Matthew P. Malcolm

Reliability of motor cortex transcranial magnetic stimulation in four muscle representations

OBJECTIVE Motor cortex plasticity may underlie motor recovery after stroke. Numerous studies have used transcranial magnetic stimulation (TMS) to investigate motor system plasticity. However, research on the reliability of TMS measures of motor cortex organization and excitability is limited. We sought to test the reliability of these TMS measurements. METHODS Twenty healthy volunteers were tested twice over a two-week period using TMS to determine motor threshold, map topography, and stimulus-response curves for first dorsal interosseous (FDI), abductor pollicis brevis (APB), extensor digitorum communis (EDC), and flexor carpi radialis (FCR) muscles. RESULTS We found moderate to good test-retest reliability TMS measurements of motor threshold (ICC=0.90-0.97), map area (ICC=0.63-0.86) and location (ICC=0.69-0.86), and stimulus-response curves (ICC=0.60-0.83). CONCLUSIONS TMS assessments of motor representation size, location, and excitability are generally reliable measures, although their reliability may vary according to the muscle under investigation. SIGNIFICANCE These results suggest that TMS measurements of motor cortex function are reliable enough to be potentially useful in investigation of motor system plasticity.

Repetitive transcranial magnetic stimulation as an adjunct to constraint-induced therapy: an exploratory randomized controlled trial.

Malcolm MP, Triggs WJ, Light KE, Gonzalez Rothi LJ, Wu S, Reid K, Nadeau SE: Repetitive transcranial magnetic stimulation as an adjunct to constraint-induced therapy: an exploratory randomized controlled trial. Am J Phys Med Rehabil 2007;86:707–715. Objective:To test the potential adjuvant effect of repetitive transcranial magnetic stimulation (rTMS) on motor learning in a group of stroke survivors undergoing constraint-induced therapy (CIT) for upper-limb hemiparesis. Design:This was a prospective randomized, double-blind, sham-controlled, parallel group study. Nineteen individuals, one or more years poststroke, were randomized to either a rTMS + CIT (n = 9) or a sham rTMS + CIT (n = 10) group and participated in the 2-wk intervention. Results:Regardless of group assignment, participants demonstrated significant gains on the primary outcome measures: the Wolf Motor Function Test (WMFT) and the Motor Activity Log (MAL)–Amount of Use, and on secondary outcome measures including the Box and Block Test (BBT) and the MAL–How Well. Participants receiving rTMS failed to show differential improvement on either primary outcome measure. Conclusions:Although this study provided further evidence that even relatively brief sessions of CIT can have a substantial effect, it provided no support for adjuvant use of rTMS.

Does Provision of Extrinsic Feedback Result in Improved Motor Learning in the Upper Limb Poststroke? A Systematic Review of the Evidence

Background. Recovery of the upper limb (UL) after a stroke occurs well into the chronic stage. Stroke survivors can benefit from adaptive plasticity to improve UL movement through motor relearning. The provision of feedback has been shown to decrease the use of compensatory UL movement patterns. However, the effectiveness of feedback in improving UL motor recovery after a stroke has not yet been systematically reviewed. Objective.The objective of this review was to systematically examine the role of extrinsic feedback on implicit motor learning after stroke, focusing on UL movement and functional recovery. Results. The authors retrieved 9 studies that examined the role of feedback on UL motor recovery. Of these, 6 were randomized controlled trials (RCTs), 1 was a single-subject design, 1 was a pre—post design, and 1 was a cohort study. The studies were rated on the basis of Sackett’s levels of evidence and PEDro (Physiotherapy Evidence Database) scores for RCTs. Levels of evidence were limited (level 2b) for UL motor learning of the less-affected extremity and strong (level 1a) for the more-affected extremity. Discussion and conclusions. The results suggest that people with stroke may be capable of using extrinsic feedback for implicit motor learning and improving UL motor recovery. Emergent questions regarding the advantages of using different media for feedback delivery and the optimal type and schedule of feedback to enhance motor learning in patient populations still need to be addressed.

Rhythmic auditory-motor entrainment improves hemiparetic arm kinematics during reaching movements: a pilot study.

Abstract Purpose: Recovery of skilled upper limb movement remains a critical focus of rehabilitation in individuals post stroke. Conventional treatments, however, have demonstrated limited capability to produce substantial improvements in poststroke quality of movement. Recently, rhythmic auditory stimulation (RAS) has emerged as efficacious in improving and normalizing limb movements in neurologically impaired populations. This pilot study examined changes in pre- to post-RAS reach kinematics and functional outcomes in survivors of stroke. Method: Five individuals in the chronic poststroke phase participated in a 2-week program of RAS training. Kinematic reaching variables were trunk, shoulder, and elbow segment contribution; movement time; and reach velocity. Functional outcomes were the Wolf Motor Function Test, Motor Activity Log, and Fugl-Meyer Assessment. Results: Post-RAS assessment of reaching kinematics revealed a significant (p < .05) decrease in compensatory trunk movement, increase in shoulder flexion, and a slight increase in elbow extension. Movement time and velocity significantly improved post RAS. Significant gains were observed on all functional assessments. Conclusions: Post RAS, participants demonstrated substantial decreases in compensatory reaching movements. These changes in motor control strategy were paralleled by gains in functional abilities, suggesting that reduced reliance on compensatory movements may translate to improved performance of daily activities.

Reliability and validity of the BTE-Primus grip tool.

This study was designed to examine the reliability and validity of the newly designed grip tool of the Baltimore Therapeutic Equipment (BTE)-Primus and to investigate the effects of body position (sit versus stand), handedness, and fatigue on grip strength. The subjects performed maximal grip strength tests using the Jamar dynamometer and the BTE-Primus. Intraclass correlation coefficients were calculated for test-retest reliability and criterion-related validity. A repeated measures analysis of covariance was conducted to reveal differences in grip strength between instruments, body positions, hands, and sessions. The BTE-Primus grip tool was found to be reliable (r = 0.97 to 0.98) and valid (r = 0.95 to 0.96). There were no significant differences in grip strength scores between the Jamar and the BTE-Primus or between sitting and standing. Grip strength scores of the right hand were significantly greater than those of the left hand, and grip strength scores in the first session were significantly greater than those in the second session. The results of this study indicate that clinicians can use the BTE-Primus grip attachment at the second handle setting and know that is reliable, valid, and comparable to the second-handle setting of the Jamar dynamometer.

A pneumatic vibrotactile stimulation device for fMRI

Mapping the functional response of the somatosensory cortex is useful both for characterizing normal brain activity and for determining the functional integrity of damaged cortex compromised by stroke or other neurological insults. A variety of stimulators have been used to produce somatosensory cortex activation in functional brain imaging, including brushes and swabs operated manually, pneumatically and mechanically powered mechanical vibrators, air puffs, and vibrating ceramic piezoelectric wafers and benders. A closed‐system, pneumatically driven rubber diaphragm is reported that overcomes many of the limitations of existing vibrotactile devices and produces robust sensory cortex activation in an fMRI experiment. Magn Reson Med 51:640–643, 2004.

Reliability of transcranial magnetic stimulation for mapping swallowing musculature in the human motor cortex.

OBJECTIVE Although transcranial magnetic stimulation (TMS) has been widely used to study motor cortex organization and excitability, the reliability of this technique has not been thoroughly investigated. Furthermore, previous reports of TMS reliability have been restricted to upper limb musculature. We sought to determine the test-retest reliability for TMS mapping of motor representations for swallowing musculature. METHODS Twenty healthy volunteers were tested twice over two weeks using TMS to determine motor threshold, map area, map volume, maximal MEP site location and maximal MEP site size for the suprahyoid complex and pharyngeal musculature. RESULTS Good test-retest reliability was found in both swallowing muscle sites for the following test parameters: motor map area, maximal MEP site location: lateral coordinate, maximal MEP site size and motor threshold (ICC=0.76-0.98). Moderate reliability was observed for motor map volume and maximal MEP site location: anterior-posterior coordinate (ICC=0.68-0.74). CONCLUSIONS TMS assessments of motor representation size, location and excitability appear to be highly reproducible, although the reliability of these measures may vary according to the specific muscle under investigation. SIGNIFICANCE These works provide much needed psychometric data to validate the use of TMS to assess the cortical representation of swallowing musculature.

Functional repetitive transcranial magnetic stimulation increases motor cortex excitability in survivors of stroke.

OBJECTIVE To determine if repetitive transcranial magnetic stimulation (rTMS) applied to the motor cortex with simultaneous voluntary muscle activation, termed functional-rTMS, will promote greater neuronal excitability changes and neural plasticity than passive-rTMS in survivors of stroke. METHODS Eighteen stroke survivors were randomized into functional-rTMS (EMG-triggered rTMS) or passive-rTMS (rTMS only; control) conditions. Measures of short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF), force steadiness (coefficient of variation, CV) at 10% of maximum voluntary contraction, and pinch task muscle activity were assessed before and after rTMS. Functional-rTMS required subjects to exceed a muscle activation threshold to trigger each rTMS train; the passive-rTMS group received rTMS while relaxed. RESULTS Significant interactions (time × condition) were observed in abductor pollicis brevis (APB) SICI, APB ICF, CV of force, and APB muscle activity. Functional-rTMS decreased APB SICI (p < 0.05) and increased ICF (p < 0.05) after stimulation, whereas passive-rTMS decreased APB muscle activity (p < 0.01) and decreased CV of force (p < 0.05). No changes were observed in FDI measures (EMG, ICF, SICI). CONCLUSION(S) Functional-rTMS increased motor cortex excitability, i.e., less SICI and more ICF for the APB muscle. Passive stimulation significantly reduced APB muscle activity and improved steadiness. SIGNIFICANCE Functional-rTMS promoted greater excitability changes and selectively modulated agonist muscle activity.

Repetitive transcranial magnetic stimulation interrupts phase synchronization during rhythmic motor entrainment

Rhythmic stimuli delivered through the auditory system can facilitate improved motor control following a motor impairment. The synchronization of movement to rhythmic auditory cues is characterized by quick, stable coupling of motor responses to rhythmic auditory cues. The exact neural sites responsible for this transformation of auditory input into timed rhythmic motor output are not clear. Neuroimaging studies have identified left ventral premotor cortex (vPMC) and left superior temporal-parietal (STP) activation during rhythmic auditory-motor synchronization. To investigate brain areas necessary for different types of rhythmic auditory-motor synchronization, we delivered repetitive transcranial magnetic stimulation (rTMS) to 15 healthy individuals prior to a rhythmic-auditory tapping task. Subthreshold rTMS was administered separately to the left vPMC and STP at a frequency of 0.9Hz for 15 min. Phase synchronization error (difference between auditory stimulus and response onsets) significantly increased after rTMS to STP as compared to baseline. Synchronization error also increased after rTMS to vPMC as compared to baseline, but not significantly. Absolute period error, (absolute difference between metronome interval and response interval) was not affected by rTMS. The significant effect of rTMS at the STP expands upon previous imaging research, suggesting that this area is part of the network responsible for rhythmic auditory-motor synchronization. The effect of rTMS on phase synchronization, but not period synchronization suggests these are separate neural processes controlled by different neural networks.

Elbow Extension Predicts Motor Impairment and Performance after Stroke

Background and Purpose. Kinematic motion analysis has helped to characterize poststroke reaching strategies with the hemiparetic arm. However, the relationships between reaching strategy and performance on common functional outcome measures remain unclear. Methods. Thirty-five participants were tested for motor performance and motor impairment using the Wolf Motor Function Test (time and functional ability measure) and Fugl-Meyer assessment, respectively. Kinematic motion analysis of a forward reaching paradigm provided potential predictors of reaching strategy including shoulder flexion, elbow extension, and trunk displacement. A stepwise linear regression model with three potential predictors was used in addition to Pearson-product moment correlations. Results. Kinematic analysis of elbow extension predicted performance on both the Wolf Motor Function Test and Fugl-Meyer assessment. Shoulder flexion and trunk displacement did not significantly predict functional or reaching time outcomes. The Wolf Motor Function Test and the Fugl-Meyer assessment were highly correlated. Conclusions. The ability to incorporate elbow extension during reach is a significant predictor of motor performance and hemiparetic arm motor capacity after stroke.