-
Journal of Neurophysiology Sep 2020Although coordinated and simultaneous movement of upper and lower limb muscles is required for activities of daily living, interlimb neural interaction mechanisms and...
Although coordinated and simultaneous movement of upper and lower limb muscles is required for activities of daily living, interlimb neural interaction mechanisms and their nature are yet to be fully elucidated. The purpose of this study was to investigate effects of motor preparation and execution of ipsilateral, contralateral, and bilateral upper limb muscle contractions on the excitability of corticospinal and spinal reflex circuits of the lower limb muscles. Fourteen able-bodied individuals were recruited in each study. Experiments were conducted to investigate ) corticospinal excitability with transcranial magnetic stimulation applied on the primary motor cortex to evoke motor evoked potentials (MEPs) and ) spinal reflex excitability with transcutaneous spinal cord stimulation applied at the lumbothoracic level to evoke spinal reflexes. Measurements were recorded from multiple right lower limb muscles simultaneously during ) ipsilateral (right), ) contralateral (left), and ) bilateral (right and left) elbow flexion. The results indicate that MEPs in lower limb muscles were facilitated during both preparation and execution of elbow flexion, whereas spinal reflexes were facilitated only during motor execution. Moreover, the extent of facilitation did not differ between right, left, and bilateral contractions. In conclusion, motor preparation for upper limb muscle contractions did not affect spinal circuits but seemed to affect the supraspinal networks controlling lower limb muscles. However, actual contraction (motor execution) of upper limb muscles is required to facilitate spinal reflex circuits controlling the lower limb muscles. Moreover, interlimb remote facilitation in corticospinal and spinal reflex circuits did not depend on whether contralateral or ipsilateral hands were contracted or if they were contracted bilaterally. We found that upper limb muscle contractions facilitated corticospinal circuits controlling lower limb muscles even during motor preparation, whereas motor execution of the task was required to facilitate spinal circuits. We also found that facilitation did not depend on whether contralateral or ipsilateral hands were contracted or if they were contracted bilaterally. Overall, these findings suggest that training of unaffected upper limbs may be useful to enhance facilitation of affected lower limbs in paraplegic individuals.
Topics: Adult; Elbow; Evoked Potentials, Motor; Humans; Isometric Contraction; Lower Extremity; Motor Activity; Motor Cortex; Muscle, Skeletal; Pyramidal Tracts; Reflex; Spinal Cord; Spinal Cord Stimulation; Transcranial Magnetic Stimulation; Upper Extremity; Young Adult
PubMed: 32697605
DOI: 10.1152/jn.00705.2019 -
The Journal of Physiology Jun 2020Although the exercise pressor reflex (EPR) and the chemoreflex (CR) are recognized for their sympathoexcitatory effect, the cardiovascular implication of their...
KEY POINTS
Although the exercise pressor reflex (EPR) and the chemoreflex (CR) are recognized for their sympathoexcitatory effect, the cardiovascular implication of their interaction remains elusive. We quantified the individual and interactive cardiovascular consequences of these reflexes during exercise and revealed various modes of interaction. The EPR and hypoxia-induced CR interaction is hyper-additive for blood pressure and heart rate (responses during co-activation of the two reflexes are greater than the summation of the responses evoked by each reflex) and hypo-additive for peripheral haemodynamics (responses during co-activation of the reflexes are smaller than the summated responses). The EPR and hypercapnia-induced CR interaction results in a simple addition of the individual responses to each reflex (i.e. additive interaction). Collectively, EPR:CR co-activation results in significant cardiovascular interactions with restriction in peripheral haemodynamics, resulting from the EPR:CR interaction in hypoxia, likely having the most crucial impact on the functional capacity of an exercising human.
ABSTRACT
We investigated the interactive effect of the exercise pressor reflex (EPR) and the chemoreflex (CR) on the cardiovascular response to exercise. Eleven healthy participants (5 females) completed a total of six bouts of single-leg knee-extension exercise (60% peak work rate, 4 min each) either with or without lumbar intrathecal fentanyl to attenuate group III/IV afferent feedback from lower limbs to modify the EPR, while breathing either ambient air, normocapnic hypoxia (S O ∼79%, P O ∼43 mmHg, P CO ∼33 mmHg, pH ∼7.39), or normoxic hypercapnia (S O ∼98%, P O ∼105 mmHg, P CO ∼50 mmHg, pH ∼7.26) to modify the CR. During co-activation of the EPR and the hypoxia-induced CR (O -CR), mean arterial pressure and heart rate were significantly greater, whereas leg blood flow and leg vascular conductance were significantly lower than the summation of the responses evoked by each reflex alone. During co-activation of the EPR and the hypercapnia-induced CR (CO -CR), the haemodynamic responses were not different from the summated responses to each reflex response alone (P ≥ 0.1). Therefore, while the interaction resulting from the EPR:O -CR co-activation is hyper-additive for blood pressure and heart rate, and hypo-additive for peripheral haemodynamics, the interaction resulting from the EPR:CO -CR co-activation is simply additive for all cardiovascular parameters. Thus, EPR:CR co-activation results in significant interactions between cardiovascular reflexes, with the impact differing when the CR activation is achieved by hypoxia or hypercapnia. Since the EPR:CR co-activation with hypoxia potentiates the pressor response and restricts blood flow to contracting muscles, this interaction entails the most functional impact on an exercising human.
Topics: Blood Pressure; Exercise; Female; Humans; Hypercapnia; Hypoxia; Reflex
PubMed: 32170732
DOI: 10.1113/JP279456 -
ENeuro Feb 2023Voluntary movements are prepared before they are executed. Preparatory activity has been observed across the CNS and recently documented in first-order neurons of the...
Voluntary movements are prepared before they are executed. Preparatory activity has been observed across the CNS and recently documented in first-order neurons of the human PNS (i.e., in muscle spindles). Changes seen in sensory organs suggest that independent modulation of stretch reflex gains may represent an important component of movement preparation. The aim of the current study was to further investigate the preparatory modulation of short-latency stretch reflex responses (SLRs) and long-latency stretch reflex responses (LLRs) of the dominant upper limb of human subjects. Specifically, we investigated how different target parameters (target distance and direction) affect the preparatory tuning of stretch reflex gains in the context of goal-directed reaching, and whether any such tuning depends on preparation duration and the direction of background loads. We found that target distance produced only small variations in reflex gains. In contrast, both SLR and LLR gains were strongly modulated as a function of target direction, in a manner that facilitated the upcoming voluntary movement. This goal-directed tuning of SLR and LLR gains was present or enhanced when the preparatory delay was sufficiently long (>250 ms) and the homonymous muscle was unloaded [i.e., when a background load was first applied in the direction of homonymous muscle action (assistive loading)]. The results extend further support for a relatively slow-evolving process in reach preparation that functions to modulate reflexive muscle stiffness, likely via the independent control of fusimotor neurons. Such control can augment voluntary goal-directed movement and is triggered or enhanced when the homonymous muscle is unloaded.
Topics: Humans; Reflex, Stretch; Goals; Reflex; Muscles; Movement; Muscle, Skeletal; Electromyography
PubMed: 36781230
DOI: 10.1523/ENEURO.0438-22.2023 -
Hearing Research Feb 2022The primary startle response (SR) is an innate reaction evoked by sudden and intense acoustic, tactile or visual stimuli. In rodents and humans the SR involves reflexive...
The primary startle response (SR) is an innate reaction evoked by sudden and intense acoustic, tactile or visual stimuli. In rodents and humans the SR involves reflexive contractions of the face, neck and limb muscles. The acoustic startle response (ASR) pathway consists of auditory nerve fibers (AN), cochlear root neurons (CRNs) and giant neurons of the caudal pontine reticular nucleus (PnC), which synapse on cranial and spinal motor neurons. The tactile startle response (TSR) is transmitted by primary sensory neurons to the principal sensory (Pr5) and spinal (Sp5) trigeminal nuclei. The ventral part of Pr5 projects directly to the PnC neurons. The SR requires rapid transmission of sensory information to initiate a fast motor response. Alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPAR) are necessary to transmit auditory information to the PnC neurons and elicit the SR. AMPARs containing the glutamate AMPAR subunit 4 (GluA4) have fast kinetics, which makes them ideal candidates to transmit the SR signal. This study examined the role of GluA4 within the primary SR pathway by using GluA4 knockout (GluA4-KO) mice. Deletion of GluA4 considerably decreased the amplitude and probability of successful ASR and TSR, indicating that the presence of this subunit is critical at a common station within the startle pathway. We conclude that deletion of GluA4 affects the transmission of sensory signals from acoustic and tactile pathways to the motor component of the startle reflex. Therefore, GluA4 is required for the full response and for reliable elicitation of the startle response.
Topics: Acoustic Stimulation; Acoustics; Animals; Mice; Neurons; Reflex, Startle; Synapses
PubMed: 34915397
DOI: 10.1016/j.heares.2021.108410 -
Spinal Cord Series and Cases 2020Sacral reflexes are important to allow the SCI practitioner to gain information about the state of the sacral spinal cord segments. The presence of the bulbocavernosus... (Review)
Review
Sacral reflexes are important to allow the SCI practitioner to gain information about the state of the sacral spinal cord segments. The presence of the bulbocavernosus and/or the anal wink reflex indicate an intact spinal reflex arc and reflex conal autonomic function (as part of the upper motor neuron syndrome); their absence defines a lower motor neuron syndrome. The assessment of sacral reflexes helps predict the type of bladder, bowel and sexual functions and the related therapeutic interventions. We suggest adding the sacral component of the International Standards for the Assessment of Autonomic Function after SCI (ISAFSCI) to the International Standards for the Neurologic Classification of Spinal Cord Injury (ISNCSCI) examination so there can be a detailed description of these important functions. As an alternative, the performance of sacral reflexes should be routinely required as part of the neurologic examination after SCI. Whether the sacral motor neuron system is classified as upper or lower motor neuron injury is also quite useful and as such should be present in the ISCNSCI.
Topics: Humans; Neurologic Examination; Reflex; Sacrococcygeal Region; Spinal Cord Injuries
PubMed: 31934355
DOI: 10.1038/s41394-019-0252-2 -
The Journal of Physiology Oct 2022
Topics: Humans; Inflammation; Reflex
PubMed: 36073291
DOI: 10.1113/JP283773 -
Otology & Neurotology : Official... Mar 2021To describe the site of lesion responsible for the severe, bilateral, symmetrical, selective loss of vestibular function in Cerebellar Ataxia with Neuronopathy and...
OBJECTIVE
To describe the site of lesion responsible for the severe, bilateral, symmetrical, selective loss of vestibular function in Cerebellar Ataxia with Neuronopathy and Vestibular Areflexia Syndrome (CANVAS), an adult-onset recessively-inherited ataxia, characterized by progressive imbalance due to a combination of cerebellar, somatosensory, and selective vestibular impairment with normal hearing.
METHODS
Histologic examination of five temporal bones and the brainstems from four CANVAS patients and the brainstem only from one more, each diagnosed and followed from diagnosis to death by one of the clinician authors.
RESULTS
All five temporal bones showed severe loss of vestibular ganglion cells (cell counts 3-16% of normal), and atrophy of the vestibular nerves, whereas vestibular receptor hair cells and the vestibular nuclei were preserved. In contrast, auditory receptor hair cells, the auditory ganglia (cell counts 51-100% of normal), and the auditory nerves were relatively preserved. In addition, the cranial sensory ganglia (geniculate and trigeminal), present in two temporal bones, also showed severe degeneration.
CONCLUSIONS
In CANVAS there is a severe cranial sensory ganglionopathy neuronopathy (ganglionopathy) involving the vestibular, facial, and trigeminal ganglia but sparing the auditory ganglia. These observations, when coupled with the known spinal dorsal root ganglionopathy in CANVAS, indicate a shared pathogenesis of its somatosensory and cranial nerve manifestations. This is the first published account of both the otopathology and neuropathology of CANVAS, a disease that involves the central as well as the peripheral nervous system.
Topics: Adult; Bilateral Vestibulopathy; Cerebellar Ataxia; Humans; Reflex, Abnormal; Reflex, Vestibulo-Ocular; Vestibular Diseases
PubMed: 33492056
DOI: 10.1097/MAO.0000000000002985 -
PLoS Computational Biology May 2021The central nervous system of humans and other animals modulates spinal cord activity to achieve several locomotion behaviors. Previous neuromechanical models...
The central nervous system of humans and other animals modulates spinal cord activity to achieve several locomotion behaviors. Previous neuromechanical models investigated the modulation of human gait changing selected parameters belonging to CPGs (Central Pattern Generators) feedforward oscillatory structures or to feedback reflex circuits. CPG-based models could replicate slow and fast walking by changing only the oscillation's properties. On the other hand, reflex-based models could achieve different behaviors through optimizations of large dimensional parameter spaces. However, they could not effectively identify individual key reflex parameters responsible for gait characteristics' modulation. This study investigates which reflex parameters modulate the gait characteristics through neuromechanical simulations. A recently developed reflex-based model is used to perform optimizations with different target behaviors on speed, step length, and step duration to analyze the correlation between reflex parameters and their influence on these gait characteristics. We identified nine key parameters that may affect the target speed ranging from slow to fast walking (0.48 and 1.71 m/s) as well as a large range of step lengths (0.43 and 0.88 m) and step duration (0.51, 0.98 s). The findings show that specific reflexes during stance significantly affect step length regulation, mainly given by positive force feedback of the ankle plantarflexors' group. On the other hand, stretch reflexes active during swing of iliopsoas and gluteus maximus regulate all the gait characteristics under analysis. Additionally, the results show that the hamstrings' group's stretch reflex during the landing phase is responsible for modulating the step length and step duration. Additional validation studies in simulations demonstrated that the modulation of identified reflexes is sufficient to regulate the investigated gait characteristics. Thus, this study provides an overview of possible reflexes involved in modulating speed, step length, and step duration of human gaits.
Topics: Biomechanical Phenomena; Computational Biology; Computer Simulation; Gait; Humans; Locomotion; Models, Anatomic; Models, Neurological; Muscle, Skeletal; Musculoskeletal Physiological Phenomena; Musculoskeletal System; Psychomotor Performance; Reflex, Stretch; Walking
PubMed: 34010288
DOI: 10.1371/journal.pcbi.1008594 -
International Journal of Environmental... Feb 2023The aim of the study was to determine the relationship between changes in physiological tremor after exercise and changes in the traction properties of the stretch...
The aim of the study was to determine the relationship between changes in physiological tremor after exercise and changes in the traction properties of the stretch reflex indirectly assessed using the Hoffmann reflex test. The research involved 19 young men practicing canoe sprint (age 16.4 ± 0.7 years, body mass 74.4 ± 6.7 kg, body height 182.1 ± 4.3 cm, training experience 4.8 ± 1.6 years). During resting tests, Hoffmann reflex measurements were performed from the soleus muscle, physiological tremor of the lower limb, and the blood lactate concentration was determined. Then, a graded test was carried out on the kayak/canoe ergometer. Immediately after the exercise and in the 10th and 25th minute following the exercise, Hoffmann's reflex of the soleus muscle was measured. The physiological tremor was measured at 5, 15 and 30 min after exercise. Blood lactate concentrations were determined immediately after physiological tremor. Both the parameters of Hoffmann's reflex and physiological tremor changed significantly after exercise. There were no significant interrelationships between Hoffmann reflex measurements and physiological tremor in resting and post-exercise conditions. No significant correlation was detected between changes in physiological tremor and changes in Hoffmann reflex parameters. It is to be assumed that there is no connection between a stretch reflex and a physiological tremor.
Topics: Male; Humans; Adolescent; Tremor; Electromyography; Reflex; Muscle, Skeletal; Fatigue; Essential Tremor
PubMed: 36834132
DOI: 10.3390/ijerph20043436 -
Vision Research Sep 2019Good vision requires a near stationary image if motion blur is to be avoided. All animals with good eyesight (principally the vertebrates, arthropods and cephalopod... (Comparative Study)
Comparative Study
Good vision requires a near stationary image if motion blur is to be avoided. All animals with good eyesight (principally the vertebrates, arthropods and cephalopod molluscs) have adopted a very similar strategy for achieving this: fixations in which gaze is kept still, with saccades to change gaze direction as fast as possible. In all these groups the stability of fixations is maintained by reflexes that oppose the effects of head or body movement (the vestibulo-ocular reflex in vertebrates), and that oppose drift of the image on the retina (optokinetic and optomotor reflexes). A small number of species of molluscs and arthropods have adopted a different strategy: allowing the retinas to scan across the surroundings to acquire information. The retinas in these animals are all linear structures a few receptors wide, and scan at right angles to their long dimension. The speed of scanning varies with retinal resolution, ensuring that scan speed does not produce deleterious blur.
Topics: Animals; Eye Movements; Fixation, Ocular; Humans; Nystagmus, Optokinetic; Reflex, Vestibulo-Ocular
PubMed: 31254533
DOI: 10.1016/j.visres.2019.06.004