawing tasks. Following NAS, map size was reduced in all muscles in dystonic participants and FDI and APB CoGs moved further apart. Among dystonics, NAS produced a reduction in movement variability during cyclic drawing. Thus, 1 h of NAS can reduce the magnitude, and increase the separation, of TMS representational maps. We suggest that these changes reflect some normalization of the representational abnormalities seen in focal dystonia and provide initial, limited evidence that such changes are associated with improvements in circle drawing.

Corticospinal excitability is dependent on the parameters of peripheral electric stimulation : a preliminary study

OBJECTIVE To evaluate the effect of 6 electric stimulation paradigms on corticospinal excitability. DESIGN Using a same subject pre-post test design, transcranial magnetic stimulation (TMS) was used to measure the responsiveness of corticomotor pathway to biceps and triceps brachii muscles before and after 30 minutes of electric stimulation over the biceps brachii. Six different electric stimulation paradigms were applied in random order, at least 3 days apart. SETTING Motor control research laboratory. PARTICIPANTS Healthy subjects (N=10; 5 women, 5 men; mean age ± SD, 26 ± 3.6y). INTERVENTIONS Six different electric stimulation paradigms with varied stimulus amplitude, frequency, and ramp settings. MAIN OUTCOME MEASURE Amplitudes of TMS-induced motor evoked potentials at biceps and triceps brachii normalized to maximal M-wave amplitudes. RESULTS Electric stimulation delivered at stimulus amplitude sufficient to evoke a sensory response at both 10 Hz and 100 Hz, and stimulus amplitude to create a noxious response at 10 Hz decreased corticomotor responsiveness (all P<0.01). Stimulation sufficient to induce a motor contraction (30 Hz) applied in a ramped pattern to mimic a voluntary activation increased corticomotor responsiveness (P=0.002), whereas constant low- and high-intensity motor stimulation at 10 Hz did not. Corticomotor excitability changes were similar for both the stimulated muscle and its antagonist. CONCLUSIONS Stimulus amplitude (intensity) and the nature (muscle flicker vs contraction) of motor stimulation have a significant impact on changes in corticospinal excitability induced by electric stimulation. Here, we demonstrate that peripheral electric stimulation at stimulus amplitude to create a sensory response reduces corticomotor responsiveness. Conversely, stimulus amplitude to create a motor response increases corticomotor responsiveness, but only the parameters that create a motor response that mimics a voluntary muscle contraction.

Targeting Chronic Recurrent Low Back Pain From the Top-down and the Bottom-up: A Combined Transcranial Direct Current Stimulation and Peripheral Electrical Stimulation Intervention

BACKGROUND Mechanisms such as neural sensitization and maladaptive cortical organization provide novel targets for therapy in chronic recurrent low back pain (CLBP). OBJECTIVE We investigated the effect of a transcranial direct current stimulation (tDCS) and peripheral electrical stimulation (PES) treatment on pain, cortical organization, sensitization and sensory function in CLBP. METHODS Using a placebo-controlled crossover design, 16 individuals received four treatments in separate sessions: (i) anodal tDCS/PES; (ii) anodal tDCS/sham PES; (iii) sham tDCS/PES; or (iv) sham tDCS/sham PES. Pain was assessed at baseline, immediately following, and at 1 and 3 days after treatment. Motor cortical organization, sensitization and sensory function were measured before and immediately after treatment. RESULTS Combined tDCS/PES reduced pain and sensitization, normalized motor cortical organization and improved sensory function. The reduction in pain was greater in individuals with more pronounced sensitization. Applied alone, tDCS or PES also reduced pain. However, with the exception of improved sensory function and reduced map volume following PES, clinical and neurophysiological outcomes were unaltered by tDCS or PES applied separately. No changes were observed following sham treatment. CONCLUSION Our data suggest a combined tDCS/PES intervention more effectively improves CLBP symptoms and mechanisms of cortical organization and sensitization, than either intervention applied alone or a sham control.

Primary Sensory and Motor Cortex Excitability Are Co- Modulated in Response to Peripheral Electrical Nerve Stimulation

Peripheral electrical stimulation (PES) is a common clinical technique known to induce changes in corticomotor excitability; PES applied to induce a tetanic motor contraction increases, and PES at sub-motor threshold (sensory) intensities decreases, corticomotor excitability. Understanding of the mechanisms underlying these opposite changes in corticomotor excitability remains elusive. Modulation of primary sensory cortex (S1) excitability could underlie altered corticomotor excitability with PES. Here we examined whether changes in primary sensory (S1) and motor (M1) cortex excitability follow the same time-course when PES is applied using identical stimulus parameters. Corticomotor excitability was measured using transcranial magnetic stimulation (TMS) and sensory cortex excitability using somatosensory evoked potentials (SEPs) before and after 30 min of PES to right abductor pollicis brevis (APB). Two PES paradigms were tested in separate sessions; PES sufficient to induce a tetanic motor contraction (30–50 Hz; strong motor intensity) and PES at sub motor-threshold intensity (100 Hz). PES applied to induce strong activation of APB increased the size of the N20-P25 component, thought to reflect sensory processing at cortical level, and increased corticomotor excitability. PES at sensory intensity decreased the size of the P25-N33 component and reduced corticomotor excitability. A positive correlation was observed between the changes in amplitude of the cortical SEP components and corticomotor excitability following sensory and motor PES. Sensory PES also increased the sub-cortical P14-N20 SEP component. These findings provide evidence that PES results in co-modulation of S1 and M1 excitability, possibly due to cortico-cortical projections between S1 and M1. This mechanism may underpin changes in corticomotor excitability in response to afferent input generated by PES.

Effects of whole body vibration on strength and functional mobility in multiple sclerosis

The aim of this study was to examine the effectiveness of regular whole body vibration (WBV) training on lower limb muscle strength and functional mobility in individuals with multiple sclerosis. A single subject experimental design was replicated on three subjects. Phases included a 4-week baseline phase without intervention, 6 weeks of twice weekly WBV intervention on a VibroGym apparatus, and a 4-week baseline phase without intervention. During all phases, strength of the ankle plantarflexors and knee extensors was assessed twice weekly with the Nicholas Manual Muscle tester and functional mobility with the Timed Up and Go test. All subjects improved significantly in plantarflexor strength (p<0.05). One subject improved significantly in knee extensor strength bilaterally and one subject in the weaker leg. Two subjects improved significantly in functional mobility. These improvements in strength and mobility were maintained in the final baseline phase. In conclusion, regular WBV training can improve lower limb strength and mobility in some individuals with multiple sclerosis. Individuals who do not perform any other exercise, are in a moderate stage of disease progression, and have a more intensive exercise protocol in conjunction with WBV seem to benefit most. However, further high-quality studies are needed.

Novel adaptations in motor cortical maps: the relation to persistent elbow pain.

INTRODUCTION Unilateral elbow pain results in sensorimotor dysfunction that is frequently bilateral, affects local and remote upper limb muscles, and persists beyond resolution of local tendon symptoms. These characteristics suggest supraspinal involvement. Here, we investigated 1) the excitability and organization of the M1 representation of the wrist extensor muscles and 2) the relation between M1 changes and clinical outcomes in lateral epicondylalgia (LE) (n = 11) and healthy control subjects (n = 11). METHODS Transcranial magnetic stimulation was used to map the M1 representation of the extensor carpi radialis brevis (ECRB) and extensor digitorum (ED). RESULTS The cortical representations of ECRB and ED were more excitable, and the centers of gravity for the two muscles were located closer together in LE than that in healthy controls. Increased ECRB excitability and closer location of the center of gravity were associated with higher pain severity at rest and/or in the preceding 6 months. A novel finding was a reduced number of discrete peaks in the representations of ECRB and ED in participants with LE compared with that in healthy controls. CONCLUSIONS This finding may have broad implications for the control of the wrist extensor muscles in LE. These data provide evidence that cortical organization may be maladaptive in LE and suggest that reorganization may be associated with persistence/recurrence of pain.