Corticospinal responses following strength training: a systematic review and meta-analysis

Abstract

Strength-training results in changes in skeletal muscle, however, changes in the central nervous system also occur. Over the last 15 years, non-invasive brain stimulation techniques, such as transcranial magnetic stimulation, have been used to study the neural adaptations to strength-training. This review explored the hypothesis that the neural adaptations to strength-training may be due to changes in corticospinal excitability and inhibition and, such changes, contribute to the gain in strength following strength-training. A systematic review, according to PRISMA guidelines, identified studies by database searching, hand-searching and citation tracking between January 1990 and the first week of February 2017. Methodological quality of included studies was determined using the Downs and Black quality index. Data were synthesised and interpreted from meta-analysis. Nineteen studies investigating the corticospinal responses following strength-training were included. Meta-analysis found that strength-training increased strength (standardized mean difference [SMD] 0.84, 95% CI 0.55 to 1.13), decreased short-interval intracortical-inhibition (SMD -1.00, 95% CI -1.84 to -0.17) and decreased the cortical silent period (SMD -0.66, 95% CI -1.00 to -0.32). Strength-training had no effect on motor threshold (SMD -0.12, 95% CI -0.49 to 0.25), but a borderline effect for increased corticospinal excitability (SMD 0.27, 95% CI 0.00 to 0.54). In untrained healthy participants, the corticospinal response to strength-training is characterised by reduced intracortical inhibition and cortical silent period duration, rather than changes in corticospinal excitability. These data demonstrate that strength-training targets intracortical inhibitory networks within the primary motor cortex (M1) and corticospinal pathway, characterizing an important neural adaptation to strength training.

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Ipsilateral corticotectal projections from the primary, premotor and supplementary motor cortical areas in adult macaque monkeys: a quantitative anterograde tracing study

Abstract

The corticotectal projection from cortical motor areas is one of several descending pathways involved in the indirect control of spinal motoneurons. In non-human primates, previous studies reported that cortical projections to the superior colliculus originated from the premotor cortex and the primary motor cortex, whereas no projection originated from the supplementary motor area. The aim of the present study was to investigate and compare the properties of corticotectal projections originating from these three cortical motor areas in intact adult macaques (n=9). The anterograde tracer BDA was injected into one of these cortical areas in each animal. Individual axonal boutons, both en passant and terminaux, were charted and counted in the different layers of the ipsilateral superior colliculus. The data confirmed the presence of strong corticotectal projections from the premotor cortex. A new observation was that strong corticotectal projections were also found to originate from the supplementary motor area (its proper division). The corticotectal projection from the primary motor cortex was quantitatively less strong than that from either the premotor or supplementary motor areas. The corticotectal projection from each motor area was directed mainly to the deep layer of the superior colliculus, although its intermediate layer was also a consistent target of fairly dense terminations. The strong corticotectal projections from non-primary motor areas are in position to influence the preparation and planning of voluntary movements.

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Low-Dose Fractionated Irradiation Promotes Axonal Regeneration Beyond Reactive Gliosis and Facilitates Locomotor Function Recovery After Spinal Cord Injury in Beagle Dogs

Abstract

Injury to the adult central nervous system (CNS) results in the formation of glial scar tissues. Glial scar-induced failure of regenerative axon pathfinding may limit axon regrowth beyond the lesion site and cause incorrect reinnervation and dystrophic appearance of stalled growth after CNS trauma. Glial scars also upregulate chondroitin sulfate proteoglycans (CSPGs) and expression of proinflammatory factor(s) that form a barrier to axonal regeneration. Therefore, interventions for glial scarring are an attractive strategy for augmenting axonal sprouting and regeneration and overcoming the physical and molecular barriers impeding functional repair. The glial reaction occurs shortly after spinal cord injury (SCI) and can persist for days or weeks with upregulation of cell cycle proteins. In this study, we utilized Beagle dogs to establish a preclinical SCI model and examine the efficacy of low-dose fractionated irradiation (LDI) treatment, which was performed once a day for 14 days (2 Gy per dose, 28 Gy in total). LDI is a stable method for suppressing cell activation and proliferation through interference in the cell cycle. Our results demonstrated that LDI could reduce astrocyte and microglia activation/proliferation and attenuate CSPGs and IL-1β expression. LDI also promoted and provided a pathway for long-distance axon regeneration beyond the lesion site, induced reinnervation of axonal targets, and restored locomotor function after SCI in Beagle dogs. Taken together, our findings suggest that LDI would be a promising therapeutic strategy for targeting glial scarring, promoting axon regeneration, and facilitating reconstruction of functional circuits after SCI.

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The Effects of Dynamical Synapses on Firing Rate Activity: A Spiking Neural Network Model

Abstract

Accumulating evidence relates the fine-tuning of synaptic maturation and regulation of neural network activity to several key factors, including GABA_A signaling and a lateral spread length between neighboring neurons (i.e. local connectivity). Furthermore, a number of studies consider Short-Term synaptic Plasticity (STP) as an essential element in the instant modification of synaptic efficacy in the neuronal network and in modulating responses to sustained ranges of external Poisson Input Frequency (IF). Nevertheless, evaluating the firing activity in response to the dynamical interaction between STP (triggered by ranges of IF), and these key parameters in vitro remains elusive. Therefore, we designed a Spiking Neural Network (SNN) model in which we incorporated the following parameters: local density of arbor essences and a lateral spread length between neighboring neurons. We also created several network scenarios based on these key parameters. Then, we implemented two classes of STP: (1) Short-Term synaptic Depression (STD), and (2) Short-Term synaptic Facilitation (STF). Each class has two differential forms based on the parametric value of its synaptic time constant (either for depressing or facilitating synapses). Lastly, we compared the neural firing responses before and after the treatment with STP. We found that dynamical synapses(STP) have a critical differential role on evaluating, and modulating the firing rate activity in each network scenario. Moreover, we investigated the impact of changing the balance between excitation (E) / inhibition (I) on stabilizing this firing activity.

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Issue Cover (September 2017)

Cover image by Dr. Natalie Doig (MRC Brain Network Dynamics Unit, Department of Pharmacology, Oxford). The cover image is of a frontal section of mouse brain showing many regions of the basal ganglia. The section was triple-immunostained to reveal tyrosine hydroxylase (TH; cyan), parvalbumin (PV; green) and choline acetyltransferase (magenta).

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Systematic Standardized and Individualized Assessment of Masticatory Cycles Using Electromagnetic 3D Articulography and Computer Scripts

Masticatory movements are studied for decades in odontology; a better understanding of them could improve dental treatments. The aim of this study was to describe an innovative, accurate, and systematic method of analyzing masticatory cycles, generating comparable quantitative data. The masticatory cycles of 5 volunteers (Class I, 19 ± 1.7 years) without articular or dental occlusion problems were evaluated using 3D electromagnetic articulography supported by MATLAB software. The method allows the trajectory morphology of the set of chewing cycles to be analyzed from different views and angles. It was also possible to individualize the trajectory of each cycle providing accurate quantitative data, such as number of cycles, cycle areas in frontal view, and the ratio between each cycle area and the frontal mandibular border movement area. There was a moderate negative correlation (−0.61) between the area and the number of cycles: the greater the cycle area, the smaller the number of repetitions. Finally it was possible to evaluate the area of the cycles through time, which did not reveal a standardized behavior. The proposed method provided reproducible, intelligible, and accurate quantitative and graphical data, suggesting that it is promising and may be applied in different clinical situations and treatments.

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Liquid-Cell Electron Microscopy of Adsorbed Polymers

Individual macromolecules of polystyrene sulfonate and poly(ethylene oxide) are visualized with nanometer resolution using transmission electron microscopy (TEM) imaging of aqueous solutions with and without added salt, trapped in liquid pockets between creased graphene sheets. Successful imaging with 0.3 s per frame is enabled by the sluggish mobility of the adsorbed molecules. This study finds, validating others, that an advantage of this graphene liquid-cell approach is apparently to retard sample degradation from incident electrons, in addition to minimizing background scattering because graphene windows are atomically thin. Its new application here to polymers devoid of metal-ion labeling allows the projected sizes and conformational fluctuations of adsorbed molecules and adsorption–desorption events to be analyzed. Confirming the identification of the observed objects, this study reports statistical analysis of datasets of hundreds of images for times up to 100 s, with variation of the chemical makeup of the polymer, the molecular weight of the polymer, and the salt concentration. This observation of discrete polymer molecules in solution environment may be useful generally, as the findings are obtained using an ordinary TEM microscope, whose kind is available to many researchers routinely.

Direct real-space investigation of adsorbed polymer dynamics, with single-polymer resolution using conventional transmission electron microscopy (TEM) (transmission liquid microscope) and graphene liquid cell, gives a time series of polymer images which enable statistical analysis of projected sizes, conformational rearrangements, and adsorption dynamics. This demonstrates the capability to image polymers in solution using a conventional TEM.

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