Muscle Reflex Research Articles

Optimization of Female Head\u2013Neck Model with Active Reflexive Cervical Muscles in Low Severity Rear Impact Collisions

ViVA Open Human Body Model (HBM) is an open-source human body model that was developed to fill the gap of currently available models that lacked the average female size. In this study, the head–neck model of ViVA OpenHBM was further developed by adding active muscle controllers for the cervical muscles to represent the human neck muscle reflex system as studies have shown that cervical muscles influence head–neck kinematics during impacts. The muscle controller was calibrated by conducting optimization-based parameter identification of published-volunteer data. The effects of different calibration objectives to head–neck kinematics were analyzed and compared. In general, a model with active neck muscles improved the head–neck kinematics agreement with volunteer responses. The current study highlights the importance of including active muscle response to mimic the volunteer’s kinematics. A simple PD controller has found to be able to represent the behavior of the neck muscle reflex system. The optimum gains that defined the muscle controllers in the present study were able to be identified using optimizations. The present study provides a basis for describing an active muscle controller that can be used in future studies to investigate whiplash injuries in rear impacts

Ancestral persistence of vestibulospinal reflexes in axial muscles in humans.

Most studies addressing the role of vestibulospinal reflexes in balance maintenance have mainly focused on responses in the lower limbs, while limited attention has been paid to the output in trunk and back muscles. To address this issue, we tested whether electromyographic (EMG) responses to galvanic vestibular stimulations (GVS) were modulated similarly in back and leg muscles, in situations where the leg muscle responses to GVS are known to be attenuated. Body sway and surface EMG signals were recorded in the paraspinal and limb muscles of humans (n = 19) under three complementary conditions. During treadmill locomotion, EMG responses in the lower limbs were observed only during stance, whereas responses in trunk muscles were observed during all phases of the locomotor cycle. During upright standing, a slight head contact abolished the responses in the lower limbs, while the responses remained present in back muscles. Similarly, during parabolic flight-induced microgravity, EMG responses in lower limb muscles were suppressed but remained in axial muscles despite the abolished gravitational otolithic drive. Our results suggest a differentiated control of axial and appendicular muscles when a perturbation is detected by vestibular inputs. The persistence and low modulation of axial muscle responses suggests that a hard-wired reflex is functionally efficient to maintain posture. By contrast, the ankle responses to GVS occur only in balance tasks when proprioceptive feedback is congruent. This study using GVS in microgravity is the first to present an approach delineating feedforward vestibular control in unconstrained environment.NEW & NOTEWORTHY This study addresses the extent of conservation of trunk muscle control in humans. Results show that galvanic vestibular stimulation-evoked vestibular responses in trunk muscles remain strong in conditions where leg muscle responses are downmodulated (walking, standing, microgravity). This suggests a phylogenetically conserved blueprint of sensorimotor organization, with strongly hardwired vestibulospinal inputs to axial motoneurons and a higher degree of flexibility in the later emerging limb control system.

HYR-PB21-LA, a potential extended-release bupivacaine formulation, produces long-lasting local anesthesia in rats and guinea pigs

BackgroundEffective postoperative pain management plays a key role in enhancing recovery of patients after surgery. Bupivacaine hydrochloride is one of the most commonly local anesthetics used for the postoperative pain...

Bone-conducted vestibular and stretch reflexes in human neck muscles.

In normal humans, tapping the forehead produces a neck muscle reflex that is used clinically to test vestibular function, the cervical vestibular evoked myogenic potential (cVEMP). As stretch receptors can also be activated by skull taps, we investigated the origin of the early and late peaks of the bone-conducted cVEMP. In twelve normal participants, we differentially stimulated the vestibular and neck stretch receptors by applying vibration to the forehead (activating both vestibular and stretch receptors) and to the sternum (activating mainly stretch receptors). Patients with bilateral vestibulopathy (BVP; n = 26) and unilateral vestibular loss (uVL; n = 17) were also investigated for comparison. Comparison of peaks in normal subjects suggested that the early peaks were vestibular-dependent, while the later peaks had mixed vestibular and stretch input. The late peaks were present but small (1.1 amplitude ratio) in patients with BVP and absent VEMPs, confirming that they do not strictly depend on vestibular function, and largest in age-matched controls (1.5 amplitude ratio, p = 0.049), suggesting that there is an additional vestibular reflex at this latency (approx. 30ms). Patients with uVL had larger late peaks on the affected than the normal side (1.4 vs 1.0 amplitude ratio, p = 0.034). The results suggest that the early responses in SCM to skull vibration in humans are vestibular-dependent, while there is a late stretch reflex bilaterally and a late vestibular reflex in the contralateral muscle.

Learning New Feedforward Motor Commands Based on Feedback Responses.

Learning a new motor task modifies feedforward (i.e., voluntary) motor commands and such learning also changes the sensitivity of feedback responses (i.e., reflexes) to mechanical perturbations [1-9]. For example, after people learn to generate straight reaching movements in the presence of an external force field or learn to reduce shoulder muscle activity when generating pure elbow movements with shoulder fixation, evoked stretch reflex responses to mechanical perturbations reflect the learning expressed during self-initiated reaching. Such a transfer from feedforward motor commands to feedback responses is thought to take place because of shared neural circuits at the level of the spinal cord, brainstem, and cerebral cortex [10-13]. The presence of shared neural resources also predicts the transfer from feedback responses to feedforward motor commands. Little is known about such a transfer presumably because it is relatively hard to elicit learning in reflexes without engaging associated voluntary responses following mechanical perturbations. Here, we demonstrate such transfer by leveraging two approaches to elicit stretch reflexes while minimizing engagement of voluntary motor responses in the learning process: applying very short mechanical perturbations [14-19] and instructing participants to not respond to them [20-26]. Taken together, our work shows that transfer between feedforward and feedback control is bidirectional, furthering the notion that these processes share common neural circuits that underlie motor learning and transfer.

Modulation of soleus muscle H-reflexes and ankle muscle co-contraction with surface compliance during unipedal balancing in young and older adults

This study aimed to assess modulation of lower leg muscle reflex excitability and co-contraction during unipedal balancing on compliant surfaces in young and older adults. Twenty healthy adults (ten aged 18–30 years and ten aged 65–80 years) were recruited. Soleus muscle H-reflexes were elicited by electrical stimulation of the tibial nerve, while participants stood unipedally on a robot-controlled balance platform, simulating different levels of surface compliance. In addition, electromyographic data (EMG) of soleus (SOL), tibialis anterior (TA), and peroneus longus (PL) and full-body 3D kinematic data were collected. The mean absolute center of mass velocity was determined as a measure of balance performance. Soleus H-reflex data were analyzed in terms of the amplitude related to the M wave and the background EMG activity 100 ms prior to the stimulation. The relative duration of co-contraction was calculated for soleus and tibialis anterior, as well as for peroneus longus and tibialis anterior. Center of mass velocity was significantly higher in older adults compared to young adults (p<0.001) and increased with increasing surface compliance in both groups (p<0.001). The soleus H-reflex gain decreased with surface compliance in young adults (p= 0.003), while co-contraction increased {(p}_{mathrm{S}mathrm{O}mathrm{L},mathrm{T}mathrm{A}}=0.003 mathrm{a}mathrm{n}mathrm{d} {p}_{mathrm{P}mathrm{L},mathrm{T}mathrm{A}}<0.001). Older adults did not show such modulations, but showed overall lower H-reflex gains (p<0.001) and higher co-contraction than young adults {(p}_{mathrm{S}mathrm{O}mathrm{L},mathrm{T}mathrm{A}}<0.001 mathrm{a}mathrm{n}mathrm{d} {p}_{mathrm{P}mathrm{L},mathrm{T}mathrm{A}}=0.002). These results suggest an overall shift in balance control from the spinal level to supraspinal levels in older adults, which also occurred in young adults when balancing at more compliant surfaces.

Quantifying Altered Neural Connectivity of the Stretch Reflex in Chronic Hemiparetic Stroke.

Post-stroke flexion synergy limits arm/hand function and is also linked to hyperactive stretch reflexes or spasticity. It is implicated in the increased role of indirect motor pathways following damage to direct corticospinal projections. We hypothesized that this maladaptive neuroplasticity also affects stretch reflexes. Specifically, multi-synaptic interactions in indirect motor pathways may increase nonlinear neural connectivity and time lag between stretch and reflex muscle response. Continuous position perturbations were applied to the elbow joint when eleven participants with stroke generated two levels of shoulder abduction (SABD) torques with their paretic arm to induce synergy-related spasticity. Likewise, the perturbations were applied to eleven control subjects while performing SABD and elbow flexion levels matching the synergy torques in stroke. We quantified linear and non-linear connectivity and the corresponding time lags between perturbations and muscle activity. Enhanced nonlinear connectivity with a prolonged time lag was found in stroke as compared to controls. Non-linear connectivity and time lag also increased with the expression of the flexion synergy, as induced by greater SABD load levels, in stroke. This study provides new evidence of changes in neural connectivity and long-latency time lag in the stretch reflex response post-stroke. The results suggest the contribution of indirect motor pathways to synergy-related spasticity.

Long-latency Responses to a Mechanical Perturbation of the Index Finger Have a Spinal Component.

In an uncertain external environment, the motor system may need to respond rapidly to an unexpected stimulus. Limb displacement causes muscle stretch; the corrective response has multiple activity bursts, which are suggested to originate from different parts of the neuraxis. The earliest response is so fast, it can only be produced by spinal circuits; this is followed by slower components thought to arise from primary motor cortex (M1) and other supraspinal areas. Spinal cord (SC) contributions to the slower components are rarely considered. To address this, we recorded neural activity in M1 and the cervical SC during a visuomotor tracking task, in which 2 female macaque monkeys moved their index finger against a resisting motor to track an on-screen target. Following the behavioral trial, an increase in motor torque rapidly returned the finger to its starting position (lever velocity >200°/s). Many cells responded to this passive mechanical perturbation (M1: 148 of 211 cells, 70%; SC: 67 of 119 cells, 56%). The neural onset latency was faster for SC compared with M1 cells (21.7 ± 11.2 ms vs 25.5 ± 10.7 ms, respectively, mean ± SD). Using spike-triggered averaging, some cells in both regions were identified as likely premotor cells, with monosynaptic connections to motoneurons. Response latencies for these cells were compatible with a contribution to the muscle responses following the perturbation. Comparable fractions of responding neurons in both areas were active up to 100 ms after the perturbation, suggesting that both SC circuits and supraspinal centers could contribute to later response components.SIGNIFICANCE STATEMENT Following a limb perturbation, multiple reflexes help to restore limb position. Given conduction delays, the earliest part of these reflexes can only arise from spinal circuits. By contrast, long-latency reflex components are typically assumed to originate from supraspinal centers. We recorded from both spinal and motor cortical cells in monkeys responding to index finger perturbations. Many spinal interneurons, including those identified as projecting to motoneurons, responded to the perturbation; the timing of responses was compatible with a contribution to both short- and long-latency reflexes. We conclude that spinal circuits also contribute to long-latency reflexes in distal and forearm muscles, alongside supraspinal regions, such as the motor cortex and brainstem.

Combined influence of inspiratory loading and locomotor subsystolic cuff inflation on cardiovascular responses during submaximal exercise.

It is unknown if simultaneous stimulation of the respiratory and locomotor muscle afferents via inspiratory loading (IL) and locomotor subsystolic cuff inflation (CUFF) influences the cardiovascular responses during exercise. We hypothesized that combined IL and CUFF (IL + CUFF) will result in greater increases in blood pressure (MAP) and systemic vascular resistance (SVR) than IL and CUFF alone during exercise. Eight adults (6 males/2 females) were enrolled and performed four 10-min bouts of constant-load cycling eliciting 40% maximal oxygen uptake on a single day. For each exercise bout, the first 5 min consisted of spontaneous breathing. The second 5 min consisted of voluntary hyperventilation (i.e., breathing frequency of 40 breaths/min) with IL (30% maximum inspiratory pressure), CUFF (80 mmHg), IL + CUFF, or no intervention (CTL) in randomized order. During exercise, cardiac output and MAP were determined via open-circuit acetylene wash-in and manual sphygmomanometry, respectively, and SVR was calculated. Across CTL, IL, CUFF, and IL + CUFF, MAP was greater with each condition (CTL: 97 ± 14; IL: 106 ± 13; CUFF: 114 ± 14; IL + CUFF: 119 ± 15 mmHg, all P < 0.02). Furthermore, SVR was greater with IL + CUFF compared with IL, CUFF, and CTL (CTL: 6.6 ± 1.1; IL: 7.5 ± 1.4; CUFF: 7.5 ± 1.3; IL + CUFF: 8.2 ± 1.4 mmHg·L-1·min-1, all P < 0.02). Cardiac output was not different across conditions (CTL: 15.2 ± 3.8; IL: 14.8 ± 3.7; CUFF: 15.6 ± 3.5; IL + CUFF: 14.7 ± 4.3 L/min, all P > 0.05). These data demonstrate that simultaneous stimulation of respiratory and locomotor muscle afferent feedback results in additive MAP and SVR responses than IL and CUFF alone during submaximal exercise. These findings have important clinical implications for populations with exaggerated locomotor and respiratory muscle reflex feedbacks.NEW & NOTEWORTHY Reflexes arising from the respiratory and locomotor muscles influence cardiovascular regulation during exercise. However, it is unclear how the respiratory and locomotor muscle reflexes interact when simultaneously stimulated. Herein, we demonstrate that stimulation of the respiratory and locomotor muscle reflexes yielded additive cardiovascular responses during submaximal exercise.

Cerebellar Transcranial Magnetic Stimulation Disrupts Vestibular Reflexes in Standing Balance

Despite its seemingly effortless execution, standing balance is a complex task maintained by the integration of sensory feedback from visual, somatosensory (muscle, skin, joint receptors), and vestibular (inner ear) systems. The vestibular system provides feedback about head acceleration and can be manipulated experimentally by passing an electrical current percutaneously through the mastoid processes. The cerebellum plays an important role in standing balance by integrating sensory feedback to refine activity in postural muscles. A recent study has shown that experimentally depressing cerebellar activity with repetitive transcranial magnetic stimulation can influence postural sway and muscle reflex responses following electrical vestibular stimulation. The aim of this study was to investigate the impact of acute cerebellar stimulation on vestibular muscle reflex responses in different head positions during standing balance. We applied a novel combination of stochastic electrical vestibular stimulation (SVS, ±2.5 mA, 0–20 Hz) and single‐pulse cerebellum transcranial magnetic stimulation (TMS, 60% maximum stimulator output) on fifteen healthy adults (6 males, 9 females; 21–32 years old) in two head positions: head forward and head right. Muscle reflexes were recorded bilaterally with surface electromyography (EMG) from lower leg (soleus and medial gastrocnemius) and neck (sternocleidomastoid) muscles. Time‐based cumulant density and frequency‐based coherence analyses were used to evaluate the relationship between the SVS and evoked EMG responses one second before (Pre) and one second after (Post) cerebellar TMS. 50 TMS pulses were delivered per head position. Preliminary analysis performed on left medial gastrocnemius (LMG) head right data indicated a significant reduction in the short latency (SL, P = 0.0377) and medium latency (ML, P &lt; 0.0001) reflexes following cerebellar TMS (Fig. 1). In addition, a significant drop in the coherence between the SVS and LMG Pre to Post was found using a difference of coherence test. These findings support the cerebellum to be an important center for the integration of vestibular feedback for the control of standing balance.Support or Funding InformationMount Royal University Faculty of Science and TechnologyFigure 1

Differential neural coordination of bilateral hand and finger movements.

Cooperative hand movements (e.g., opening a bottle) require a close coordination of the hands. This is reflected in a neural coupling between the two sides. The aim of this study was to investigate in how far neural coupling is present not only during bilateral hand but also during bilateral finger movements. For this purpose unilateral mechanical and electrical nerve stimuli were delivered during bilateral sequentially and synchronously performed finger movements on a keyboard and, for comparison, during bilateral hand flexion movements. Electromyographic (EMG) activity and reflex responses in forearm flexor and extensor muscles of both sides were recorded and analyzed. Confounding EMG activity related to hand movements during the finger task was limited by wrist fixating braces. During the hand flexion task, complex reflex responses appeared in the forearm muscles of both sides to unilateral stimulation of the ulnar nerve (mean latency 57 ms), reflecting neural coupling between the two hands. In contrast, during the bilateral finger movement task, unilateral electrical nerve or mechanical stimulation of the right index finger was followed by dominant ipsilateral reflex responses (latency 45 and 58 ms, respectively). The results indicate that in contrast to the coupled hand movements, finger movements may not be coupled but can move independently on each side. Functionally this makes sense because during most activities of daily living, a close cooperation of the hands but not of individual fingers is needed. This independence of individual finger movements may rely on strong, specific, contralateral cortico‐motoneuronal control.

Bio-inspired neuromuscular reflex based hopping controller for a segmented robotic leg

It has been shown that human-like hopping can be achieved by muscle reflex control in neuromechanical simulations. However, it is unclear if this concept is applicable and feasible for controlling a real robot. This paper presents a low-cost two-segmented robotic leg design and demonstrates the feasibility and the benefits of the bio-inspired neuromuscular reflex based control for hopping. Simulation models were developed to describe the dynamics of the real robot. Different neuromuscular reflex pathways were investigated with the simulation models. We found that stable hopping can be achieved with both positive muscle force and length feedback, and the hopping height can be controlled by modulating the muscle force feedback gains with the return maps. The force feedback neuromuscular reflex based controller is robust against body mass and ground impedance changes. Finally, we implemented the controller on the real robot to prove the feasibility of the proposed neuromuscular reflex based control idea. This paper demonstrates the neuromuscular reflex based control approach is feasible to implement and capable of achieving stable and robust hopping in a real robot. It provides a promising direction of controlling the legged robot to achieve robust dynamic motion in the future.

Skeletal Muscle Reflex-Induced Sympathetic Dysregulation and Sensitization of Muscle Afferents in Type 1 Diabetic Rats.

The blood pressure response to exercise is exaggerated in the type 1 diabetes mellitus (T1DM). An overactive exercise pressor reflex (EPR) contributes to the potentiated pressor response. However, the mechanism(s) underlying this abnormal EPR activity remains unclear. This study tested the hypothesis that the heightened blood pressure response to exercise in T1DM is mediated by EPR-induced sympathetic overactivity. Additionally, the study examined whether the single muscle afferents are sensitized by PKC (protein kinase C) activation in this disease. Sprague-Dawley rats were intraperitoneally administered either 50 mg/kg streptozotocin (T1DM) or saline (control). At 1 to 3 weeks after administration, renal sympathetic nerve activity and mean arterial pressure responses to activation of the EPR, mechanoreflex, and metaboreflex were measured in decerebrate animals. Action potential responses to mechanical and chemical stimulation were determined in group IV afferents with pPKCα (phosphorylated-PKCα) levels assessed in dorsal root ganglia. Compared with control, EPR (58±18 versus 96±33%; P<0.05), mechanoreflex (21±13 versus 51±20%; P<0.05), and metaboreflex (40±20 versus 88±39%; P<0.01) activation in T1DM rats evoked significant increases in renal sympathetic nerve activity as well as mean arterial pressure. The response of group IV afferents to mechanical (18±24 versus 61±45 spikes; P<0.01) and chemical (0.3±0.4 versus 1.6±0.8 Hz; P<0.01) stimuli were significantly greater in T1DM than control. T1DM rats showed markedly increased pPKCα levels in dorsal root ganglia compared with control. These data suggest that in T1DM, abnormally muscle reflex-evoked increases in sympathetic activity mediate exaggerations in blood pressure. Further, sensitization of muscle afferents, potentially via PKC activation, may contribute to this abnormal circulatory responsiveness.

Clinical effect of monosialotetrahexosyl ganglioside in the treatment of neonatal intracranial hemorrhage

Objective To investigate the clinical effect of monosialotetrahexosyl ganglioside in the treatment of neonatal intracranial hemorrhage. Methods From January 2016 to December 2018, 142 neonates with intracranial hemorrhage admitted to the Maternal and Child Health Hospital of Zhoushan were randomly divided into observation group (71 cases) and control group (71 cases) according to the digital table.The control group was treated with routine treatment, while the observation group was treated with ganglioside needle on the basis of the control group.Both two groups were treated for 14 days.The therapeutic effects, muscle tone recovery time, reflex recovery time and consciousness recovery time were compared.The changes of neurobehavioral assessment score (NABA score), TNF-α, IL-1β, MMP-2, TIMP-1 and NSE levels before and after treatment were compared. Results The total effective rate of the observation group (92.96%) was higher than that of the control group (77.47%) (χ2=6.762, P<0.05). The recovery time of muscle tension, reflex and consciousness in the observation group [(7.68±1.29)d, (6.83±1.20)d and (8.34±1.54)d] were shorter than those in the control group [(10.25±2.31)d, (9.17±1.86)d and (10.53±1.08)d] (t=8.185, 8.908, 9.811, all P<0.05). After treatment, the NABA score of the observation group[(40.37±0.65)points] was higher than that of the control group[(37.16±0.93)points](t=23.838, P<0.05). The serum levels of TNF-α [(26.37±4.25)pg/L], IL-1β [(16.74±3.24)ng/L], MMP-2 [(78.39±16.57)g/L], TIMP-1 [(179.32±17.65)ng/mL] and NSE [(13.52±2.19)g/L] in the observation group were lower than those in the control group [(53.21±7.39)pg/L, (28.93±5.64)ng/L, (97.42±12.63)g/L, (238.63±28)ng/mL and (21.43±2.89)μg/L] (t=26.529, 15.792, 7.696, 14.938, 18.381, all P<0.05). Conclusion Ganglioside has good therapeutic effect on neonatal intracranial hemorrhage.It can reduce the serum levels of TNF-α, IL-1β, MMP-2, TIMP-1 and NSE, and improve the neurobehavioral function of neonates. Key words: Intracranial hemorrhages; Tumor necrosis factor-alpha; Interleukin-1beta; Matrix Metalloproteinase 2; Monosialotetrahexosyl ganglioside; Infant, newborn

Spinal Circuits Mediate a Stretch Reflex Between the Upper Limbs in Humans

Inter-limb reflexes play an important role in coordinating behaviors involving different limbs. Previous studies have demonstrated that human elbow muscles express an inter-limb stretch reflex at long-latency (50–100 ms), a timing consistent with a trans-cortical linkage. Here we probe for inter-limb stretch reflexes in the shoulder muscles of human participants. Unexpected torque pulses displaced one or both shoulders while participants adopted a steady posture against background torques. The results demonstrated inter-limb stretch reflexes occurring at short-latency for both shoulder extensors and flexors; the rapid timing (36–50 ms) must involve a spinal linkage for the two arms. Inter-limb stretch reflexes were also observed at long-latency yet they were opposite to the preceding short-latency; when the short-latency stretch reflex was excitatory then the long-latency stretch reflex was inhibitory and vice versa. Comparing the responses to contralateral arm displacement to those during simultaneous displacement of both arms revealed that inhibitory inter-limb stretch reflexes are independent of within-limb stretch reflexes, but that excitatory inter-limb stretch reflexes are suppressed by within-limb stretch reflexes. Our results provide the first demonstration of short-latency inter-limb stretch reflexes in the upper limb of humans and reveal interacting spinal circuits for within-limb and inter-limb stretch reflexes.

Cross-training effect of chronic whole-body vibration exercise: a randomized controlled study

Purpose: To determine whether unilateral leg whole-body vibration (WBV) strength training induces strength gain in the untrained contralateral leg muscle. The secondary aim was to determine the potential role of spinal neurological mechanisms regarding the effect of WBV exercise on contralateral strength training.Materials and Methods: Forty-two young adult healthy volunteers were randomized into two groups: WBV exercise and Sham control. An isometric semi-squat exercise during WBV was applied regularly through 20 sessions. WBV training was applied to the right leg in the WBV group and the left leg was isolated from vibration. Sham WBV was applied to the right leg of participants in the Control group. Pre- and post-training isokinetic torque and reflex latency of both quadricepses were evaluated.Results: The increase in the strength of right (vibrated) knee extensors was 9.4 ± 10.7% in the WBV group (p = .001) and was 1.2 ± 6.6% in the Control group (p = .724). The left (non-vibrated) extensorsvibrated) knee extensors w4 ± 8.4% in the WBV group (p = .038), whereas it decreased by 1.4 ± 7.0% in the Control (p = .294). The strength gains were significant between the two groups. WBV induced the reflex response of the quadriceps muscle in the vibrated ipsilateral leg and also in the non-vibrated contralateral leg, though with a definite delay. The WBV-induced muscle reflex (WBV-IMR) latency was 22.5 ± 7.7 ms for the vibrated leg and 39.3 ± 14.6 ms for the non-vibrated leg.Conclusions: Chronic WBV training has an effect of the cross-transfer of strength to contralateral homologous muscles. The WBV-induced muscular reflex may have a role in the mechanism of cross-transfer strength.

Whole-body vibration modulates leg muscle reflex and blood perfusion among people with chronic stroke: a randomized controlled crossover trial

This study aimed to investigate the acute effect of whole-body vibration (WBV) on the reflex and non-reflex components of spastic hypertonia and intramuscular blood perfusion among individuals with chronic stroke. Thirty-six people with chronic stroke (age: 61.4 ± 6.9 years) participated in this randomized controlled cross-over study. Each participant underwent two testing conditions: static standing for 5 minutes with WBV (30 Hz, 1.5 mm) or no-vibration. We assessed the soleus H-reflex, shear modulus (ultrasound elastography) and vascular index (color power Doppler ultrasound) of the medial gastrocnemius (MG) muscle on either paretic or non-paretic side at baseline and every 1-min post-intervention up to 5 minutes. The results revealed a significant inhibition of the H/M ratio bilaterally for the WBV condition (absolute change on paretic side: 0.61 ± 0.35, p = 0.001; non-paretic side: 0.34 ± 0.23, p = 0.001), but not the control condition. The inhibition of H-reflex was sustained up to 4 minutes and 3 minutes on the paretic and non-paretic side, respectively. The vascular index of MG muscle was significantly increased only for the WBV condition [paretic: from 0.55 ± 0.07 to 1.08 ± 0.18 (p = 0.001); non-paretic: from 0.82 ± 0.09 to 1.01 ± 0.13 (p < 0.001)], which lasted for 3 minutes and 5 minutes, respectively. No significant change of the shear modulus in the MG muscle was observed, regardless of the testing condition. Based on our results, WBV had an acute effect on modulating spastic hypertonia dominated by hyperreflexia in people with chronic stroke and facilitating greater intramuscular blood perfusion. No acute effect on passive muscle stiffness was observed.

Coordination of bilateral synchronous and asynchronous hand movements

This study deals with the coordination of bilateral synchronous and asynchronous hand movements. Cooperative hand movements (e.g. opening a bottle) were shown to be coordinated by a neural coupling, reflected in the appearance of reflex responses in forearm muscles of both sides to unilateral arm nerve stimulation. The mechanical effect of this neural coupling was investigated during bilateral synchronous and asynchronous sinusoidal tracking tasks. During the synchronous tracking task, right handed corrective movements were mirrored by the left hand, suggesting a neural coupling. During the asynchronous tracking task, large non-coupled bilateral corrective hand movements dominated. The findings indicate that during synchronous hand movements an automatic coordination of bilateral hand movements occurs. In contrast, asynchronous tasks require independent hand movements. These appear to be visually guided and voluntarily controlled, leading to larger movement errors and corrections.

Enhanced somatosensory feedback modulates cutaneous reflexes in arm muscles during self-triggered or prolonged stimulation.

Somatosensory feedback plays important roles in regulating all animal movement. The effects of sensory feedback on spinally mediated neural excitability are widely studied using cutaneous electrical stimulation paradigms. Cutaneous reflex amplitudes are reduced when stimulation is self-triggered instead ofexternally triggered. Altered spinal excitability and motor output are also observed following sustained stimulation with various parameters. Our purpose was to probe for interactions between mode and duration by investigating muscle responses following enhanced cutaneous stimulation. Fifteen neurologically intact participants were recruited. Cutaneous reflexes in the extensor carpi radialis (ECR) were evoked with brief (15ms, 300Hz) or sustained (300ms, 50Hz) stimulation trains. Stimulation was applied to the superficial radial or median nerve at the wrist and triggered by: (1) a computer program (random-triggered); (2) muscle contraction (EMG-triggered); (3) the participant pressing a button themselves (button-triggered). During each condition, isometric contractions were performed with ECR muscle activity maintained at 10, 25, 35, and 50% of maximal voluntary contraction. Stronger inhibitory reflexes were found following brief superficial radial nerve stimulation was EMG-triggered suggesting that modulation of cutaneous reflex excitability is specific to the timing when sensory 'cues' are applied during muscle contraction. No difference was observed following sustained stimulation applied to the superficial radial nerve meaning that brief and sustained stimulation affect the cutaneous pathways differentially. Nerve-specific responses were found between superficial radial and median nerve stimulation, such that greater inhibition was induced by EMG-triggered sustained stimulation to the median nerve. These observations are critical in moving beyond pathway phenomenology toward targeted sensory enhancement and amplified motor output in rehabilitation and training.

Middle Ear Muscle Reflex and Word Recognition in "Normal-Hearing" Adults: Evidence for Cochlear Synaptopathy?

Permanent threshold elevation after noise exposure, ototoxic drugs, or aging is caused by loss of sensory cells; however, animal studies show that hair cell loss is often preceded by degeneration of synapses between sensory cells and auditory nerve fibers. The silencing of these neurons, especially those with high thresholds and low spontaneous rates, degrades auditory processing and may contribute to difficulties in understanding speech in noise. Although cochlear synaptopathy can be diagnosed in animals by measuring suprathreshold auditory brainstem responses, its diagnosis in humans remains a challenge. In mice, cochlear synaptopathy is also correlated with measures of middle ear muscle (MEM) reflex strength, possibly because the missing high-threshold neurons are important drivers of this reflex. The authors hypothesized that measures of the MEM reflex might be better than other assays of peripheral function in predicting difficulties hearing in difficult listening environments in human subjects. The authors recruited 165 normal-hearing healthy subjects, between 18 and 63 years of age, with no history of ear or hearing problems, no history of neurologic disorders, and unremarkable otoscopic examinations. Word recognition in quiet and in difficult listening situations was measured in four ways: using isolated words from the Northwestern University auditory test number six corpus with either (a) 0 dB signal to noise, (b) 45% time compression with reverberation, or (c) 65% time compression with reverberation, and (d) with a modified version of the QuickSIN. Audiometric thresholds were assessed at standard and extended high frequencies. Outer hair cell function was assessed by distortion product otoacoustic emissions (DPOAEs). Middle ear function and reflexes were assessed using three methods: the acoustic reflex threshold as measured clinically, wideband tympanometry as measured clinically, and a custom wideband method that uses a pair of click probes flanking an ipsilateral noise elicitor. Other aspects of peripheral auditory function were assessed by measuring click-evoked gross potentials, that is, summating potential (SP) and action potential (AP) from ear canal electrodes. After adjusting for age and sex, word recognition scores were uncorrelated with audiometric or DPOAE thresholds, at either standard or extended high frequencies. MEM reflex thresholds were significantly correlated with scores on isolated word recognition, but not with the modified version of the QuickSIN. The highest pairwise correlations were seen using the custom assay. AP measures were correlated with some of the word scores, but not as highly as seen for the MEM custom assay, and only if amplitude was measured from SP peak to AP peak, rather than baseline to AP peak. The highest pairwise correlations with word scores, on all four tests, were seen with the SP/AP ratio, followed closely by SP itself. When all predictor variables were combined in a stepwise multivariate regression, SP/AP dominated models for all four word score outcomes. MEM measures only enhanced the adjusted r values for the 45% time compression test. The only other predictors that enhanced model performance (and only for two outcome measures) were measures of interaural threshold asymmetry. Results suggest that, among normal-hearing subjects, there is a significant peripheral contribution to diminished hearing performance in difficult listening environments that is not captured by either threshold audiometry or DPOAEs. The significant univariate correlations between word scores and either SP/AP, SP, MEM reflex thresholds, or AP amplitudes (in that order) are consistent with a type of primary neural degeneration. However, interpretation is clouded by uncertainty as to the mix of pre- and postsynaptic contributions to the click-evoked SP. None of the assays presented here has the sensitivity to diagnose neural degeneration on a case-by-case basis; however, these tests may be useful in longitudinal studies to track accumulation of neural degeneration in individual subjects.