Different aspects of hand grip performance associated with structural connectivity of distinct sensorimotor networks in chronic stroke.

Knowledge regarding the neural origins of distinct upper extremity impairments may guide the choice of interventions to target neural structures responsible for specific impairments. This cross-sectional pilot study investigated whether different brain networks explain distinct aspects of hand grip performance in stroke survivors. In 22 chronic stroke survivors, hand grip performance was characterized as grip strength, reaction, relaxation times, and control of grip force magnitude and direction. In addition, their brain structural connectomes were constructed from diffusion tensor MRI. Prominent networks were identified based on a two-step factor analysis using the number of streamlines among brain regions relevant to sensorimotor function. We used regression models to estimate the predictive value of sensorimotor network connectivity for hand grip performance measures while controlling for stroke lesion volumes. Each hand grip performance measure correlated with the connectivity of distinct brain sensorimotor networks. These results suggest that different brain networks may be responsible for different aspects of hand grip performance, which leads to varying clinical presentations of upper extremity impairment following stroke. Understanding the brain network correlates for different hand grip performances may facilitate the development of personalized rehabilitation interventions to directly target the responsible brain network for specific impairments in individual patients, thus improving outcomes.

Bilateral Assessment of the Corticospinal Pathways of the Ankle Muscles Using Navigated Transcranial Magnetic Stimulation.

Distal leg muscles receive neural input from motor cortical areas via the corticospinal tract, which is one of the main motor descending pathway in humans and can be assessed using transcranial magnetic stimulation (TMS). Given the role of distal leg muscles in upright postural and dynamic tasks, such as walking, a growing research interest in the assessment and modulation of the corticospinal tracts relative to the function of these muscles has emerged in the last decade. However, methodological parameters used in previous work have varied across studies making the interpretation of results from cross-sectional and longitudinal studies less robust. Therefore, use of a standardized TMS protocol specific to the assessment of leg muscles' corticomotor response (CMR) will allow for direct comparison of results across studies and cohorts. The objective of this paper is to present a protocol that provides the flexibility to simultaneously assess the bilateral CMR of two main ankle antagonistic muscles, the tibialis anterior and soleus, using single pulse TMS with a neuronavigation system. The present protocol is applicable while the examined muscle is either fully relaxed or isometrically contracted at a defined percentage of maximum isometric voluntary contraction. Using each subject's structural MRI with the neuronavigation system ensures accurate and precise positioning of the coil over the leg cortical representations during assessment. Given the inconsistency in CMR derived measures, this protocol also describes a standardized calculation of these measures using automated algorithms. Though this protocol is not conducted during upright postural or dynamic tasks, it can be used to assess bilaterally any pair of leg muscles, either antagonistic or synergistic, in both neurologically intact and impaired subjects.

Changes in muscle coordination patterns induced by exposure to a viscous force field.

BACKGROUND: Robotic neurorehabilitation aims at promoting the recovery of lost function after neurological injury by leveraging strategies of motor learning. One important aspect of the rehabilitation process is the improvement of muscle coordination patterns, which can be drastically altered after stroke. However, it is not fully understood if and how robotic therapy can address these deficits. The aim of our study was to find how muscle coordination, analyzed from the perspective of motor modules, could change during motor adaptation to a dynamic environment generated by a haptic interface. METHODS: In our experiment we employed the traditional paradigm of exposure to a viscous force field to subjects that grasped the handle of an actuated joystick during a reaching movement (participants moved directly forward and back by 30 c m). EMG signals of ten muscles of the tested arm were recorded. We extracted motor modules from the pooled EMG data of all subjects and analyzed the muscle coordination patterns. RESULTS: We found that the participants reacted by using a coordination strategy that could be explained by a change in the activation of motor modules used during free motion and by two complementary modules. These complementary modules aggregated changes in muscle coordination, and evolved throughout the experiment eventually maintaining a comparable structure until the late phase of re-adaptation. CONCLUSIONS: This result suggests that motor adaptation induced by the interaction with a robotic device can lead to changes in the muscle coordination patterns of the subject.

Effects of stroke severity and training duration on locomotor recovery after stroke: a pilot study.

BACKGROUND: Locomotor training using partial body weight-supported treadmill (BWST) walking has been widely investigated for people after stroke, yet there remains a lack of evidence concerning the optimal training duration and the effect of locomotor impairment severity. Previous protocols have not emphasized the transfer of locomotor skills from the BWST environment to overground. OBJECTIVES: To assess the feasibility of a program combining locomotor training using BWST with task-specific overground training and to obtain pilot data on the effects of severity and training duration on recovery of locomotion. METHODS: Seven adults with chronic poststroke hemiparesis and gait speed less than 0.8 m/s were recruited to participate in a 12-week (36 session) locomotor training program. Each session comprised 20 to 30 minutes of training using BWST with manual assistance, followed by 10 to 15 minutes of overground training to transfer the skills trained in the BWST environment. Gait speed was the primary outcome measure. RESULTS: Six out of the 7 enrolled individuals completed the intervention program; 1 was withdrawn due to transportation difficulties affecting compliance with the training schedule. Four of the 6 participants had a functionally significant improvement in walking speed after 36 sessions, defined as having achieved a 0.4 m/s gait speed or greater for those with initial severe gait speed impairment (<0.4 m/s) or as having achieved a 0.8 m/s gait speed or greater for persons with initial moderate gait speed impairment (>or=0.4 m/s and <0.8 m/s). All participants improved in balance and distance walked over 6 minutes, and 5 of the 6 participants showed increases in their daily home and community step activity. CONCLUSIONS: A locomotor training program combining walking using BWST and manual assistance with overground practice is feasible for people with chronic poststroke hemiparesis and moderate or severe gait speed impairment. This intervention shows promise for achieving functionally significant improvements in walking speed.