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Brain : a Journal of Neurology Sep 2023Although rigidity is a cardinal motor sign in patients with Parkinson's disease (PD), the instrumental measurement of this clinical phenomenon is largely lacking, and...
Although rigidity is a cardinal motor sign in patients with Parkinson's disease (PD), the instrumental measurement of this clinical phenomenon is largely lacking, and its pathophysiological underpinning remains still unclear. Further advances in the field would require innovative methodological approaches able to measure parkinsonian rigidity objectively, discriminate the different biomechanical sources of muscle tone (neural or visco-elastic components), and finally clarify the contribution to 'objective rigidity' exerted by neurophysiological responses, which have previously been associated with this clinical sign (i.e. the long-latency stretch-induced reflex). Twenty patients with PD (67.3 ± 6.9 years) and 25 age- and sex-matched controls (66.9 ± 7.4 years) were recruited. Rigidity was measured clinically and through a robotic device. Participants underwent robot-assisted wrist extensions at seven different angular velocities randomly applied, when ON therapy. For each value of angular velocity, several biomechanical (i.e. elastic, viscous and neural components) and neurophysiological measures (i.e. short and long-latency reflex and shortening reaction) were synchronously assessed and correlated with the clinical score of rigidity (i.e. Unified Parkinson's Disease Rating Scale-part III, subitems for the upper limb). The biomechanical investigation allowed us to measure 'objective rigidity' in PD and estimate the neuronal source of this phenomenon. In patients, 'objective rigidity' progressively increased along with the rise of angular velocities during robot-assisted wrist extensions. The neurophysiological examination disclosed increased long-latency reflexes, but not short-latency reflexes nor shortening reaction, in PD compared with control subjects. Long-latency reflexes progressively increased according to angular velocities only in patients with PD. Lastly, specific biomechanical and neurophysiological abnormalities correlated with the clinical score of rigidity. 'Objective rigidity' in PD correlates with velocity-dependent abnormal neuronal activity. The observations overall (i.e. the velocity-dependent feature of biomechanical and neurophysiological measures of objective rigidity) would point to a putative subcortical network responsible for 'objective rigidity' in PD, which requires further investigation.
Topics: Humans; Parkinson Disease; Muscle Rigidity; Reflex, Stretch; Reflex, Abnormal; Electromyography
PubMed: 37018058
DOI: 10.1093/brain/awad114 -
The Journal of Physiology Jun 2002To investigate whether the intensity and duration of a sustained contraction influences reflex regulation, we compared sustained fatiguing contractions at 25 % and 50 %...
To investigate whether the intensity and duration of a sustained contraction influences reflex regulation, we compared sustained fatiguing contractions at 25 % and 50 % of maximal voluntary contraction (MVC) force in the human abductor pollicis brevis (APB) muscle. Because the activation of motoneurones during fatigue may be reflexively controlled by the metabolic status of the muscle, we also compared reflex activities during sustained and intermittent (6 s contraction, 4 s rest) contractions at 25 % MVC for an identical duration. The short-latency Hoffmann(H) reflex and the long-latency reflex (LLR) were recorded during voluntary contractions, before, during and after the fatigue tests, with each response normalised to the compound muscle action potential (M-wave). The results showed that fatigue during sustained contractions was inversely related to the intensity, and hence the duration, of the effort. The MVC force and associated surface electromyogram (EMG) declined by 26.2 % and 35.2 %, respectively, after the sustained contraction at 50 % MVC, and by 34.2 % and 44.2 % after the sustained contraction at 25 % MVC. Although the average EMG increased progressively with time during the two sustained fatiguing contractions, the amplitudes of the H and LLR reflexes decreased significantly. Combined with previous data (Duchateau & Hainaut, 1993), the results show that the effect on the H reflex is independent of the intensity of the sustained contraction, whereas the decline in the LLR is closely related to the duration of the contraction. Because there were no changes in the intermittent test at 25 % MVC, the results indicate that the net excitatory spinal and supraspinal reflex-mediated input to the motoneurone pool is reduced. This decline in excitation to the motoneurones, however, can be temporarily compensated by an enhancement of the central drive.
Topics: Action Potentials; Adult; Electric Stimulation; Electromyography; Female; H-Reflex; Humans; Male; Middle Aged; Muscle Contraction; Muscle Fatigue; Muscle, Skeletal; Reflex
PubMed: 12068054
DOI: 10.1113/jphysiol.2002.016790 -
Neuromodulation : Journal of the... Jun 2024Low-intensity, focused ultrasound (FUS) is an emerging noninvasive neuromodulation approach, with improved spatial and temporal resolution and penetration depth compared...
OBJECTIVES
Low-intensity, focused ultrasound (FUS) is an emerging noninvasive neuromodulation approach, with improved spatial and temporal resolution and penetration depth compared to other noninvasive electrical stimulation strategies. FUS has been used to modulate circuits in the brain and the peripheral nervous system, however, its potential to modulate spinal circuits is unclear. In this study, we assessed the effect of trans-spinal FUS (tsFUS) on spinal reflexes in healthy rats.
MATERIALS AND METHODS
tsFUS targeting different spinal segments was delivered for 1 minute, under anesthesia. Monosynaptic H-reflex of the sciatic nerve, polysynaptic flexor reflex of the sural nerve, and withdrawal reflex tested with a hot plate were measured before, during, and after tsFUS.
RESULTS
tsFUS reversibly suppresses the H-reflex in a spinal segment-, acoustic pressure- and pulse-repetition frequency (PRF)-dependent manner. tsFUS with high PRF augments the degree of homosynaptic depression of the H-reflex observed with paired stimuli. It suppresses the windup of components of the flexor reflex associated with slower, C-afferent, but not faster, A- afferent fibers. Finally, it increases the latency of the withdrawal reflex. tsFUS does not elicit neuronal loss in the spinal cord.
CONCLUSIONS
Our study provides evidence that tsFUS reversibly suppresses spinal reflexes and suggests that tsFUS could be a safe and effective strategy for spinal cord neuromodulation in disorders associated with hyperreflexia, including spasticity after spinal cord injury and painful syndromes.
Topics: Animals; Rats; Rats, Sprague-Dawley; Spinal Cord; Male; H-Reflex; Reflex; Sciatic Nerve
PubMed: 37530695
DOI: 10.1016/j.neurom.2023.04.476 -
BioMed Research International 2014During dynamic exercise, mechanisms controlling the cardiovascular apparatus operate to provide adequate oxygen to fulfill metabolic demand of exercising muscles and to... (Review)
Review
During dynamic exercise, mechanisms controlling the cardiovascular apparatus operate to provide adequate oxygen to fulfill metabolic demand of exercising muscles and to guarantee metabolic end-products washout. Moreover, arterial blood pressure is regulated to maintain adequate perfusion of the vital organs without excessive pressure variations. The autonomic nervous system adjustments are characterized by a parasympathetic withdrawal and a sympathetic activation. In this review, we briefly summarize neural reflexes operating during dynamic exercise. The main focus of the present review will be on the central command, the arterial baroreflex and chemoreflex, and the exercise pressure reflex. The regulation and integration of these reflexes operating during dynamic exercise and their possible role in the pathophysiology of some cardiovascular diseases are also discussed.
Topics: Brain; Cardiovascular System; Exercise; Humans; Neurons, Afferent; Peripheral Nervous System; Reflex
PubMed: 24818143
DOI: 10.1155/2014/478965 -
Psychophysiology Mar 2011The postauricular reflex is a relatively new psychophysiological measure of appetitive emotional processing during picture viewing. However, the degree to which other...
The postauricular reflex is a relatively new psychophysiological measure of appetitive emotional processing during picture viewing. However, the degree to which other auricular (i.e., superior and anterior auricular) muscles might exhibit reflexive activity congruent with that found in the postauricular muscle has not been investigated, nor has the robustness of postauricular reflex modulation across stimulus modality. In this study, postauricular reflexes were the only reflexes that showed consistent emotional modulation across ears and genders. Additionally, postauricular reflexes were significantly modulated for both emotional pictures and sounds; in both cases, postauricular reflexes were greatest during pleasant stimuli.
Topics: Acoustic Stimulation; Data Interpretation, Statistical; Ear Auricle; Emotions; Female; Humans; Male; Noise; Photic Stimulation; Reflex; Reflex, Startle; Sex Characteristics; Young Adult
PubMed: 20636290
DOI: 10.1111/j.1469-8986.2010.01071.x -
Journal of Neurologic Physical Therapy... Jul 2021Balance disorders and dizziness are common in people with multiple sclerosis (MS), suggesting dysfunction of the vestibular system. Evaluating how people with MS perform...
BACKGROUND AND PURPOSE
Balance disorders and dizziness are common in people with multiple sclerosis (MS), suggesting dysfunction of the vestibular system. Evaluating how people with MS perform on objective clinical vestibular tools will help broaden understanding of vestibular function in MS. This cross-sectional study's goal was to complete a robust battery of vestibular-ocular reflex (VOR), dynamic visual acuity (DVA), subjective visual vertical (SVV), and cervical and ocular vestibular-evoked myogenic potential (c/oVEMP) tests in people with and without MS.
METHODS
Forty people with relapsing-remitting MS (Expanded Disability Status Scale [EDSS] ≤6.5) and 20 controls completed the vestibular testing battery. Results were compared between groups and correlations with EDSS scores were calculated.
RESULTS
People with MS were less able to visually cancel their VOR and showed a larger variance in response on SVV. EDSS significantly correlated with VOR cancellation, SVV variance, and DVA lines lost; linear regression showed that VOR cancellation and SVV variance significantly predicted EDSS.
DISCUSSION AND CONCLUSION
Vestibular functions requiring central integration of vestibular information, but not reflexive vestibular functions like VEMP, were impaired in people with MS and correlated with EDSS, suggesting that clinical evaluation of functions requiring central integration best evaluates MS-related vestibular dysfunction. Measures assessing central vestibular integration and not vestibular reflexes may be more sensitive to detecting vestibular deficits in people with mild to moderate MS.Video Abstract available for more insight from the authors (see Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A344).
Topics: Cross-Sectional Studies; Humans; Multiple Sclerosis; Reflex, Vestibulo-Ocular; Vestibular Evoked Myogenic Potentials; Vestibule, Labyrinth
PubMed: 33867456
DOI: 10.1097/NPT.0000000000000358 -
Development and Psychopathology 2009This commentary reviews and reflects on the studies of this special section: studies that collectively provide compelling evidence for meaningful changes in stress- and... (Review)
Review
This commentary reviews and reflects on the studies of this special section: studies that collectively provide compelling evidence for meaningful changes in stress- and emotionally reactive psychophysiological systems with the transition from middle childhood into adolescence. The observed changes were complex and often overlaid upon ontogenetic differences in basal levels of activation of these systems. Maturational increases in responsiveness to stressors were stressor dependent and differentially expressed across autonomic and hormonal measures. Pubertal status increased the impact of some affective valence manipulations, although not significantly influencing others, including negative affect-related potentiation of startle/reflexes. Such ontogenetic increases in stressor and affect sensitivity may have implications for developmental psychopathology. Developmental increases in stressor reactivity may normally aid youth in responding adaptively to the challenges of adolescence, but may result in stress dysregulation among at-risk adolescents, increasing further their vulnerability for psychopathology. Pubertal-related increases in sensitivity to emotionally laden stimuli may exacerbate individual predispositions for exaggerated affective processing, perhaps contributing to the emergence of psychological disorders in these youth. Together, these studies, with their innovative use of autonomic, reflexive, and hormonal measures to index age- and pubertal-related changes in reactivity to stressors and affective stimuli, provide promising directions for future research. Some of these, along with a few cautionary notes, are outlined.
Topics: Adolescent; Affect; Aging; Blinking; Child; Emotions; Humans; Puberty; Reflex, Startle; Stress, Psychological
PubMed: 19144224
DOI: 10.1017/S0954579409000066 -
International Journal of Environmental... Mar 2022Background: Primitive reflexes (PRs) are observed as an automatic response to a specific stimulus. They are vivid from intrauterine life to 6 months postnatal. The... (Observational Study)
Observational Study
Background: Primitive reflexes (PRs) are observed as an automatic response to a specific stimulus. They are vivid from intrauterine life to 6 months postnatal. The reactions are inhibited with the growing maturation of the central nervous system (CNS). In some cases, when the natural process of development is incorrect, PRs manifest later. The analysis of differentiation in gait parameters in children with persistent PRs is important for better understanding their specific behaviour and movement. This study’s aim was to investigate the influence of active PRs on the gait parameters of preschool children. Methods: There were 50 children examined, 30 girls and 20 boys. They were 3.5−6 years old. The children had persistent PRs in the trace form. Each child was examined by S. Goddard’s Battery Test. The acquisition of the spatial-temporal gait parameters was performed using a BTS G-SENSOR measurement instrument. Participants walked barefoot, in the most natural way for them, at a self-selected speed on a 5 m walkway, then turned around and went back. They performed this twice. Results: The reflex activity influences gait cycle duration (p = 0.0099), the left step length (p = 0.0002), the left double support phase (p = 0.0024), the right double support phase (p = 0.0258) and the right single phase. Difficulties in recreating the crawling pattern and GRASP reflex influence gait cadence (p < 0.05). The left GRASP reflex corresponds to step length (p < 0.05). The activeness of the symmetrical tonic neck reflex correlates with the right single support (p < 0.05). Conclusion: The presence of PRs affect walking gait in preschool children.
Topics: Child; Child, Preschool; Female; Gait; Humans; Male; Movement; Reflex; Reflex, Abnormal; Walking
PubMed: 35409750
DOI: 10.3390/ijerph19074070 -
Experimental Physiology Oct 2016What is the central question of this study? The aim was to determine whether specific reflex connections operate between intercostal afferents and the scalene muscles in...
What is the central question of this study? The aim was to determine whether specific reflex connections operate between intercostal afferents and the scalene muscles in humans, and whether these connections operate after a clinically complete cervical spinal cord injury. What is the main finding and its importance? This is the first description of a short-latency inhibitory reflex connection between intercostal afferents from intercostal spaces to the scalene muscles in able-bodied participants. We suggest that this reflex is mediated by large-diameter afferents. This intercostal-to-scalene inhibitory reflex is absent after cervical spinal cord injury and may provide a way to monitor the progress of the injury. Short-latency intersegmental reflexes have been described for various respiratory muscles in animals. In humans, however, only short-latency reflex responses to phrenic nerve stimulation have been described. Here, we examined the reflex connections between intercostal afferents and scalene muscles in humans. Surface EMG recordings were made from scalene muscles bilaterally, in seven able-bodied participants and seven participants with motor- and sensory-complete cervical spinal cord injury (median 32 years postinjury, range 5 months to 44 years). We recorded the reflex responses produced by stimulation of the eighth or tenth left intercostal nerve. A short-latency (∼38 ms) inhibitory reflex was evident in able-bodied participants, in ipsilateral and contralateral scalene muscles. This bilateral intersegmental inhibitory reflex occurred in 46% of recordings at low stimulus intensities (at three times motor threshold). It was more frequent (in 75-85% of recordings) at higher stimulus intensities (six and nine times motor threshold), but onset latency (38 ± 9 ms, mean ± SD) and the size of inhibition (23 ± 10%) did not change with stimulus intensity. The reflex was absent in all participants with spinal cord injury. As the intercostal-to-scalene reflex did not increase with larger stimulus intensities, it is likely to be mediated by large-diameter intercostal muscle afferents. This is the first demonstration of an intercostal-to-scalene reflex. As the reflex requires intact spinal connections, it may be a useful marker for recovery of thoracic or cervical spinal injury.
Topics: Adult; Female; Humans; Intercostal Muscles; Male; Middle Aged; Motor Neurons; Neurons, Afferent; Reflex; Spinal Cord Injuries
PubMed: 27460516
DOI: 10.1113/EP085907 -
Restorative Neurology and Neuroscience 2006This review summarizes possible spinal reflexes involved in micturition control as well as current treatments for lower urinary tract dysfunction after spinal cord... (Review)
Review
PURPOSE
This review summarizes possible spinal reflexes involved in micturition control as well as current treatments for lower urinary tract dysfunction after spinal cord injury (SCI) in an effort to further promote the development of new treatments for people with SCI.
METHODS
A systematic literature search was conducted on the Medline database, and on the Web of Science.
RESULTS
After SCI normal functions of the lower urinary tract are lost. The detrusor contracts frequently even at a small bladder volume, which results in urinary incontinence. In addition, the hyperactive bladder can not empty well because the urethral sphincter contracts simultaneously with the bladder (detrusor sphincter dyssynergia), which results in a large residual volume of urine. The malfunction of the lower urinary tract after SCI is caused by remaining and newly emerged bladder and urethral sphincter spinal reflexes. Current treatments have either limited success or troublesome side effects, and many new treatments are under development.
CONCLUSIONS
In order to restore the functions of the lower urinary tract after SCI, efforts should be directed at re-establishing the coordination between the spinal reflex control of bladder and urethral sphincter using either pharmacological or neurophysiological approaches.
Topics: Animals; Humans; Models, Biological; Muscle, Smooth; Reflex; Spinal Cord Injuries; Urinary Bladder; Urinary Incontinence
PubMed: 16720943
DOI: No ID Found