Specificity of Sparing Effects with Cross-Education after Eccentric Training

Cross-education (CE) is the phenomenon that occurs after unilateral strength training whereby strength of the untrained contralateral limb is enhanced. A handful of studies have shown that CE can spare the loss of strength and size of an opposite immobilized limb, but specificity of these “sparing” effects is unknown. The purpose was to investigate specificity of CE sparing effects with immobilization. Sixteen participants were randomly assigned to a training (M=1, F=7; ht: 170.3±10.1 cm; wt: 77.2±19.2 kg) and control (M=2, F=6; ht: 169.3±8.5 cm; wt: 85.7±22.7 kg) group. Both groups wore a non-dominant forearm cast for four weeks. Two pre- and one post-testing session involved wrist flexors and extensors muscle thickness (ultrasound), eccentric (ECC), concentric (CON) and isometric (ISO) maximal voluntary contractions (dynamometer), electromyography (EMG) normalized to Mmax, and forearm muscle cross-sectional area (MCSA; peripheral quantitative computed tomography). Strength training was ECC wrist flexion 3 times per week. Group × time interactions for the immobilized and non-immobilized limbs revealed that only the training group showed strength preservation across all contractions in the wrist flexors of the immobilized limb (Training: pre=12.3±5.4 Nm, post=12.0±4.6 Nm vs. Control: pre=14.8±5.4 Nm, post=11.6±4.6 Nm; p=.04, η_p^2=.25), and increased wrist flexors strength of the non-immobilized limb (Training: pre=12.9±5.5 Nm, post=16.9±7.3 Nm vs Control: pre=14.9±5.5 Nm, post=13.8±7.3 Nm; p=.04, ηp2=.27). For MCSA there was a significant arm × time interaction for the control group only, p =.02, η_p^2 =.57, where the change in the left arm (pre: 35.2 ± 7.2 cm2; post: 34.4 ± 8.1 cm2; -2.3%) was different from the right arm (pre: 34.3 ± 7.7 cm2; post: 34.7 ± 8.0 cm2; 1.2%). Muscle thickness change differed between groups (Training: pre=3.3±0.5 cm, post=3.4±0.6 cm; control: pre=3.7±0.7 cm, post=3.7±0.6 cm) for the immobilized wrist flexors only (p=.01, η_p^2=.40). Analyses of normalized EMG data failed to reveal significant between group or co-activation differences regardless of muscle (flexors, extensors), task (flexion, extension) or contraction type (ECC, CON, ISO). Strength preservation was not specific to contraction type (p=.69, η_p^2=.03), yet sparing effects were specific to the trained muscle. The mechanisms of muscle size preservation remain unknown, but these data draw an important link between strength and muscle size sparing with CE and suggest that ECC training of the non-immobilized limb can preserve size of the immobilized contralateral homologous muscle and strength across multiple contraction types

High Force Unimanual Handgrip Contractions Increase Ipsilateral Sensorimotor Activation and Functional Connectivity

Imaging and brain stimulation studies seem to correct the classical understanding of how brain networks, rather than contralateral focal areas, control the generation of unimanual voluntary force. However, the scaling and hemispheric-specificity of network activation remain less understood. Using fMRI, we examined the effects of parametrically increasing right-handgrip force on activation and functional connectivity among the sensorimotor network bilaterally with 25%, 50%, and 75% maximal voluntary contractions (MVC). High force (75% MVC) unimanual handgrip contractions resulted in greater ipsilateral motor activation and functional connectivity with the contralateral hemisphere compared to a low force 25% MVC condition. The ipsilateral motor cortex activation and network strength correlated with relative handgrip force (% MVC). Increases in unimanual handgrip force resulted in greater ipsilateral sensorimotor activation and greater functional connectivity between hemispheres within the sensorimotor network. (C) 2020 IBRO. Published by Elsevier Ltd. All rights reserved

Repeated unilateral handgrip contractions alter functional connectivity and improve contralateral limb response times

In humans, motor learning is underpinned by changes in sensorimotor network functional connectivity (FC). Unilateral contractions increase FC in the ipsilateral primary motor cortex (M1) and supplementary motor area (SMA); areas involved in motor planning and execution of the contralateral hand. Therefore, unilateral contractions are a promising approach to augment motor performance in the contralateral hand. In a within-participant, randomized, cross-over design, 15 right-handed adults had two magnetic resonance imaging (MRI) sessions, where functional-MRI and MR-Spectroscopic Imaging were acquired before and after repeated right-hand contractions at either 5% or 50% maximum voluntary contraction (MVC). Before and after scanning, response times (RTs) were determined in both hands. Nine minutes of 50% MVC contractions resulted in decreased handgrip force in the contracting hand, and decreased RTs and increased handgrip force in the contralateral hand. This improved motor performance in the contralateral hand was supported by significant neural changes: increased FC between SMA-SMA and increased FC between right M1 and right Orbitofrontal Cortex. At a neurochemical level, the degree of GABA decline in left M1, left and right SMA correlated with subsequent behavioural improvements in the left-hand. These results support the use of repeated handgrip contractions as a potential modality for improving motor performance in the contralateral hand

Predicting Individual Treatment Response to rTMS for Motor Recovery After Stroke: A Review and the CanStim Perspective

BackgroundRehabilitation is critical for reducing stroke-related disability and improving quality-of-life post-stroke. Repetitive transcranial magnetic stimulation (rTMS), a non-invasive neuromodulation technique used as stand-alone or adjunct treatment to physiotherapy, may be of benefit for motor recovery in subgroups of stroke patients. The Canadian Platform for Trials in Non-Invasive Brain Stimulation (CanStim) seeks to advance the use of these techniques to improve post-stroke recovery through clinical trials and pre-clinical studies using standardized research protocols. Here, we review existing clinical trials for demographic, clinical, and neurobiological factors which may predict treatment response to identify knowledge gaps which need to be addressed before implementing these parameters for patient stratification in clinical trial protocols.ObjectiveTo provide a review of clinical rTMS trials of stroke recovery identifying factors associated with rTMS response in stroke patients with motor deficits and develop research perspectives for pre-clinical and clinical studies.MethodsA literature search was performed in PubMed, using the Boolean search terms stroke AND repetitive transcranial magnetic stimulation OR rTMS AND motor for studies investigating the use of rTMS for motor recovery in stroke patients at any recovery phase. A total of 1,676 articles were screened by two blinded raters, with 26 papers identified for inclusion in this review.ResultsMultiple possible factors associated with rTMS response were identified, including stroke location, cortical thickness, brain-derived neurotrophic factor (BDNF) genotype, initial stroke severity, and several imaging and clinical factors associated with a relatively preserved functional motor network of the ipsilesional hemisphere. Age, sex, and time post-stroke were generally not related to rTMS response. Factors associated with greater response were identified in studies of both excitatory ipsilesional and inhibitory contralesional rTMS. Heterogeneous study designs and contradictory data exemplify the need for greater protocol standardization and high-quality controlled trials.ConclusionClinical, brain structural and neurobiological factors have been identified as potential predictors for rTMS response in stroke patients with motor impairment. These factors can inform the design of future clinical trials, before being considered for optimization of individual rehabilitation therapy for stroke patients. Pre-clinical models for stroke recovery, specifically developed in a clinical context, may accelerate this process

Females exhibit smaller volumes of brain activation and lower inter-subject variability during motor tasks

Abstract Past work has shown that brain structure and function differ between females and males. Males have larger cortical and sub-cortical volume and surface area (both total and subregional), while females have greater cortical thickness in most brain regions. Functional differences are also reported in the literature, yet to date little work has systematically considered whether patterns of brain activity indexed with functional magnetic resonance imaging (fMRI) differ between females and males. The current study sought to remediate this issue by employing task-based whole brain motor mapping analyses using an openly available dataset. We tested differences in patterns of functional brain activity associated with 12 voluntary movement patterns in females versus males. Results suggest that females exhibited smaller volumes of brain activation across all 12 movement tasks, and lower patterns of variability in 10 of the 12 movements. We also observed that females had greater cortical thickness, which is in alignment with previous analyses of structural differences. Overall, these findings provide a basis for considering biological sex in future fMRI research and provide a foundation of understanding differences in how neurological pathologies present in females vs males

Repeated unilateral handgrip contractions alter functional connectivity and improve contralateral limb response times

Abstract In humans, motor learning is underpinned by changes in sensorimotor network functional connectivity (FC). Unilateral contractions increase FC in the ipsilateral primary motor cortex (M1) and supplementary motor area (SMA); areas involved in motor planning and execution of the contralateral hand. Therefore, unilateral contractions are a promising approach to augment motor performance in the contralateral hand. In a within-participant, randomized, cross-over design, 15 right-handed adults had two magnetic resonance imaging (MRI) sessions, where functional-MRI and MR-Spectroscopic Imaging were acquired before and after repeated right-hand contractions at either 5% or 50% maximum voluntary contraction (MVC). Before and after scanning, response times (RTs) were determined in both hands. Nine minutes of 50% MVC contractions resulted in decreased handgrip force in the contracting hand, and decreased RTs and increased handgrip force in the contralateral hand. This improved motor performance in the contralateral hand was supported by significant neural changes: increased FC between SMA-SMA and increased FC between right M1 and right Orbitofrontal Cortex. At a neurochemical level, the degree of GABA decline in left M1, left and right SMA correlated with subsequent behavioural improvements in the left-hand. These results support the use of repeated handgrip contractions as a potential modality for improving motor performance in the contralateral hand