Reflex Modulation Research Articles

Psychosocial and cardiometabolic predictors of chronic pain onset in Native Americans: serial mediation analyses of 2-year prospective data from the Oklahoma Study of Native American Pain Risk.

Chronic pain results in considerable suffering, as well as significant economic and societal costs. Previous evidence suggests that Native Americans (NAs) have higher rates of chronic pain than other U.S. racial or ethnic groups, but the mechanisms contributing to this pain disparity are poorly understood. The Oklahoma Study of Native American Pain Risk was developed to address this issue and recruited healthy, pain-free NAs and non-Hispanic Whites. Cross-sectional analyses identified several measures of adversity (eg, trauma and discrimination), cognitive-affective factors (perceived stress and pain-related anxiety/catastrophizing), and cardiometabolic factors (eg, body mass index, blood pressure, and heart rate variability) that were associated with pronociceptive processes (eg, central sensitization, descending inhibition, and hyperalgesia). Every 6-months after enrollment, eligible participants (N = 277) were recontacted and assessed for the onset of chronic pain. This study examines predictors of chronic pain onset in the 222 participants (80%) who responded over the first 2 years. The results show that NAs developed chronic pain at a higher rate than non-Hispanic Whites (OR = 2.902, P < 0.05), even after controlling for age, sex, income, and education. Moreover, serial mediation models identified several potential pathways to chronic pain onset within the NA group. These paths included perceived discrimination, psychological stress, pain-related anxiety, a composite measure of cardiometabolic risk, and impaired descending inhibition of spinal nociception (assessed from conditioned pain modulation of the nociceptive flexion reflex). These results provide the first prospective evidence for a pain disparity in NAs that seems to be promoted by psychosocial, cardiometabolic, and pronociceptive mechanisms.

Neural mapping of prepulse-induced startle reflex modulation as indices of sensory information processing in healthy and clinical populations: A systematic review.

Startle reflex is modulated when a weaker sensory stimulus (“prepulse”) precedes a startling stimulus (“pulse”). Prepulse Inhibition (PPI) is the attenuation of the startle reflex (prepulse precedes pulse by 30–500 ms), whereas Prepulse Facilitation (PPF) is the enhancement of the startle reflex (prepulse precedes pulse by 500–6000 ms). Here, we critically appraise human studies using functional neuroimaging to establish brain regions associated with PPI and PPF. Of 10 studies, nine studies revealed thalamic, striatal and frontal lobe activation during PPI in healthy groups, and activation deficits in the cortico‐striato‐pallido‐thalamic circuitry in schizophrenia (three studies) and Tourette Syndrome (two studies). One study revealed a shared network for PPI and PPF in frontal regions and cerebellum, with PPF networks recruiting superior medial gyrus and cingulate cortex. The main gaps in the literature are (i) limited PPF research and whether PPI and PPF operate on separate/shared networks, (ii) no data on sex differences in neural underpinnings of PPI and PPF, and (iii) no data on neural underpinnings of PPI and PPF in other clinical disorders.

Noncommutative matrix factorizations with an application to skew exterior algebras

Theory of matrix factorizations is useful to study hypersurfaces in commutative algebra. To study noncommutative hypersurfaces, which are important objects of study in noncommutative algebraic geometry, we introduce a notion of noncommutative matrix factorization for an arbitrary nonzero non-unit element of a ring. First we show that the category of noncommutative graded matrix factorizations is invariant under the operation called twist (this result is a generalization of the result by Cassidy-Conner-Kirkman-Moore). Then we give two category equivalences involving noncommutative matrix factorizations and totally reflexive modules (this result is analogous to the famous result by Eisenbud for commutative hypersurfaces). As an application, we describe indecomposable noncommutative graded matrix factorizations over skew exterior algebras.

Stack Optimization and Testing for its Integration in a rSOC-Based Renewable Energy Storage System

This work aims at developing an innovative solution for storing renewable energies, so-called “Smart Energy Hub” (SEH) developed by Sylfen, based on reversible Solid Oxide Cell (rSOC) technology. It is able to operate either in electrolysis (SOEC) mode storing excess electricity to produce hydrogen, or when energy needs exceed local production, in SOFC (solid oxide fuel cell) mode producing electricity (and heat) from hydrogen or any other hydrogenated fuel. Particularly this paper focuses on stack development and optimization, partly performed through the REFLEX project supported by European commission funding.To achieve the project’s objectives, in terms of efficiency and increase of system power density, as well as multi-stack operation, optimizing CEA stack is necessary to upgrade a stack originally designed for SOEC research purposes, to a stack reversibly operated, but also integrated as a part of module. This paper presents results of stack optimisations and integration of cells developed within the REFLEX project.First, a reduction in cell thickness of ~20 % led to adapting the stack manufacturing process parameters. Some tests, here presented, demonstrate that the stack performances were not affected by this change.Then, significant effort was devoted to air distribution at the Single Repeat Unit (SRU) scale to minimize pressure drop, undesirable for both global system efficiency and mechanical resistance of stack sealing. At the SRU scale, air path adjustment reduced the pressure drop by a factor 2; at stack scale, the performances obtained in i-V curves demonstrated reactants distributions were unchanged.Optimized cells (so called G2) developed in the frame of REFLEX project were then integrated in a short stack (5 cells vs. 25 full size) to be compared to short stack comprising regular cells produced by Elcogen. Both stacks were tested in terms of durability over more than 1000 hours at 700°C. A first period of about 800 h of operation was conducted alternating from SOFC to SOEC mode by steps of ≈100 h. During this first part, the stack was supplied by 50/50 H2O/H2 at total flow rate of 12.0 NmL/min/cm² on fuel side and air (clean and dry) on oxygen side. Stack performances were checked at each change of operating mode through i-V curves recorded at 800, 750 and 700°C.For the reference cell, durability tests were operated galvanostatic at 0.36 A/cm² in fuel cell mode and -0.51 A/cm² in electrolysis mode. The fuel utilization (FU) was respectively 42% in SOFC, and Steam Conversion (SC) 59% in SOEC. For the optimized cell, tests were carried out at 0.35 A/cm² (FU=41%), and -0.58 A/cm² (SC=67%). A second stage of more than 250h of operation consisted to alternate daily from SOEC to SOFC by cycles of respectively 8h and 16h. Finally, degradation was evaluated and despite the increase in SOEC current density during G2 cell testing, degradation rate was very similar for both cells in SOEC as well as in SOFC mode.A full size (25-cells) stack made of G2 cells was manufactured integrating the fluidic optimizations but also manifold and an electrical insulation necessary to operate stacks serially connected electrically within the REFLEX modules produced by Sylfen. The change of scale was validated by obtaining similar i-V curves recorded for 5-cells and 25-cells stacks.REFLEX Smart Energy Hub will be operated in ENVIPARK Torino using three modules comprising of four stacks each. Stack production has to be as uniform as possible and consequently, manufacturing process has to be optimized. Dispersion in performance, that results of cell production and stack manufacturing process is checked at final stage by i-V curves recording before delivery. Uniformity in production (in terms of tightness, reactant distribution and so initial electrochemical performance) is found to be satisfactory, the dispersion of median cell stack voltage over the stack production is less than the voltage dispersion observed between the whole cells at stack level.For near future needs in rSOC system, an increase of stack power density is required to both reduce the CAPEX and increase system energy efficiency. In that frame cells produced by Elcogen has an active cell area that was extended from 100 to 196 cm² and tested at stack levels of 5 and 25 cells, respectively. Enlarged stack performances are measured via i-V curves and compared to reference 100 cm² cells stacks. As difference in median cell voltage is less than 10 mV up to a current density of -1.25 V/cm² (80% SC), this paper shows that, from a mechanical and fluidic point of view, the enlarged cell were successfully integrated in full-scale stack. Figure 1

The 2021 Carl Ludwig Lecture. Unsympathetic autonomic regulation in heart failure: patient-inspired insights.

Defined as a structural or functional cardiac abnormality accompanied by symptoms, signs, or biomarkers of altered ventricular pressures or volumes, heart failure also is a state of autonomic disequilibrium. A large body of evidence affirms that autonomic disturbances are intrinsic to heart failure; basal or stimulated sympathetic nerve firing or neural norepinephrine (NE) release more often than not exceed homeostatic need, such that an initially adaptive adrenergic or vagal reflex response becomes maladaptive. The magnitude of such maladaptation predicts prognosis. This Ludwig lecture develops two theses: the elucidation and judiciously targeted amelioration of maladaptive autonomic disturbances offers opportunities to complement contemporary guideline-based heart failure therapy, and serendipitous single-participant insights, acquired in the course of experimental protocols with entirely different intent, can generate novel insight, inform mechanisms, and launch entirely new research directions. I précis six elements of our current synthesis of the causes and consequences of maladaptive sympathetic disequilibrium in heart failure, shaped by patient-inspired epiphanies: arterial baroreceptor reflex modulation, excitation stimulated by increased cardiac filling pressure, paradoxical muscle sympathetic activation as a peripheral neurogenic constraint on exercise capacity, renal sympathetic restraint of natriuresis, coexisting sleep apnea, and augmented chemoreceptor reflex sensitivity and then conclude by envisaging translational therapeutic opportunities.

Stack Optimization and Testing for its Integration in a rSOC-Based Renewable Energy Storage System

Stacks dedicated to rSOC operation require improvements as compared to stacks dedicated to purely SOEC or SOFC mode. Starting from an electrolysis stack, improvements have been performed in the European project REFLEX, mainly to enhance reactants distribution, reduce pressure drops, integrate new cells specifically developed as part of REFLEX project, and finally integrate larger cells to reduce stack and system cost and footprint. For easier handling, mechanical connection to the system was optimized. Long-term degradation tests were performed both for reference and optimized cells within two 5-cell stacks. A full size 25-cell stack was assembled integrating optimized connections to gases lines, specific stack clamping system and internal electrical insulation required for stack integration into REFLEX modules. For prospective reason enlarged cells were produced and integrated within first a 5-cell stack, and then a 25-cell stack. Finally, stability of performance along pre-serial manufacturing process was checked for 20 stacks before their delivery for integration into REFLEX modules.

ИНТЕГРАЦИЯ ЦИФРОВЫХ И ПЕДАГОГИЧЕСКИХ ТЕХНОЛОГИЙ В ПРОЦЕССЕ ОБУЧЕНИЯ СТУДЕНТОВ СОЦИАЛЬНО-ЭКОНОМИЧЕСКИХ И ПЕДАГОГИЧЕСКИХ НАПРАВЛЕНИЙ ПОДГОТОВКИ

Тhis study examines how to integrate the benefits of role-playing, collaborative and interactive learning, and realistic case studies in a virtual environment. The article describes the experience of implementing an educational model based on the online virtual reality platform Second Life (SL), which provides students with the opportunity to participate in role-playing games, interactive learning, and social interaction in the learning process. The proposed model consists of three modules: the module for the preparation of information, joint modeling, a reflexive module that provides practical skills by participating in a 3D game. Students and teachers who participated in the testing of the model gave a positive assessment. The main goal of developing an educational model that's based on Second Life is to improve the educational process, using the advantages of role-playing games, collaborative and interactive learning, as well as realistic cases in a virtual environment. This can be achieved using three modules: an information preparation module, a joint simulation module for studying the situation, and a reflexive module. Unlike some virtual educational systems, this model is specifically designed to help students understand the causes of problems and how to solve them through data visualization and simple modeling, easy communication, flexible interaction, collaboration, and immersion in the SL environment. By integrating the three modules in the SL environment, the model will provide more opportunities for effective collaborative learning in various fields of knowledge. In the information preparation module, teachers and students use moving avatars to perform all the actions presented in the demo virtual room in SL with the support of the Semantic Wiki Template. This template provides the platform with sections of information on the studied subject. Using it, teachers can easily pass practical tasks to the student, while students can respond and present results without having any deep training in the field of information technology.

Rats with elevated genetic risk for metabolic syndrome exhibit cognitive deficiencies when young

Metabolic syndrome (MetS) is a known risk factor for cognitive decline. Using polygenic rat models selectively bred for high and low intrinsic exercise capacity and simultaneously modelling as low and high innate risk factor for MetS respectively, we have previously shown that adult animals with lower exercise capacity/higher MetS risk perform poorly in tasks requiring flexible cognition. However, it is not known whether these deficits in cognition are present already at young age. Also, it is unclear whether the high risk genome is related also to lower-level cognition, such as sensory gating measured as prepulse inhibition. In this study, young and adult (5-8 weeks and ~9 months) rats selectively bred for 36 generations as High-Capacity Runners (HCR) or Low-Capacity Runners (LCR) were tested for behavior in an open field task, modulation of startle reflex, and spatial learning in a T-maze. HCR rats were more active in the open field than LCR rats independent of age. Responses to the startle stimulus habituated to the same extent in LCR compared to HCR rats when young, but as adults, stronger habituation was seen in the HCR animals. The prepulse inhibition of startle response was equally strong in young HCR and LCR animals but the effect was shorter lasting in HCR animals. In T-maze, adult HCR animals unexpectedly showed attenuated learning, but we interpret this finding to stem from differences in motivation rather than learning ability. Overall, in the LCR rats with the risk genome for poor aerobic fitness and MetS, indications of compromised cognitive function are present already at a young age.

Prepulse inhibition vs cognitive modulation of the hand-blink reflex

The excitability of brainstem circuitries mediating defensive blinking in response to abrupt sensory inputs is continuously modulated by cortical areas, e.g., the hand-blink reflex (HBR), elicited by intense electrical median nerve stimulation, is enhanced when the stimulated hand is close to the face, with the behavioural purpose to optimize self-protection from increased threat. Here we investigated whether such cortically mediated HBR facilitation can be influenced by prepulse inhibition (PPI), which is known to occur entirely at the subcortical level. Twenty healthy volunteers underwent HBR recordings in five experimental conditions. In conditions 1 and 2, the stimulated hand was held either near (1) or far (2) from the face, respectively. In conditions 3 and 4, stimulation of the hand near the face was preceded by a peri-liminal prepulse to the index finger of the contralateral hand held either near (3) or far from the face (4). In condition 5, participants self-triggered the stimulus eliciting the HBR. We observed a reproducible HBR in 14 out of 20 participants and measured onset latency and area of the HBR in orbicularis oculi muscles bilaterally. HBR area decreased and latency increased in condition 2 relative to condition 1; HBR area decreased and latency increased markedly in condition 3, and somewhat less in condition 4, relative to conditions 1 and 2; self-stimulation (condition 5) also suppressed HBRs, but less than prepulses. These findings indicate that PPI of the HBR is more robust than the cognitive modulation exerted by top-down cortical projections. Possibly, an attentional shift to a prepulse may serve to reduce blinking in response to perturbation when it is convenient, in a given situation, not to interrupt ongoing visual processing.

Cutaneous inputs from perineal region facilitate spinal locomotor activity and modulate cutaneous reflexes from the foot in spinal cats.

It is well known that mechanically stimulating the perineal region potently facilitates hindlimb locomotion and weight support in mammals with a spinal transection (spinal mammals). However, how perineal stimulation mediates this excitatory effect is poorly understood. We evaluated the effect of mechanically stimulating (vibration or pinch) the perineal region on ipsilateral (9-14ms onset) and contralateral (14-18ms onset) short-latency cutaneous reflex responses evoked by electrically stimulating the superficial peroneal or distal tibial nerve in seven adult spinal cats where hindlimb movement was restrained. Cutaneous reflexes were evoked before, during, and after mechanical stimulation of the perineal region. We found that vibration or pinch of the perineal region effectively triggered rhythmic activity, ipsilateral and contralateral to nerve stimulation. When electrically stimulating nerves, adding perineal stimulation modulated rhythmic activity by decreasing cycle and burst durations and by increasing the amplitude of flexors and extensors. Perineal stimulation also disrupted the timing of the ipsilateral rhythm, which had been entrained by nerve stimulation. Mechanically stimulating the perineal region decreased ipsilateral and contralateral short-latency reflex responses evoked by cutaneous inputs, a phenomenon we observed in muscles crossing different joints and located in different limbs. The results suggest that the excitatory effect of perineal stimulation on locomotion and weight support is mediated by increasing the excitability of central pattern-generating circuitry and not by increasing excitatory inputs from cutaneous afferents of the foot. Our results are consistent with a state-dependent modulation of reflexes by spinal interneuronal circuits.

The Effect of Vision on Top-Down Modulation of Hand Blink Reflex

Objective: The magnitude of hand blink reflex (HBR) increases when a threatening stimulus is positioned in the peripersonal space (PPS) compared with stimulus in the extrapersonal space (EPS). We hypothesized that the reflex increase in PPS might change depending on whether the stimulus was seen. We aimed to investigate the alterations in HBR response to understand the effects of vision on cortical modulation of HBR. Methods: The HBR was recorded from 11 healthy volunteers while the hand was far away from the face (EPS), close to the face with eyes open (PPS-eyes open), and close to the face with eyes closed (PPS-eyes closed). Changes in the response magnitudes were compared between the three conditions. Results: HBR was obtained in all subjects. As expected, there was an increase in the reflex magnitude in the PPS-eyes open condition relative to EPS. In the PPS-eyes closed condition, the duration and latency were shorter and the area under the curve was significantly smaller compared with the PPS-eyes open condition. Conclusion: The enhancement of HBR in PPS is attributed to tonic top-down modulation. Our study provides evidence for the special sensory modulation of the PPS effect on HBR and may suggest cortical modulation of top-down modulation of brainstem neural circuits.

Modulation of brainstem reflexes induced by non-invasive brain stimulation: is there a future?

Modulation of brainstem reflexes induced by non-invasive brain stimulation: is there a future?

Les réflexes urétraux : revue de la littérature

The urethrosphincter complex is involved not only in maintaining urinary continence, particularly during effort, but also for the achievement of a complete and effective micturition. Indeed, the urethra is not a simple passive channel for the evacuation of urine from the bladder to the urethral meatus, since its resistive capacities and its possibilities of modulation of the micturition reflex depend on its reflex role either as a sensory afferent or as a neuro-muscular effector. It also participates in many genito-sexual and ano-rectal réflexes. This review of the literature describes the various reflexes of the urethra as a sensory stimulus or a neuromuscular effector. All articles referenced in this review were obtained from articles indexed on Pubmed-Medline, using the keywords: "urethral reflexes; "reflex bladder"; "urination reflex"; "intravaginal; vaginal"; "anorectal; sphincter"; "Storage and voiding"; "reflexes sneezing"; "cough reflex". Other articles were selected through references of the articles issued from the first research. Only articles in English and French have been selected. The articles concerned animal and human experiments. Eight hundred and sixty-four referenced articles were founded and a total of 75articles were included, describing the various reflexes mediated by the urethra acting as a sensory afferent or mechanical effector. We differentiated the known data in humans and animals. The urethra is a complex anatomical structure ensuring, through numerous reflex mechanisms, urinary continence. Urethral resistances are modulated during efforts and depends on the bladder capacity and the intensity of the efforts. During micturition, the coordination between the bladder and the urethra is mediated by reflex pathways organized at the cerebral, spinal and lumbosacral levels. The modulation of the micturition in term of efficacy and velocity, is due in part, to the re-afferentation of the spinal reflex by continuous stimulus of the urethral canal. Many of these reflexes are imperfectly described. Finally, the urethra is implicated in reflex loops of anal continence and sexual functions.

Differential dopamine modulation of spinal reflex amplitudes is associated with the presence or absence of the autonomic nervous system

The spinal cord contains a highly collateralized network of descending dopamine (DA) fibers that stem from the dorso-posterior hypothalamic A11 region in the brain, however, the modulatory actions of DA have generally only been assessed in lumbar segments L2-L5. In contrast to these exclusively sensorimotor segments, spinal cords segments T1-L2 and, in mouse, L6-S2, additionally contain the intermediolateral (IML) nucleus, the origin of autonomic nervous system (ANS).Here, we tested if the different spinal circuits in sensorimotor and IML-containing segments react differently to the modulation of the monosynaptic reflex (MSR) by DA. Bath-application of DA (1 μM) led to a decrease of MSR amplitude in L3-L5 segments; however, in IML-containing segments (T10-L2, and S1/2) the MSR response was facilitated. We did not observe any difference in the response between thoracic (sympathetic) and lumbosacral (parasympathetic) segments. Application of the D2-receptor agonists bromocriptine or quinpirole mimicked the effects of DA, while blocking D2 receptor pathways with raclopride or application with the D1-receptor agonist SKF 38393 led to an increase of the MSR in L3-L5 segments and a decrease of the MSR in IML-containing segments. In contrast, in the presence of the gap-junction blockers, carbenoloxone and quinine, DA modulatory actions in IML-containing segments were similar to those of sensorimotor L3-L5 segments.We suggest that DA modulates MSR amplitudes in the spinal cord in a segment-specific manner, and that the differential outcome observed in ANS segments may be a result of gap junctions in the IML.

Changes in the input-output relation of the Hoffmann reflex recruitment curve after submaximal fatiguing contraction of the antagonist muscles

Purpose The central nervous system adapts strategies to compensate the decreased motor capacities of a fatigued muscle. However, data on neurophysiological adaptations of muscles other than those under fatigue are scarce. The present study was designed to evaluate the effects of submaximal fatiguing contraction (leading to a task failure) induced in ankle dorsiflexors muscles on the excitability of the Hoffmann reflex (H-reflex) of an ankle plantarflexor (soleus muscle). Materials and methods Twenty-three physically active males (75.5 ± 8.3 kg; 1.77 ± 0.08 m; 27.0 ± 8.0 years) were asked to maintain the contraction level of the right ankle dorsiflexors at 60% of the maximal isometric voluntary contraction (MIVC). Task failure was defined when the force level dropped below 40% MIVC for 5 consecutive seconds. The input-output relation of the ascending limb of the recruitment curve of the soleus H-reflex was examined at 0 min, 5 min, 10 min, 15 min and 20 min after the task failure. Results The amplitude parameter representing the first recruited motoneurons (threshold H-reflex – H@th) was significantly higher at 5 min, 10 min, 15 min and 20 min after task failure as compared to control (Hth) (p < 0.05). On the other hand, the parameter that represents the activation of the relatively higher threshold motoneurons (H@100) was reduced (as compared to control – H100), but only at 20 min after the task failure (p < 0.05). Conclusions These results suggest differential reflex modulation of the soleus H-reflex after fatigue of the ankle dorsiflexors, that probably reflects neuronal adaptations underlying motor control around the ankle joint.

Arm cycling increases the short-latency reflex from ankle dorsiflexor afferents to knee extensor muscles.

Low-intensity electrical stimulation of the common peroneal nerve (CPN) evokes a short latency reflex in the heteronymous knee extensor muscles (referred to as the CPN reflex). The CPN reflex is facilitated at a heel strike during walking, contributing to body weight support. However, the origin of the CPN reflex increase during walking remains unclear. We speculate that this increase originates from multiple sources due to a body of evidence suggesting the presence of neural coupling between the arms and legs. Therefore, we investigated the extent to which the CPN reflex is modulated during rhythmic arm cycling. Twenty-eight subjects sat in an armchair and were asked to perform arm cycling at a moderate cadence using a stationary ergometer while performing isometric contraction of the knee extensors, such that the CPN reflex was evoked. The CPN reflex was evoked by stimulating the CPN [0.9-2.0× the motor threshold (MT) in the tibialis anterior muscle] at the level of the neck of the fibula. The CPN-reflex amplitude was measured from the vastus lateralis (VL). The biphasic reflex response in the VL was evoked within 27-45 ms following CPN stimulation. The amplitude of the CPN reflex increased during arm cycling compared with that before cycling. The modulation of the CPN reflex during arm cycling was detected only for CPN stimulation intensity around 1.2× MT. Furthermore, CPN-reflex modulation was not observed during the isometric contraction of the arm or passive arm cycling. Our results suggest the presence of neural coupling between the CPN-reflex pathways and neural systems generating locomotive arm movement.NEW & NOTEWORTHY Whether locomotive arm movements contribute to the control of the reflex pathway from ankle dorsiflexor afferents to knee extensor muscles [common peroneal nerve (CPN)-reflex] is an unresolved issue. The CPN reflex in the stationary leg was facilitated only by arm cycling, and not by passive or isometric motor tasks. Our results suggest that the arm locomotor system modulates the reflex pathway from ankle dorsiflexor afferents to the knee extensor muscles.

Rectus femoris hyperreflexia contributes to Stiff-Knee gait after stroke

BackgroundStiff-Knee gait (SKG) after stroke is often accompanied by decreased knee flexion angle during the swing phase. The decreased knee flexion has been hypothesized to originate from excessive quadriceps activation. However, it is unclear whether hyperreflexia plays a role in this activation. The goal of this study was to establish the relationship between quadriceps hyperreflexia and knee flexion angle during walking in post-stroke SKG.MethodsThe rectus femoris (RF) H-reflex was recorded in 10 participants with post-stroke SKG and 10 healthy controls during standing and walking at the pre-swing phase. In order to attribute the pathological neuromodulation to quadriceps muscle hyperreflexia and activation, healthy individuals voluntarily increased quadriceps activity using electromyographic (EMG) feedback during standing and pre-swing upon RF H-reflex elicitation.ResultsWe observed a negative correlation (R = − 0.92, p = 0.001) between knee flexion angle and RF H-reflex amplitude in post-stroke SKG. In contrast, H-reflex amplitude in healthy individuals in presence (R = 0.47, p = 0.23) or absence (R = − 0.17, p = 0.46) of increased RF muscle activity was not correlated with knee flexion angle. We observed a body position-dependent RF H-reflex modulation between standing and walking in healthy individuals with voluntarily increased RF activity (d = 2.86, p = 0.007), but such modulation was absent post-stroke (d = 0.73, p = 0.296).ConclusionsRF reflex modulation is impaired in post-stroke SKG. The strong correlation between RF hyperreflexia and knee flexion angle indicates a possible regulatory role of spinal reflex excitability in post-stroke SKG. Interventions targeting quadriceps hyperreflexia could help elucidate the causal role of hyperreflexia on knee joint function in post-stroke SKG.

Simple reflexive modules over finite-dimensional algebras

Let [Formula: see text] be a finite-dimensional algebra. If [Formula: see text] is self-injective, then all modules are reflexive. Marczinzik recently has asked whether [Formula: see text] has to be self-injective in case all the simple modules are reflexive. Here, we exhibit an 8-dimensional algebra which is not self-injective, but such that all simple modules are reflexive (actually, for this example, the simple modules are the only non-projective indecomposable modules which are reflexive). In addition, we present some properties of simple reflexive modules in general. Marczinzik had motivated his question by providing large classes [Formula: see text] of algebras such that any algebra in [Formula: see text] which is not self-injective has simple modules which are not reflexive. However, as it turns out, most of these classes have the property that any algebra in [Formula: see text] which is not self-injective has simple modules which are not even torsionless.

Interactions Between Different Age-Related Factors Affecting Balance Control in Walking.

Maintaining balance during walking is a continuous sensorimotor control problem. Throughout the movement, the central nervous system has to collect sensory data about the current state of the body in space, use this information to detect possible threats to balance and adapt the movement pattern to ensure stability. Failure of this sensorimotor loop can lead to dire consequences in the form of falls, injury and death. Such failures tend to become more prevalent as people get older. While research has established a number of factors associated with higher risk of falls, we know relatively little about age-related changes of the underlying sensorimotor control loop and how such changes are related to empirically established risk factors. This paper approaches the problem of age-related fall risk from a neural control perspective. We begin by summarizing recent empirical findings about the neural control laws mapping sensory input to motor output for balance control during walking. These findings were established in young, neurotypical study populations and establish a baseline of sensorimotor control of balance. We then review correlates for deteriorating balance control in older adults, of muscle weakness, slow walking, cognitive decline, and increased visual dependency. While empirical associations between these factors and fall risk have been established reasonably well, we know relatively little about the underlying causal relationships. Establishing such causal relationships is hard, because the different factors all co-vary with age and are difficult to isolate empirically. One option to analyze the role of an individual factor for balance control is to use computational models of walking comprising all levels of the sensorimotor control loop. We introduce one such model that generates walking movement patterns from a short list of spinal reflex modules with limited supraspinal modulation for balance. We show how this model can be used to simulate empirical studies, and how comparison between the model and empirical results can indicate gaps in our current understanding of balance control. We also show how different aspects of aging can be added to this model to study their effect on balance control in isolation.

Modulation of cutaneous reflexes during sidestepping in adult humans.

A common neural control mechanism coordinates various types of rhythmic locomotion performed in the sagittal plane, but it is unclear whether frontal plane movements show similar neural patterning in adult humans. The purpose of this study was to compare cutaneous reflex modulation patterns evoked during sagittal and frontal plane rhythmic movements. Eight healthy, neurologically intact adults (three males, five females) walked and sidestepped on a treadmill at approximately 1Hz. The sural nerve of the dominant (and lead) limb was stimulated randomly every 3-7 steps at eight phases of each gait cycle. Ipsilateral electromyographic recordings from four lower leg muscles and kinematic data from the ankle were collected continuously throughout both tasks. Data from unstimulated gait cycles were used as control trials to calculate middle-latency reflex responses (80-120ms) and kinematic changes (140-220ms) following electrical stimulation. Results show that the cutaneous reflex modulation patterns were similar across both tasks despite significant differences in background EMG activity. However, increased reflex amplitudes were observed during the late swing and early stance phases of sidestepping, which directly altered ankle kinematics. These results suggest that the neural control mechanisms responsible for coordinating sagittal locomotion are flexibly modified to coordinate frontal plane activities even with very different foot landing mechanics.