Muscle Reflex Research Articles

Instrumented assessment of lower and upper motor neuron signs in amyotrophic lateral sclerosis using robotic manipulation: an explorative study

BackgroundAmyotrophic lateral sclerosis (ALS) is a lethal progressive neurodegenerative disease characterized by upper motor neuron (UMN) and lower motor neuron (LMN) involvement. Their varying degree of involvement results in a clinical heterogenous picture, making clinical assessments of UMN signs in patients with ALS often challenging. We therefore explored whether instrumented assessment using robotic manipulation could potentially be a valuable tool to study signs of UMN involvement.MethodsWe examined the dynamics of the wrist joint of 15 patients with ALS and 15 healthy controls using a Wristalyzer single-axis robotic manipulator and electromyography (EMG) recordings in the flexor and extensor muscles in the forearm. Multi-sinusoidal torque perturbations were applied, during which participants were asked to either relax, comply or resist. A neuromuscular model was used to study muscle viscoelasticity, e.g. stiffness (k) and viscosity (b), and reflexive properties, such as velocity, position and force feedback gains (kv, kp and kf, respectively) that dominated the responses. We further obtained clinical signs of LMN (muscle strength) and UMN (e.g. reflexes, spasticity) dysfunction, and evaluated their relation with the estimated neuromuscular model parameters.ResultsOnly force feedback gains (kf) were elevated in patients (p = 0.033) compared to controls. Higher kf, as well as the resulting reflexive torque (Tref), were both associated with more severe UMN dysfunction in the examined arm (p = 0.040 and p < 0.001). Patients with UMN symptoms in the examined arm had increased kf and Tref compared to controls (both p = 0.037). Neither of these measures was related to muscle strength, but muscle stiffness (k) was lower in weaker patients (p = 0.012). All these findings were obtained from the relaxed test. No differences were observed during the instructions comply and resist.ConclusionsThis findings are proof-of-concept that instrumented assessment using robotic manipulation is a feasible technique in ALS, which may provide quantitative, operator-independent measures relating to UMN symptoms. Elevated force feedback gains, driving larger reflexive muscle torques, appear to be particularly indicative of clinically established levels of UMN dysfunction in the examined arm.

Guillain-Barré syndrome with overlap between the finger drop variant and acute bulbar palsy: a case report

BackgroundGuillain-Barré syndrome (GBS) is a clinically heterogenous disease and encompasses several distinct clinical variants. Overlap between these variants can pose a diagnostic challenge. We report a case of finger drop variant and acute bulbar palsy overlap as an unusual manifestation of GBS.Case presentationAn 81-year-old man presented with dysarthria, dysphagia, and upper limb weakness. Neurological examination revealed impaired tongue protrusion, the finger drop sign, and diminished brachioradial and triceps muscle reflexes. Nerve conduction studies showed reduced amplitudes and decreased velocities in the median and ulnar nerves. Cerebrospinal fluid analysis revealed albuminocytological dissociation and an anti-ganglioside antibody study revealed positivity for GM1, asialo-GM1, GT1a, GD1b, and GQ1b. As GBS was suspected, we initiated intravenous immunoglobulin treatment, resulting in gradual improvement within the next 3 weeks.ConclusionTo the best of our knowledge, this is the first reported case of an overlap between the finger drop variant and acute bulbar palsy in GBS, highlighting the importance of considering GBS when patients present with a combination of atypical symptoms. Anti-ganglioside antibodies can be helpful and add diagnostic value in these complex cases.

Changes in intra- and interlimb reflexes from forelimb cutaneous afferents after staggered thoracic lateral hemisections during locomotion in cats.

In quadrupeds, such as cats, cutaneous afferents from the forepaw dorsum signal external perturbations and send inputs to spinal circuits to co-ordinate the activity in muscles of all four limbs. How these cutaneous reflex pathways from forelimb afferents are reorganized after an incomplete spinal cord injury is not clear. Using a staggered thoracic lateral hemisections paradigm, we investigated changes in intralimb and interlimb reflex pathways by electrically stimulating the left and right superficial radial nerves in seven adult cats and recording reflex responses in five forelimb and ten hindlimb muscles. After the first (right T5-T6) and second (left T10-T11) hemisections, forelimb-hindlimb co-ordination was altered and weakened. After the second hemisection, cats required balance assistance to perform quadrupedal locomotion. Short-, mid- and long-latency homonymous and crossed reflex responses in forelimb muscles and their phase modulation remained largely unaffected after staggered hemisections. The occurrence of homolateral and diagonal mid- and long-latency responses in hindlimb muscles evoked with left and right superficial radial nerve stimulation was significantly reduced at the first time point after the first hemisection, but partially recovered at the second time point with left superficial radial nerve stimulation. These responses were lost or reduced after the second hemisection. When present, all reflex responses, including homolateral and diagonal, maintained their phase-dependent modulation. Therefore, our results show a considerable loss in cutaneous reflex transmission from cervical to lumbar levels after incomplete spinal cord injury, albeit with preservation of phase modulation, probably affecting functional responses to external perturbations. KEY POINTS: Cutaneous afferent inputs co-ordinate muscle activity in the four limbs during locomotion when the forepaw dorsum contacts an obstacle. Thoracic spinal cord injury disrupts communication between spinal locomotor centres located at cervical and lumbar levels, impairing balance and limb co-ordination. We investigated cutaneous reflexes from forelimb afferents during quadrupedal locomotion by electrically stimulating the superficial radial nerve bilaterally, before and after staggered lateral thoracic hemisections in cats. We showed a loss/reduction of mid- and long-latency homolateral and diagonal reflex responses in hindlimb muscles early after the first hemisection that partially recovered with left superficial radial nerve stimulation, before being reduced after the second hemisection. Targeting cutaneous reflex pathways from forelimb afferents projecting to the four limbs could help develop therapeutic approaches aimed at restoring transmission in ascending and descending spinal pathways.

Vocalization-induced middle ear muscle reflex and auditory fovea do not contribute to the unimpaired auditory sensitivity after intense noise exposure in the CF-FM bat, Hipposideros pratti.

Behaviors and auditory physiological responses of some species of echolocating bats remain unaffected after exposure to intense noise, but information on the underlying mechanisms remains limited. Here, we studied whether the vocalization-induced middle ear muscle (MEM) contractions (MEM reflex) and auditory fovea contributed to the unimpaired auditory sensitivity of constant frequency-frequency modulation (CF-FM) bats after exposure to broad-band intense noise. The vocalizations of the CF-FM bat, Hipposideros pratti, were inhibited through anesthesia to eliminate the vocalization-induced MEM reflex. First, the anesthetized bats were exposed to intense broad-band noise, and the findings showed that the bats could still maintain their auditory sensitivities. However, auditory sensitivities were seriously impaired in CBA/Ca mice exposed to intense noise under anesthesia. This indicated that the unimpaired auditory sensitivity in H. pratti after exposure to intense noise under anesthesia was not due to anesthetization. The bats were further exposed to low-frequency band-limited noise, whose passband did not overlap with echolocation call frequencies. The results showed that the auditory responses to sound frequencies within the noise spectrum and one-half octave higher than the spectrum were also unimpaired. Taken together, the results indicate that both vocalization-induced MEM reflex and auditory fovea do not contribute to the unimpaired auditory sensitivity in H. pratti after exposure to intense noise. The possible mechanisms underlying the unimpaired auditory sensitivity after echolocating bats were exposed to intense noise are discussed.

Associations between the medial olivocochlear reflex, middle-ear muscle reflex, and sentence-in-noise recognition using steady and pulsed noise elicitors

The middle-ear muscle reflex (MEMR) and medial olivocochlear reflex (MOCR) modify peripheral auditory function, which may reduce masking and improve speech-in-noise (SIN) recognition. Previous work and our pilot data suggest that the two reflexes respond differently to static versus dynamic noise elicitors. However, little is known about how the two reflexes work in tandem to contribute to SIN recognition. We hypothesized that SIN recognition would be significantly correlated with the strength of the MEMR and with the strength of the MOCR. Additionally, we hypothesized that SIN recognition would be best when both reflexes were activated. A total of 43 healthy, normal-hearing adults met the inclusion/exclusion criteria (35 females, age range: 19–29 years). MEMR strength was assessed using wideband absorbance. MOCR strength was assessed using transient-evoked otoacoustic emissions. SIN recognition was assessed using a modified version of the QuickSIN. All measurements were made with and without two types of contralateral noise elicitors (steady and pulsed) at two levels (50 and 65 dB SPL). Steady noise was used to primarily elicit the MOCR and pulsed noise was used to elicit both reflexes. Two baseline conditions without a contralateral elicitor were also obtained. Results revealed differences in how the MEMR and MOCR responded to elicitor type and level. Contrary to hypotheses, SIN recognition was not significantly improved in the presence of any contralateral elicitors relative to the baseline conditions. Additionally, there were no significant correlations between MEMR strength and SIN recognition, or between MOCR strength and SIN recognition. MEMR and MOCR strength were significantly correlated for pulsed noise elicitors but not steady noise elicitors. Results suggest no association between SIN recognition and the MEMR or MOCR, at least as measured and analyzed in this study. SIN recognition may have been influenced by factors not accounted for in this study, such as contextual cues, warranting further study.

Reflex Responses in Muscles of the Lower Extremities Elicited by Transcutaneous Stimulation of Cauda Equina: Part 1. Methodology and Normative Data

Introduction: Transcutaneous electrical stimulation is used to stimulate the dorsal roots of the cauda equina. Multiple elicited responses recorded in the lower extremity muscles are called posterior root muscle reflexes (PRMRs). Normal PRMR values in the muscles of healthy lower extremities have yet to be determined. Methods: Thirty subjects without known lumbosacral spinal root illness were included in this study. Subsequently, they were subjected to transcutaneous electrical stimulation of the cauda equina. Posterior root muscle reflex was recorded in the four muscle groups of both lower extremities. We elicited multiple PRMR and examined their characteristics in order to establish normal electrophysiological parameter values. Results: Posterior root muscle reflex was successfully elicited in the tibialis anterior (96.7%), gastrocnemius (100%), quadriceps femoris (93.3%), and hamstring (96.7%). No statistically significant differences were found in the intensity of stimulation, latencies, or area under the PRMR between the right and left leg muscles. The area under PRMR varied significantly among the participants. Higher body weight and abdominal girth showed a significant positive correlation with stimulation intensity for eliciting PRMR, and a significant negative correlation with the area under PRMR. Older age showed a significant negative correlation with the success of eliciting PRMR and the area under the PRMR. Conclusions: Posterior root muscle reflex is a noninvasive and successful method for eliciting selective reflex responses of cauda equina posterior roots. Obtained values could be used in future studies to evaluate the utility of this methodology in clinical practice. This methodology could improve testing of the proximal lumbosacral nervous system functional integrity.

Forelimb movements contribute to hindlimb cutaneous reflexes during locomotion in cats.

During quadrupedal locomotion, interactions between spinal and supraspinal circuits and somatosensory feedback coordinate forelimb and hindlimb movements. How this is achieved is not clear. To determine whether forelimb movements modulate hindlimb cutaneous reflexes involved in responding to an external perturbation, we stimulated the superficial peroneal nerve in six intact cats during quadrupedal locomotion and during hindlimb-only locomotion (with forelimbs standing on stationary platform) and in two cats with a low spinal transection (T12-T13) during hindlimb-only locomotion. We compared cutaneous reflexes evoked in six ipsilateral and four contralateral hindlimb muscles. Results showed similar occurrence and phase-dependent modulation of short-latency inhibitory and excitatory responses during quadrupedal and hindlimb-only locomotion in intact cats. However, the depth of modulation was reduced in the ipsilateral semitendinosus during hindlimb-only locomotion. Additionally, longer-latency responses occurred less frequently in extensor muscles bilaterally during hindlimb-only locomotion, whereas short-latency inhibitory and longer-latency excitatory responses occurred more frequently in the ipsilateral and contralateral sartorius anterior, respectively. After spinal transection, short-latency inhibitory and excitatory responses were similar to both intact conditions, whereas mid- or longer-latency excitatory responses were reduced or abolished. Our results in intact cats and the comparison with spinal-transected cats suggest that the absence of forelimb movements suppresses inputs from supraspinal structures and/or cervical cord that normally contribute to longer-latency reflex responses in hindlimb extensor muscles.NEW & NOTEWORTHY During quadrupedal locomotion, the coordination of forelimb and hindlimb movements involves central circuits and somatosensory feedback. To demonstrate how forelimb movement affects hindlimb cutaneous reflexes during locomotion, we stimulated the superficial peroneal nerve in intact cats during quadrupedal and hindlimb-only locomotion as well as in spinal-transected cats during hindlimb-only locomotion. We show that forelimb movement influences the modulation of hindlimb cutaneous reflexes, particularly the occurrence of long-latency reflex responses.

Effect of physical rehabilitation using oromotor stimulation, manual airway clearance technique, positioning, tactile and kinaesthetic stimulation (PROMPT) protocol on respiratory and neuromuscular function in neonatal respiratory distress syndrome (NRDS)- a protocol for randomized controlled trial

Background Neonatal Respiratory Distress Syndrome (NRDS) remains a significant challenge in neonatal care, often leading to respiratory compromise and neuromuscular dysfunction. While advances in medical management have improved outcomes, adjunctive therapies such as physical rehabilitation offer potential benefits yet require further investigation. This protocol outlines a randomized controlled trial aiming to evaluate the effect of Physical Rehabilitation using Oro Motor Stimulation, Manual Airway Clearance Technique, Positioning, Tactile, and Kinesthetic Stimulation (PROMPT) protocol on respiratory and neuromuscular function in neonates with NRDS. Methods The trial will include 38 neonates diagnosed with NRDS, randomly allocated into two groups: the intervention group receiving the PROMPT protocol alongside standard care, and the control group receiving standard care alone. The PROMPT protocol comprises a comprehensive approach targeting oromotor stimulation, manual airway clearance technique, optimal positioning, and tactile/kinesthetic stimulation. Outcome measures Primary outcomes will focus on respiratory parameters such as oxygenation index, ventilatory support requirements, and neuromuscular function assessed through muscle tone and reflexes. Secondary outcomes will encompass length of hospital stay, incidence of complications, and neurodevelopmental outcomes at follow-up. Results Data analysis will employ appropriate statistical methods to compare outcomes between the intervention and control groups, with adjustments for potential confounders. Ethical approval has been obtained, and informed consent will be obtained from parents or legal guardians before enrolment. Conclusion This trial protocol aims to provide valuable insights into the efficacy and safety of the PROMPT protocol as a rehabilitative intervention for NRDS. The findings may inform future clinical practice and contribute to optimizing care strategies for neonates with NRDS, ultimately improving their short- and long-term outcomes. Registration CTRI/2024/03/064911

Auditory Effects of Acoustic Noise From 3-T Brain MRI in Neonates With Hearing Protection.

Neonates with immature auditory function (eg, weak/absent middle ear muscle reflex) could conceivably be vulnerable to noise-induced hearing loss; however, it is unclear if neonates show evidence of hearing loss following MRI acoustic noise exposure. To explore the auditory effects of MRI acoustic noise in neonates. Prospective. Two independent cohorts of neonates (N = 19 and N = 18; mean gestational-age, 38.75 ± 2.18 and 39.01 ± 1.83 weeks). T1-weighted three-dimensional gradient-echo sequence, T2-weighted fast spin-echo sequence, single-shot echo-planar imaging-based diffusion-tensor imaging, single-shot echo-planar imaging-based diffusion-kurtosis imaging and T2-weighted fluid-attenuated inversion recovery sequence at 3.0 T. All neonates wore ear protection during scan protocols lasted ~40 minutes. Equivalent sound pressure levels (SPLs) were measured for both cohorts. In cohort1, left- and right-ear auditory brainstem response (ABR) was measured before (baseline) and after (follow-up) MRI, included assessment of ABR threshold, wave I, III and V latencies and interpeak interval to determine the functional status of auditory nerve and brainstem. In cohort2, baseline and follow-up left- and right-ear distortion product otoacoustic emission (DPOAE) amplitudes were assessed at 1.2 to 7.0 kHz to determine cochlear function. Wilcoxon signed-rank or paired t-tests with Bonferroni's correction were used to compare the differences between baseline and follow-up ABR and DPOAE measures. Equivalent SPLs ranged from 103.5 to 113.6 dBA. No significant differences between baseline and follow-up were detected in left- or right-ear ABR measures (P > 0.999, Bonferroni corrected) in cohort1, or in DPOAE levels at 1.2 to 7.0 kHz in cohort2 (all P > 0.999 Bonferroni corrected except for left-ear levels at 3.5 and 7.0 kHz with corrected P = 0.138 and P = 0.533). A single 40-minute 3-T MRI with equivalent SPLs of 103.5-113.6 dBA did not result in significant transient disruption of auditory function, as measured by ABR and DPOAE, in neonates with adequate hearing protection. 2. Stage 5.

Ultrasound demonstrates the three oppositely acting reflex muscle forces which close the urethra distally and at bladder neck.

Ultrasound demonstrates the three oppositely acting reflex muscle forces which close the urethra distally and at bladder neck.

Three oppositely acting reflex muscle forces close distal urethra and bladder neck

Three oppositely acting reflex muscle forces close distal urethra and bladder neck

Transperineal ultrasound demonstrates distal and bladder neck closure by 3 opposite reflex muscle forces.

Transperineal ultrasound demonstrates distal and bladder neck closure by 3 opposite reflex muscle forces.

A brief physiology and pathophysiology of the anorectum based on the Integral Theory paradigm.

The remit of this review is confined to the experimental scientific works and surgeries based on the Integral Theory paradigm. The video abstract summarizes the anorectal function, how ligaments cause dysfunction and cure of fecal incontinence and obstructed defecation by ligament repair. Anorectal function is reflex and binary, with cortical and peripheral components. The same three oppositely acting reflex muscle forces which open and close the bladder, contract against the pubourethral (PUL) and uterosacral (USL) ligaments: (I) to close the anorectum for continence when the puborectalis muscle (PRM) contracts forwards; (II) to open the anorectum prior to evacuation when the PRM relaxes; (III) to stretch the rectum in opposite directions to support the anorectal stretch receptors "N" to prevent premature activation of the defecation reflex, (fecal urgency). Weak or loose PULs or USLs may cause dysfunction of closure, of evacuation, and inability to control the defecation reflex (fecal urgency). Repair of the PUL and USL can improve or cure these dysfunctions. The perineal body (PB) acts as an anatomical support for the distal vagina, anorectum and external anal sphincter (EAS). It serves as an anchoring point for the forward action of the pubococcygeus muscle (PCM), which tensions the anterior rectal wall during closure and defecation. Bladder and bowel dysfunction have a similar pathogenesis, ligament laxity, mainly pubourethral and uterosacral, with added PB damage for anorectal dysfunction. PB damage can cause obstructive defecation and descending perineal syndrome (DPS). Repair of damaged PUL and USL can restore the closure and evacuation functions of both bladder an anorectum. DPS can be cured by repair of the PB's suspensory ligaments, deep transversus perinei.

Synergistic interaction of guanfacine or dexmedetomidine coadministered with lidocaine for cutaneous analgesia in rats

ABSTRACT Background This study examined the cutaneous analgesic effects of lidocaine co-injected with guanfacine and its comparison with dexmedetomidine. Methods Cutaneous analgesic effects are quantified through the blocking effects of the cutaneous trunci muscle reflex against skin pinpricks in rats. The dose-response curves of guanfacine, dexmedetomidine, and lidocaine were constructed and drug-drug interactions were analyzed by the ED50 isobologram. Results Subcutaneous injections of guanfacine, dexmedetomidine, and lidocaine produced dose-dependently nociceptive/sensory blockade. On the ED50 (50% effective dose) basis, the potency rankings of the drug are dexmedetomidine (0.09 [0.08–0.11] μmol/kg) > guanfacine (3.98 [2.96–5.34] μmol/kg) > lidocaine (25.40 [23.51–27.44] μmol/kg) (p < 0.01). On their equipotent doses (ED25, ED50, and ED75), the duration of sensory blockade induced by guanfacine or dexmedetomidine was longer than lidocaine’s (p < 0.01). Both guanfacine and dexmedetomidine showed synergistic effects with lidocaine. Conclusions We showed that guanfacine elicits dose-dependent cutaneous analgesia when administered subcutaneously. Lidocaine is less potent than guanfacine or dexmedetomidine. Both guanfacine and dexmedetomidine enhance the potency and duration of lidocaine. Better synergistic responses we are getting with guanfacine plus lidocaine.

Implementation of surface mechanomyography as a novel approach for objective evaluation of phasic muscle stretch reflexes in people with type 2 diabetes

IntroductionDiabetic peripheral neuropathy is the most common complication of diabetes producing metabolic disruptions in the peripheral nervous system. Alteration in the predictable nature of tendon reflexes is the most common indicator suggesting the possibility of diabetic neuropathy. Evaluation of tendon reflexes is a part of various clinical scoring systems that assess neuropathy. The conventional reflex grading scales are subjective, lack temporal data, and have high inter-rater variability. Hence, an indigenous quantification tool was developed to evaluate the tendon reflexes in order to assess diabetic peripheral neuropathy. Materials and methodsA cross-sectional study was carried out in 140 healthy volunteers and 140 patients with type 2 diabetes. The mean age of controls and diabetics (49.1 ± 8.9, 50.7 ± 7.5) years, weight (66.9 ± 9.4, 69.8 ± 11.5) kilograms and BMI (24.5 ± 3.8, 26.1 ± 4.7), respectively. All of them are subjected to evaluation of tendon reflexes using the reflex quantification tool comprised of surface mechanomyography and electrogoniometry that can provide various static and dynamic variables of tendon reflex. ResultsThe dynamic variables such as reflex amplitude, muscle velocity and angular velocity were significantly low in diabetic patients (p: <0.001) whereas latency and duration (p: <0.001) were prolonged. Furthermore, no significant difference was observed in the application of tendon striking force (p: 0.934) among the participants. ConclusionThe current study demonstrates that the proposed reflex quantification tool provides several dynamic variables of patellar tendon reflex, which are significantly affected and altered in diabetic patients suggesting the involvement of peripheral neurons.

Tongue reflex for speech posture control

Although there is no doubt from an empirical viewpoint that reflex mechanisms can contribute to tongue motor control in humans, there is limited neurophysiological evidence to support this idea. Previous results failing to observe any tonic stretch reflex in the tongue had reduced the likelihood of a reflex contribution in tongue motor control. The current study presents experimental evidence of a human tongue reflex in response to a sudden stretch while holding a posture for speech. The latency was relatively long (50 ms), which is possibly mediated through cortical-arc. The activation peak in a speech task was greater than in a non-speech task while background activation levels were similar in both tasks, and the peak amplitude in a speech task was not modulated by the additional task to react voluntarily to the perturbation. Computer simulations with a simplified linear mass-spring-damper model showed that the recorded muscle activation response is suited for the generation of tongue movement responses that were observed in a previous study with the appropriate timing when taking into account a possible physiological delay between reflex muscle activation and the corresponding force. Our results evidenced clearly that reflex mechanisms contribute to tongue posture stabilization for speech production.

Shock waves modulate corticospinal excitability: A proof of concept for further rehabilitation purposes?

Focal extracorporeal shock wave therapy (fESWT) is a physical therapy vastly studied and used for various musculoskeletal disorders. However, the effect of fESWT on central nervous system is still to be determined. To elucidate spinal and supra-spinal mechanisms of fESWT in healthy subjects, in order to widen the spectrum of its clinical applications. In this quasi-experimental, unblinded, proof-of-concept clinical study, 10 voluntary healthy subjects underwent fESWT and were assessed immediately before (T0), immediately after (T1) and seven days after (T2) the intervention. As neurophysiological outcomes, motor evoked potentials (resting motor threshold, maximal motor evoked potential and maximal compound muscle action potential ratio, cortical silent period, total conduction motor time, direct and indirect central motor conduction time), F-waves (minimal and mean latency, persistence and temporal dispersion) and H-reflex (threshold, amplitude, maximal H reflex and maximal compound muscle action potential ratio, latency) were considered. Resting motor threshold and F-waves temporal dispersion significantly decreased, respectively, from T1 and T2 and from T0 and T2 (for both, p < 0.05). H-reflex threshold increase between T0 and T1. Analysis disclosed a strong negative correlation between Δ3 cortical silent period (i.e., T2 -T1 recordings) and Δ1 Hr threshold (i.e., T1 -T0 recordings) (r = -0.66, p < 0.05), and a positive strong relationship between Δ3 cortical silent period and Δ3 Hr threshold (r = 0.63, p < 0.05). fESWT modulates corticospinal tract excitability in healthy volunteers, possibly inducing an early inhibition followed by a later facilitation after one week.

Virtual muscles and reflex control generates human-like ankle torques during gait perturbations.

A biologically-inspired actuation system, including muscles, spinal reflexes, and vestibular feedback, may be capable of achieving more natural gait mechanics in powered prostheses or exoskeletons. In this study, we developed a Virtual Muscle Reflex (VMR) system to control ankle torque and tuned it using data from human responses to anteroposterior mechanical perturbations at three walking speeds. The system consists of three Hill-Type muscles, simulated in real time, and uses feedback from ground reaction force and from stretch sensors on the virtual muscle fibers. Controller gains, muscle properties, and reflex/vestibular time delays were optimized using Covariance Matrix Adaptation (CMA) to minimize the difference between the VMR torque output and the torque measured from the experiment. We repeated the procedure using a conventional finite-state impedance controller. For both controllers, the coefficient of determination () and root-mean-square error (RMSE) was calculated as a function of time within the gait cycle. The VMR had lower RMSE than the impedance controller in 70%, and in 60% of the trials, the of the VMR controller was higher than for the impedance controller. We concluded that the VMR system can better reproduce the human responses to perturbations than the impedance controller.

Neural coordination of bilateral hand movements: evidence for an involvement of brainstem motor centres.

Bilateral hand movements are assumed to be coordinated by a neural coupling mechanism. Neural coupling is experimentally reflected in complex electromyographic (EMG) responses in the forearm muscles of both sides to unilateral electrical arm nerve stimulation (ES). The aim of this study was to examine a potential involvement of the reticulospinal system in neural coupling by the application of loud acoustic stimuli (LAS) known to activate neurons of this system. LAS, ES and combined LAS/ES were applied to healthy subjects during visually guided bilateral hand flexion-extension movements. Muscle responses to the different stimuli were evaluated by electrophysiological recordings. Unilateral electrical ulnar nerve stimulation resulted in neural coupling responses in the forearm extensors (FE) of both sides. Interestingly, LAS evoked bilateral EMG responses that were similar in their configuration to those induced by ES. The presence of startles was associated with a shift of the onset and enhanced amplitude of LAS-induced coupling-like responses. Upon combined LAS/ES application, ES facilitated ipsilateral startles and coupling-like responses. Modulation of coupling-like responses by startles, the similarity of the responses to ES and LAS, and their interaction following combined stimulation suggests that both responses are mediated by the reticulospinal system. Our findings provide novel indirect evidence that the reticulospinal system is involved in the neural coupling of hand movements. This becomes clinically relevant in subjects with a damaged corticospinal system where a dominant reticulospinal system leads to involuntary limb coupling, referred to as associated movements. KEY POINTS: Automatic coordination of hand movements is assumed to be mediated by a neural coupling mechanism reflected by bilateral reflex responses in forearm muscles to unilateral electrical arm nerve stimulation (ES). Loud acoustic stimuli (LAS) were applied to assess a potential involvement of the reticulospinal system in the neural coupling mechanism. LAS evoked a bilateral reflex response in the forearm extensors that was similar to the neural coupling response to ES, and which could be separated from the acoustic startle response. Combined application of LAS and ES resulted in a facilitation of startle and coupling-like responses ipsilateral to ES, thus indicating an interaction of afferences from both stimuli. These novel findings provide indirect evidence that the reticulospinal system is a key motor structure for the coupling of bilateral hand movements.

Identification of Neural and Non-Neural Origins of Joint Hyper-Resistance Based on a Novel Neuromechanical Model.

Joint hyper-resistance is a common symptom in neurological disorders. It has both neural and non-neural origins, but it has been challenging to distinguish different origins based on clinical tests alone. Combining instrumented tests with parameter identification based on a neuromechanical model may allow us to dissociate the different origins of joint hyper-resistance in individual patients. However, this requires that the model captures the underlying mechanisms. Here, we propose a neuromechanical model that, in contrast to previously proposed models, accounts for muscle short-range stiffness (SRS) and its interaction with muscle tone and reflex activity. We collected knee angle trajectories during the pendulum test in 15 children with cerebral palsy (CP) and 5 typically developing children. We did the test in two conditions - hold and pre-movement - that have been shown to alter knee movement. We modeled the lower leg as an inverted pendulum actuated by two antagonistic Hill-type muscles extended with SRS. Reflex activity was modeled as delayed, linear feedback from muscle force. We estimated neural and non-neural parameters by optimizing the fit between simulated and measured knee angle trajectories during the hold condition. The model could fit a wide range of knee angle trajectories in the hold condition. The model with personalized parameters predicted the effect of pre-movement demonstrating that the model captured the underlying mechanism and subject-specific deficits. Our model may help with the identification of neural and non-neural origins of joint hyper-resistance and thereby opens perspectives for improved diagnosis and treatment selection in children with spastic CP, but such applications require further studies to establish the method's reliability.