Modulation of the cutaneous silent period in the upper-limb with whole-body instability

poster abstractThe silent period (CSP) induced by cutaneous electrical stimulation of the digits has been shown to be task-dependent, at least in the grasping muscles of the hand. However, it is unknown if the CSP is adaptable throughout muscles of the entire upper limb, in particular when the task requirements are substantially altered. The purpose of the present study was to examine the characteristics of the CSP in several upper limb muscles when introducing increased whole-body instability. The CSP was evoked in 10 healthy individuals with electrical stimulation of digit II of the right hand when the subjects were seated, standing, or standing on a wobble board while maintaining a background elbow extension contraction with the triceps brachii of ~5% of maximal voluntary contraction (MVC) strength. The first excitatory response (E1), first inhibitory response (CSP), and second excitatory response (E2) were quantified as the percent increase from baseline and by their individual durations. The results showed that the level of CSP suppression significantly decreased (52.3 ± 7.7% to 66.2 ± 13.2% of baseline, p = 0.019) and there was a trend for the CSP duration to decrease (p = 0.053) in the triceps brachii during the wobble board task. For the wobble board task the amount of cutaneous afferent inhibition of EMG activity in the triceps brachii decreased; which is proposed to be due to differential weighting of cutaneous feedback relative to the corticospinal drive, most likely due to presynaptic inhibition, to meet the demands of the unstable task

Differential processing of nociceptive input within upper limb muscles

The cutaneous silent period is an inhibitory evoked response that demonstrates a wide variety of responses in muscles of the human upper limb. Classically, the cutaneous silent period results in a characteristic muscle pattern of extensor inhibition and flexor facilitation within the upper limb, in the presence of nociceptive input. The aims of the current study were: 1) to primarily investigate the presence and characteristics of the cutaneous silent period response across multiple extensor and flexor muscles of the upper limb, and 2) to secondarily investigate the influence of stimulation site on this nociceptive reflex response. It was hypothesized that the cutaneous silent period would be present in all muscles, regardless of role (flexion/extension) or the stimulation site. Twenty-two healthy, university-age adults (14 males; 8 females; 23 ± 5 yrs) participated in the study. Testing consisted of three different stimulation sites (Digit II, V, and II+III nociceptive stimulation) during a low intensity, sustained muscle contraction, in which, 7 upper limb muscles were monitored via surface EMG recording electrodes. Distal muscles of the upper limb presented with the earliest reflex onset times, longest reflex duration, and lowest level of EMG suppression when compared to the more proximal muscles, regardless of extensor/flexor role. Additionally, the greatest overall inhibitory influence was expressed within the distal muscles. In conclusion, the present study provides a new level of refinement within the current understanding of the spinal organization associated with nociceptive input processing and the associated motor control of the upper limb. Subsequently, these results have further implications on the impact of nociception on supraspinal processing

Determinants of Fatigue in the Biceps Brachii During Blood Flow Restriction Training

poster abstractTraining loads of 60% - 80% of maximum are traditionally recommended for increasing muscular strength. Lifting lighter loads (~20% of 1RM) with concomitant blood flow restriction (BFR) can also increase muscle strength. It is unknown if adaptation with BFR is limited to the muscle or also due to changes in the nervous system. We examined changes in the output of the motor cortex and the muscle with stimulation, when subjects perform 1.) Training with light loads, 2.) Training with light loads with BFR, and 3.) Training with moderate loads. 5 subjects completed three training sessions with the elbow flexor muscles. Maximal strength was measured before and after each training session. Voluntary activation was tested with cortical stimulation (TMS) and with electrical stimulation of the biceps during additional MVCs. Subjects trained with a block of 4 isometric contractions at 20% MVC (120s, 60s, 60s, 60s durations) or at 60% MVC (40s, 20s, 20s, 20s durations). Fatigue (% decrease in MVC after training) was similar between 20% with BFR and 60% conditions (18.6% and 16%) and less in the 20% without BFR condition (9.7%). Cortical voluntary activation decreased similarly between the 20% BFR and 60% conditions (-3.6% and -3.3%) and showed less change with 20% without BFR (-1.8%). Alternatively, with electrical stimulation of the muscle, both 20% training conditions showed a decline in voluntary activation (-3.1% and -5.15), while voluntary activation increased by 8% after the 60% condition. Similar levels of fatigue occur at different contraction intensities when BFR is applied during the lighter contraction. Both 20% with BFR and 60% loading causes deficits in cortical activation, though the limiting factor in the 20% BFR condition is a decrease in activation of the muscle directly, while in the 60% contraction it is due to an inability to drive the motorneuron pool sufficiently

Cutaneous Silent Period Characteristics are Dependent on the Organization of Upper Limb Muscles

abstractCutaneous silent periods (CSPs) are inhibitory spinal reflexes mediated by small diameter A-δ fibers, serving to protect the body from harmful stimuli (Leis et al., 1992; Kofler, 2003). Currently, CSPs are believed to only inhibit the extensor muscles of the upper limb halting motions such as reaching, while exciting flexor muscles to withdraw the limb. The present study sought to determine if CSPs could be evoked in both extensor and flexor muscles of the upper limb, thereby providing further insight into the organization of the spinal circuitry associated with this reflex. 22 subjects performed contractions with seven muscles from the hand, forearm, upper arm, and shoulder while muscle activity was recorded with electromyography. Subjects were electrically stimulated (10x perceptual threshold) with 20 individual pulses delivered to each digit II (radial nerve) and digit V (ulnar nerve) of the right hand during each contraction. Results demonstrated significant main effects (p<0.001) across muscles for the key dependent variables of the CSP: onsets (F[6,21] = 15.42, p <0.001), durations (F[6,21] = 65.39, p <0.001), and % of suppression (F[6,21] = 91, p <0.001), similarly for both nerves stimulated. Distal muscles presented with the earliest onset times, longest duration of inhibition, and largest amount of inhibition. Moving proximally, the onset times became later with duration and the amount of inhibition decreasing. Linear regressions showed that the distance of the muscle from the spinal cord (cm) was a significant predictor of the duration (digit II r2 = 0.43; digit V r2 = 0.46) and amount of inhibition (digit II r2 = 0.51; digit V r2 = 0.48). The results demonstrate the occurrence of CSPs throughout the upper limb, with the greatest inhibition of distal muscles, leading us to hypothesize that the corticospinal tract, specifically direct cortico-motorneuronal connections, are directly influenced by the inhibitory input

Cortical Representation and Excitability Increases for a Thenar Muscle Mediate Improvement in Short-Term Cellular Phone Text Messaging Ability

Cortical representations expand during skilled motor learning. We studied a unique model of motor learning with cellular phone texting, where the thumbs are used exclusively to interact with the device and the prominence of use can be seen where 3200 text messages are exchanged a month in the 18-24 age demographic. The purpose of the present study was to examine the motor cortex representation and input-output (IO) recruitment curves of the abductor pollicis brevis (APB) muscle of the thumb and the ADM muscle with transcranial magnetic stimulation (TMS), relative to individuals' texting abilities and short-term texting practice. Eighteen individuals performed a functional texting task (FTT) where we scored their texting speed and accuracy. TMS was then used to examine the cortical volumes and areas of activity in the two muscles and IO curves were constructed to measure excitability. Subjects also performed a 10-min practice texting task, after which we repeated the cortical measures. There were no associations between the cortical measures and the FTT scores before practice. However, after practice the APB cortical map expanded and excitability increased, whereas the ADM map constricted. The increase in the active cortical areas in APB correlated with the improvement in the FTT score. Based on the homogenous group of subjects that were already good at texting, we conclude that the cortical representations and excitability for the thumb muscle were already enlarged and more receptive to changes with short-term practice, as noted by the increase in FTT performance after 10-min of practice

Cortical Representation and Excitability Increases for a Thenar Muscle Mediate Improvement in Short-Term Cellular Phone Text Messaging Ability

Cortical representations expand during skilled motor learning. We studied a unique model of motor learning with cellular phone texting, where the thumbs are used exclusively to interact with the device and the prominence of use can be seen where 3200 text messages are exchanged a month in the 18–24 age demographic. The purpose of the present study was to examine the motor cortex representation and input–output (IO) recruitment curves of the abductor pollicis brevis (APB) muscle of the thumb and the ADM muscle with transcranial magnetic stimulation (TMS), relative to individuals’ texting abilities and short-term texting practice. Eighteen individuals performed a functional texting task (FTT) where we scored their texting speed and accuracy. TMS was then used to examine the cortical volumes and areas of activity in the two muscles and IO curves were constructed to measure excitability. Subjects also performed a 10-min practice texting task, after which we repeated the cortical measures. There were no associations between the cortical measures and the FTT scores before practice. However, after practice the APB cortical map expanded and excitability increased, whereas the ADM map constricted. The increase in the active cortical areas in APB correlated with the improvement in the FTT score. Based on the homogenous group of subjects that were already good at texting, we conclude that the cortical representations and excitability for the thumb muscle were already enlarged and more receptive to changes with short-term practice, as noted by the increase in FTT performance after 10-min of practice

Ke Ao: A Low-Cost 1U CubeSat for Aerospace Education and Research in Hawaii

The Ke Ao satellite is a low-cost 1U CubeSat designed and developed by an undergraduate team of engineering students at the University of Hawaii at Manoa (UHM) in collaboration with the Hawaii Space Flight Laboratory (HSFL). The primary goal of the mission is to take one or more pictures from space and automatically identify the Hawaiian Islands using Machine Learning Algorithms - this will demonstrate improved onboard operational autonomy in space. A secondary goal of this project is to promote Aerospace Education and Workforce training in Hawaii. The Ke Ao project was inspired by the Hiapo CubeSat initiative of the Hawaii Science and Technology Museum as a unique platform used to provide engaging meaningful hands-on STEM curriculum for Hawaii students K-12. The realization that low-cost flight hardware, in the order of ～$10k, is practically non-existent, and therefore the barrier to launch a flight-capable CubeSat is still high for small organizations and schools with low budgets. The Ke Ao project started in the Fall of 2019 with the Vertically Integrated Project (VIP) Aerospace Technologies with Electrical, Mechanical, and Computer Science Engineering Students at UH and continued to be facilitated under the Mechanical Engineering Senior Design Course within the College of Engineering throughout the year of 2020. The project was impacted by the global COVID-19 pandemic but this enabled the student team to improve on the design and simulations. Hiapo and Ke Ao also inspired the NASA Artemis CubeSat Kit project being developed at the HSFL. The Artemis CubeSat Kit will be used as an educational tool for teaching aerospace and distribution in the public domain. The development of these three CubeSats allowed for synergistic development and multipurpose designs and gave the students a wide breadth of design experiences. This paper will expand on the design and development for the main objectives for Ke Ao (1) take one or more pictures of the Hawaiian Islands from space; (2) cost shall be no more than$10,000 with built parts; and (3) launch-ready via the NASA CSLI application and requirements. To address these objectives Ke Ao uses spaceflight capable but low-cost hardware flown in previous CubeSat missions and consists of seven primary subsystems: Attitude Determination and Control System, Communications, Electrical Power Systems, On-Board Computer and Flight Software, Payload, Structure and Mechanisms, and Thermal Control Systems. Ke Ao will use onboard magnetic torquers to control the attitude of the payload and take pictures of the Hawaiian Islands. The data will be transmitted to the HSFL ground stations in Hawaii and through the SatNOGS ground station network across the World. Ke Ao’s mission and primary goals are in line with the 2018 NASA Strategic Plan’s Strategic Objective 3.3 to Inspire and Engage the Public in Aeronautics, Space, and Science and contribute to the Nation’s science literacy

Chondrogenic and Gliogenic Subpopulations of Neural Crest Play Distinct Roles during the Assembly of Epibranchial Ganglia

In vertebrates, the sensory neurons of the epibranchial (EB) ganglia transmit somatosensory signals from the periphery to the CNS. These ganglia are formed during embryogenesis by the convergence and condensation of two distinct populations of precursors: placode-derived neuroblasts and neural crest- (NC) derived glial precursors. In addition to the gliogenic crest, chondrogenic NC migrates into the pharyngeal arches, which lie in close proximity to the EB placodes and ganglia. Here, we examine the respective roles of these two distinct NC-derived populations during development of the EB ganglia using zebrafish morphant and mutants that lack one or both of these NC populations. Our analyses of mutant and morphant zebrafish that exhibit deficiencies in chondrogenic NC at early stages reveal a distinct requirement for this NC subpopulation during early EB ganglion assembly and segmentation. Furthermore, restoration of wildtype chondrogenic NC in one of these mutants, prdm1a, is sufficient to restore ganglion formation, indicating a specific requirement of the chondrogenic NC for EB ganglia assembly. By contrast, analysis of the sox10 mutant, which lacks gliogenic NC, reveals that the initial assembly of ganglia is not affected. However, during later stages of development, EB ganglia are dispersed in the sox10 mutant, suggesting that glia are required to maintain normal EB ganglion morphology. These results highlight novel roles for two subpopulations of NC cells in the formation and maintenance of EB ganglia: chondrogenic NC promotes the early-stage formation of the developing EB ganglia while glial NC is required for the late-stage maintenance of ganglion morphology

The Community Land Model version 5 : description of new features, benchmarking, and impact of forcing uncertainty

The Community Land Model (CLM) is the land component of the Community Earth System Model (CESM) and is used in several global and regional modeling systems. In this paper, we introduce model developments included in CLM version 5 (CLM5), which is the default land component for CESM2. We assess an ensemble of simulations, including prescribed and prognostic vegetation state, multiple forcing data sets, and CLM4, CLM4.5, and CLM5, against a range of metrics including from the International Land Model Benchmarking (ILAMBv2) package. CLM5 includes new and updated processes and parameterizations: (1) dynamic land units, (2) updated parameterizations and structure for hydrology and snow (spatially explicit soil depth, dry surface layer, revised groundwater scheme, revised canopy interception and canopy snow processes, updated fresh snow density, simple firn model, and Model for Scale Adaptive River Transport), (3) plant hydraulics and hydraulic redistribution, (4) revised nitrogen cycling (flexible leaf stoichiometry, leaf N optimization for photosynthesis, and carbon costs for plant nitrogen uptake), (5) global crop model with six crop types and time‐evolving irrigated areas and fertilization rates, (6) updated urban building energy, (7) carbon isotopes, and (8) updated stomatal physiology. New optional features include demographically structured dynamic vegetation model (Functionally Assembled Terrestrial Ecosystem Simulator), ozone damage to plants, and fire trace gas emissions coupling to the atmosphere. Conclusive establishment of improvement or degradation of individual variables or metrics is challenged by forcing uncertainty, parametric uncertainty, and model structural complexity, but the multivariate metrics presented here suggest a general broad improvement from CLM4 to CLM5