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Journal of Neurophysiology Mar 2023Operant conditioning of a spinal monosynaptic pathway using the Hoffman reflex (H-reflex) is well established in animal and human studies. There is a subset within the...
Operant conditioning of a spinal monosynaptic pathway using the Hoffman reflex (H-reflex) is well established in animal and human studies. There is a subset within the human population (∼20% nonresponders) who are unable to up train this pathway suggesting some distinct or unique identifying characteristics. Importantly, females, who have a nine times higher rate of injury during human performance activities than men, have been understudied in areas of CNS neuroplasticity. Our long-term goal is to understand if innate ability to rapidly up train the H-reflex is predictive of future performance-based injury among females. In this study, we primarily determined whether healthy, young females could rapidly increase the H-reflex within a single session of operant conditioning and secondarily determined if electro-physiological, humoral, cognitive, anthropometric, or anxiety biomarkers distinguished the responders from nonresponders. Eighteen females (mean age: 24) participated in the study. Overall, females showed a group main effect for up training the H-reflex ( < 0.05). Of the cohort, 10 of 18 females met the criteria for up training the H-reflex (responders). The responders showed lower levels of estradiol ( < 0.05). A multivariate stepwise regression model supported that extracellular to intracellular water ratio (ECW/ICW) and H-max/M-max ratio explained 60% of the variation in up training among females. These findings support that females can acutely upregulate the H-reflex with training and that electro-physiological and hormonal factors may be associated with the up training. Young females who acutely increase their H-reflexes with operant conditioning had lower levels of estradiol. However, the best predictors of those who could up-train the H-reflex were baseline H-reflex excitability (H-max/M-max) and extracellular to intracellular water ratio (ECW/ICW). Future studies are warranted to understand the complex relationship between operant conditioning, human performance, and injury among active young females.
Topics: Male; Animals; Humans; Female; Young Adult; Adult; H-Reflex; Conditioning, Operant; Spinal Cord Injuries; Neuronal Plasticity; Electromyography
PubMed: 36791051
DOI: 10.1152/jn.00188.2022 -
Cephalalgia : An International Journal... Jul 2023Previous findings indicate that the blink reflex is useful to distinguish between primary (classical/idiopathic) and secondary trigeminal neuralgia. No prior studies...
BACKGROUND
Previous findings indicate that the blink reflex is useful to distinguish between primary (classical/idiopathic) and secondary trigeminal neuralgia. No prior studies have investigated whether the blink reflex could identify differences in electrophysiological responses between classical and idiopathic trigeminal neuralgia. With this in mind, we investigated the blink reflex in a cohort of classical and idiopathic trigeminal neuralgia patients.
METHODS
Participants were consecutively enrolled in the study. According to magnetic resonance imaging findings, the patients were subgrouped into either classical or idiopathic trigeminal neuralgia. Assessors were blinded to the subgroup and pain side, and the blink reflex was examined to assess R1 and R2 latencies, as well as the area under the curve.
RESULTS
The study group constituted of 55 patients with primary trigeminal neuralgia: 25 patients with classical trigeminal neuralgia and 30 patients with idiopathic trigeminal neuralgia. None of the blink reflex latencies (R1 and R2) or the area under the curve significantly differed between the two subgroups when adjusted for age and sex ( > 0.05).
CONCLUSIONS
Our findings suggest that the blink reflex cannot be used to differentiate classical and idiopathic trigeminal neuralgia patients, and that both subgroups may share common pathophysiological mechanisms. ClinicalTrials.gov Identifier: NCT05328661.
Topics: Humans; Trigeminal Neuralgia; Blinking; Trigeminal Nerve; Reflex
PubMed: 37525973
DOI: 10.1177/03331024231191136 -
Experimental Brain Research Mar 2022The purpose of this study was to examine corticospinal modulation of spinal reflex excitability, by determining the effect of transcranial magnetic stimulation (TMS) on...
The purpose of this study was to examine corticospinal modulation of spinal reflex excitability, by determining the effect of transcranial magnetic stimulation (TMS) on soleus H-reflexes while they were almost completely suppressed by lower extremity vibration. In 15 healthy adults, a novel method of single-limb vibration (0.6 g, 30 Hz, 0.33 mm displacement) was applied to the non-dominant leg. Soleus muscle responses were examined in six stimulation conditions: (1) H-reflex elicited by tibial nerve stimulation, (2) tibial nerve stimulation during vibration, (3) subthreshold TMS, (4) subthreshold TMS during vibration, (5) tibial nerve stimulation 10 ms after a subthreshold TMS pulse, and (6) tibial nerve stimulation 10 ms after a subthreshold TMS pulse, during vibration. With or without vibration, subthreshold TMS produced no motor evoked potentials and had no effect on soleus electromyography (p > 0.05). In the absence of vibration, H-reflex amplitudes were not affected by subthreshold TMS conditioning (median (md) 35, interquartile range (IQ) 18-56 vs. md 46, IQ 22-59% of the maximal M wave (Mmax), p > 0.05). During vibration, however, unconditioned H-reflexes were nearly abolished, and a TMS conditioning pulse increased the H-reflex more than fourfold (md 0.3, IQ 0.1-0.7 vs. md 2, IQ 0.9-5.0% of Mmax, p < 0.008). Limb vibration alone had no significant effect on corticospinal excitability. In the absence of vibration, a subthreshold TMS pulse did not influence the soleus H-reflex. During limb vibration, however, while the H-reflex was almost completely suppressed, a subthreshold TMS pulse partially restored the H-reflex. This disinhibition of the H-reflex by a corticospinal signal may represent a mechanism involved in the control of voluntary movement. Corticospinal signals that carry the descending motor command may also reduce presynaptic inhibition, temporarily increasing the impact of sensory inputs on motoneuron activation.
Topics: Adult; Depression; Electric Stimulation; Electromyography; Evoked Potentials, Motor; H-Reflex; Humans; Muscle, Skeletal; Transcranial Magnetic Stimulation; Vibration
PubMed: 35044475
DOI: 10.1007/s00221-022-06306-w -
The Journal of Physiology May 2021In people or animals with incomplete spinal cord injury (SCI), changing a spinal reflex through an operant conditioning protocol can improve locomotion. All previous...
KEY POINTS
In people or animals with incomplete spinal cord injury (SCI), changing a spinal reflex through an operant conditioning protocol can improve locomotion. All previous studies conditioned the reflex during steady-state maintenance of a specific posture. By contrast, the present study down-conditioned the reflex during the swing-phase of locomotion in people with hyperreflexia as a result of chronic incomplete SCI. The aim was to modify the functioning of the reflex in a specific phase of a dynamic movement. This novel swing-phase conditioning protocol decreased the reflex much faster and farther than did the steady-state protocol in people or animals with or without SCI, and it also improved locomotion. The reflex decrease persisted for at least 6 months after conditioning ended. The results suggest that conditioning reflex function in a specific phase of a dynamic movement offers a new approach to enhancing and/or accelerating recovery after SCI or in other disorders.
ABSTRACT
In animals and people with incomplete spinal cord injury, appropriate operant conditioning of a spinal reflex can improve impaired locomotion. In all previous conditioning studies, the reflex was conditioned during steady-state maintenance of a stable posture; this steady-state protocol aimed to change the excitability of the targeted reflex pathway; reflex size gradually changed over 8-10 weeks. The present study introduces a new protocol, comprising a dynamic protocol that aims to change the functioning of the reflex pathway during a specific phase of a complex movement. Specifically, we down-conditioned the soleus H-reflex during the swing-phase of locomotion in people with hyperreflexia as a result of chronic incomplete SCI. The swing-phase H-reflex, which is absent or very small in neurologically normal individuals, is abnormally large in this patient population. The results were clear. With swing-phase down-conditioning, the H-reflex decreased much faster and farther than did the H-reflex in all previous animal or human studies with the steady-state protocol, and the decrease persisted for at least 6 months after conditioning ended. The H-reflex decrease was accompanied by improvements in walking speed and in the modulation of locomotor electromyograph activity in proximal and distal muscles of both legs. These results provide new insight into the factors controlling spinal reflex conditioning; they suggest that the conditioning protocols targeting reflex function in a specific movement phase provide a promising new opportunity to enhance functional recovery after SCI or in other disorders.
Topics: Animals; Conditioning, Operant; Electromyography; H-Reflex; Humans; Locomotion; Muscle, Skeletal; Recovery of Function; Spinal Cord; Spinal Cord Injuries
PubMed: 31215646
DOI: 10.1113/JP278173 -
PloS One 2020Ocular somatosensory-autonomic reflexes play critical roles in maintaining homeostasis of the eye. The purpose of this study was to investigate the pupil response to...
PURPOSE
Ocular somatosensory-autonomic reflexes play critical roles in maintaining homeostasis of the eye. The purpose of this study was to investigate the pupil response to nociceptive corneal stimuli.
METHODS
A Waterloo-Belmonte pneumatic esthesiometer was used to determine detection thresholds and randomly deliver mechanical and chemical stimuli from levels of detection threshold to twice the threshold in 50% steps to the central cornea of 15 healthy subjects. For each stimulus, imaging of the stimulated/unstimulated eye was performed using two modified/calibrated Logitech c920 digital cameras for 4 seconds each, pre/post stimulus capture. The data were processed with a custom segmentation algorithm to help identify the pupils and pupil diameter was measured using ImageJ software. Pupil dilation response differences between the ipsi- and contralateral eye was analyzed using dependent t-tests. The effect of stimulus intensity, modality and sex of subjects were analyzed using repeated measures.
RESULTS
In mechanical and chemical stimulation experiments, there was no difference in pupil responses between the stimulated eye and the unstimulated eye, (all dependent T-test p > 0.05). On average, pupil diameter increased from baseline as the corneal stimulus intensity increased. This happened regardless of whether mechanical or chemical stimulation occurred (ANOVA p < 0.05). At 200% threshold, pupil diameter was greater than at all stimulus intensities (Tukey HSD, all p < 0.05). Based on stimulus intensity, females had greater pupil diameters than males at levels of 150% threshold and 200% threshold (ANOVA p < 0.05, all Tukey HSD p < 0.05).
CONCLUSION
This study serves as a basis for the characterization of the local stimulus-response neural circuitry relating nociceptive stimuli to autonomic responses and in combination with our work on completely separate autonomic circuits of bulbar conjunctival vessel dilation and reflex tearing suggests that the monotonic measurements of redness, tearing and pupils provide accurate, separable responses that reflect painful stimulus intensity.
Topics: Adult; Carbon Dioxide; Cornea; Female; Humans; Male; Nociception; Physical Stimulation; Pupil; Reflex, Pupillary; Sensory Thresholds; Young Adult
PubMed: 31951635
DOI: 10.1371/journal.pone.0227771 -
Spinal Cord Series and Cases 2020The examination of sacral reflexes provides an important method to differentiate an upper motor neuron vs lower motor neuron spinal cord injury (SCI). Two common sacral... (Review)
Review
The examination of sacral reflexes provides an important method to differentiate an upper motor neuron vs lower motor neuron spinal cord injury (SCI). Two common sacral mediated reflexes used as part of the neurological assessment include the bulbocavernosus reflex (BCR) and anal reflex. As the clinical information from these tests are similar, we suggest that the anal reflex provides a better first option as a non-invasive clinical assessment of sacral reflex status in clinical practice in SCI as the testing for the anal reflex is less intrusive and already being performed as part of the International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI) by pinprick stimulation of the S4-5 dermatome.
Topics: Humans; Neurologic Examination; Reflex; Spinal Cord Injuries
PubMed: 31934354
DOI: 10.1038/s41394-019-0251-3 -
Clinical Chemistry and Laboratory... Dec 2019
Topics: Reflex; Tertiary Healthcare; Thyrotropin
PubMed: 31318690
DOI: 10.1515/cclm-2019-0625 -
Autonomic Neuroscience : Basic &... Dec 2019Type 2 diabetes mellitus (T2DM) leads to exaggerated cardiovascular responses to exercise, in part due to an exaggerated exercise pressor reflex. Accumulating data... (Review)
Review
Type 2 diabetes mellitus (T2DM) leads to exaggerated cardiovascular responses to exercise, in part due to an exaggerated exercise pressor reflex. Accumulating data suggest excessive oxidative stress contributes to an exaggerated exercise pressor reflex in cardiovascular-related diseases. Excessive oxidative stress is also a primary underlying mechanism for the development and progression of T2DM. However, whether oxidative stress plays a role in mediating the exaggerated exercise pressor reflex in T2DM is not known. Therefore, this review explores the potential role of oxidative stress leading to increased activation of the afferent arm of the exercise pressor reflex. Several lines of evidence support direct and indirect effects of oxidative stress on the exercise pressor reflex. For example, intramuscular ROS may directly and indirectly (by attenuating contracting muscle blood flow) increase group III and IV afferent activity. Oxidative stress is a primary underlying mechanism for the development of neuropathic pain, which in turn is associated with increased group III and IV afferent activity. These are the same type of afferents that evoke muscle pain and the exercise pressor reflex. Furthermore, oxidative stress-induced release of inflammatory mediators may modulate afferent activity. Collectively, these alterations may result in a positive feedback loop that further amplifies the exercise pressor reflex. An exaggerated reflex increases the risk of adverse cardiovascular events. Thus, identifying the contribution of oxidative stress could provide a potential therapeutic target to reduce this risk in T2DM.
Topics: Blood Pressure; Cardiovascular Diseases; Diabetes Complications; Diabetes Mellitus, Type 2; Exercise; Humans; Oxidative Stress; Reflex; Sympathetic Nervous System
PubMed: 31669797
DOI: 10.1016/j.autneu.2019.102591 -
PLoS Computational Biology Feb 2022We examine the structure of the visual motion projected on the retina during natural locomotion in real world environments. Bipedal gait generates a complex, rhythmic...
We examine the structure of the visual motion projected on the retina during natural locomotion in real world environments. Bipedal gait generates a complex, rhythmic pattern of head translation and rotation in space, so without gaze stabilization mechanisms such as the vestibular-ocular-reflex (VOR) a walker's visually specified heading would vary dramatically throughout the gait cycle. The act of fixation on stable points in the environment nulls image motion at the fovea, resulting in stable patterns of outflow on the retinae centered on the point of fixation. These outflowing patterns retain a higher order structure that is informative about the stabilized trajectory of the eye through space. We measure this structure by applying the curl and divergence operations on the retinal flow velocity vector fields and found features that may be valuable for the control of locomotion. In particular, the sign and magnitude of foveal curl in retinal flow specifies the body's trajectory relative to the gaze point, while the point of maximum divergence in the retinal flow field specifies the walker's instantaneous overground velocity/momentum vector in retinotopic coordinates. Assuming that walkers can determine the body position relative to gaze direction, these time-varying retinotopic cues for the body's momentum could provide a visual control signal for locomotion over complex terrain. In contrast, the temporal variation of the eye-movement-free, head-centered flow fields is large enough to be problematic for use in steering towards a goal. Consideration of optic flow in the context of real-world locomotion therefore suggests a re-evaluation of the role of optic flow in the control of action during natural behavior.
Topics: Eye Movements; Locomotion; Optic Flow; Reflex, Vestibulo-Ocular; Retina
PubMed: 35192614
DOI: 10.1371/journal.pcbi.1009575 -
Journal of Neurophysiology Jul 2022In this paper, we review the legacy of Gerald (Gerry) Gottlieb in various fields related to the neural control of human movement. His studies on the myotatic (stretch)... (Review)
Review
In this paper, we review the legacy of Gerald (Gerry) Gottlieb in various fields related to the neural control of human movement. His studies on the myotatic (stretch) reflex and postmyotatic responses to ankle joint perturbations paved the way for current explorations of long-loop reflexes and their role in the control of movement. The dual-strategy hypothesis introduced order into a large body of literature on the triphasic muscle activation patterns seen over a variety of voluntary movements in healthy persons. The dual-strategy hypothesis continues to be important for understanding the performance of subjects with disordered motor control. The principle of linear synergy (covariance of joint torques) was an attempt to solve one of the notorious problems of motor redundancy, which remains an important topic in the field. Gerry's attitude toward the equilibrium-point hypothesis varied between rejection and using it to explore patterns of hypothetical control variables and movement variability. The discovery of reciprocal excitation in healthy neonates fostered other studies of changes in spinal cord physiology as motor skills develop. In addition, studies of people with spasticity and the effects of treatment with intrathecal baclofen were crucial in demonstrating the possibility of unmasking voluntary movements after suppression of the hyperreflexia of spasticity. Gerry Gottlieb contributed a significant body of knowledge that formed a solid foundation from which to study a variety of neurological diseases and their treatments, and a more comprehensive and parsimonious foundation to describe the neural control of human movement.
Topics: Electromyography; Humans; Infant, Newborn; Movement; Muscle Contraction; Muscle, Skeletal; Reflex; Reflex, Stretch
PubMed: 35675443
DOI: 10.1152/jn.00141.2022