Modulation Of Spinal Reflexes Research Articles

Effects of A Single Balance Training Session on Neural Excitability in Individuals With Chronic Ankle Instability.

Individuals with chronic ankle instability (CAI) demonstrate reduced spinal reflex modulation and corticospinal excitability of the soleus, which may contribute to decreased balance performance. To determine the effects of a single session of balance training on Spinal-reflexive excitability modulation and corticospinal excitability in those with CAI. Randomized controlled trials. Research laboratory. Thirty participants with CAI were randomly assigned to the balance training (BAL) or control (CON) group. Modulation of soleus spinal-reflexive excitability was measured by calculating relative change in normalized Hoffmann reflexes (ratio of the H-reflex to the M-wave) from prone to single-leg standing. Corticospinal excitability was assessed during single-leg stance using transcranial magnetic stimulation, outcomes of which included active motor threshold (AMT), motor evoked potential, and cortical silent period (CSP). Balance performance was measured with center of pressure velocity in anterior to posterior and medial to lateral directions. Separate 2 × 2 repeated-measures analyses of variance were employed to determine the effect of group (BAL and CON) and time (baseline and posttraining) on each dependent variable. There were significant group by time interactions in the modulation of soleus spinal-reflexive excitability (F1,27 = 4.763, P = .04); CSP at 100% AMT (F1,27 = 4.727, P = .04); and CSP at 120% AMT (F1,27 = 16.057, P < .01). A large effect size suggests increased modulation of spinal-reflexive excitability (d = 0.81 [0.03 to 1.54]) of the soleus in BAL compared with CON at posttest, while CSP at 100% (d = 0.95 [0.17 to 1.70]) and 120% AMT (d = 1.10 [0.29 to 1.84]) was reduced in BAL when compared with CON at posttest. After a single session of balance training, individuals with CAI initiated increases in spinal reflex modulation and corticospinal excitability of the soleus. Thus, individuals with CAI who undergo balance training exhibit positive neural adaptations that are linked to improvements in balance performance.

Dynamic spinal reflex adaptation during locomotor adaptation.

The dynamics and interaction of spinal and supraspinal centers during locomotor adaptation remain vaguely understood. In this work, we use Hoffmann reflex measurements to investigate changes in spinal reflex gains during split-belt locomotor adaptation. We show that spinal reflex gains are dynamically modulated during split-belt locomotor adaptation. During first exposure to split-belt transitions, modulation occurs mostly on the leg ipsilateral to the speed change and constitutes rapid suppression or facilitation of the reflex gains, followed by slow recovery to baseline. Over repeated exposure, the modulation pattern washes out. We further show that reflex gain modulation strongly correlates with correction of leg asymmetry, and cannot be explained by speed modulation solely. We argue that reflex modulation is likely of supraspinal origins and constitutes an integral part of the neural substrate underlying split-belt locomotor adaptation.NEW & NOTEWORTHY This work presents direct evidence for spinal reflex modulation during locomotor adaptation. In particular, we show that reflexes can be modulated on-demand unilaterally during split-belt locomotor adaptation and speculate about reflex modulation as an underlying mechanism for adaptation of gait asymmetry in healthy adults.

Altered cutaneous reflexes to non-noxious stimuli in the triceps surae of people with chronic incomplete spinal cord injury.

Following spinal cord injury (SCI) task-dependent modulation of spinal reflexes are often impaired. To gain insight into the state of the spinal interneuronal pathways following injury, we studied the amplitude modulation of triceps surae cutaneous reflexes to non-noxious stimuli during standing and early-to-mid stance phase of walking in participants with and without chronic incomplete SCI. Reflex eliciting nerve stimulation was delivered to the superficial peroneal, sural, and distal tibial nerves about the ankle. Reflexes were analyzed in the short (SLR, 50-80 ms post stimulation onset) and the medium (MLR, 80-120 ms) latency response windows. Further, the relation between cutaneous and H-reflexes was also examined during standing. In participants without injuries the soleus SLR was modulated task-dependently with nerve specificity, and the soleus and medial gastrocnemius MLRs were modulated task-dependently. In contrast, participants with SCI, no task-dependent or nerve-specific modulation of triceps cutaneous reflexes was observed. The triceps surae cutaneous and H-reflexes were not correlated in either group (r = 0.01-0.37). The presence of cutaneous reflexes but the absence of significant amplitude modulation may suggest impaired function of spinal interneuronal pathways in this population. The lack of correlation between the cutaneous and H-reflexes may suggest that interneurons that are involved in H-reflex modulation and cutaneous reflex modulation do not receive common input, or the impact of the common input is outweighed by other input. Present findings highlight the importance of examining multiple spinal reflexes to better understanding spinal interneuronal pathways that affect motor control in people after SCI.

Utility of transcranial magnetic stimulation in the assessment of spinal cord injury: Current status and future directions.

Comprehensive assessment following traumatic spinal cord injury (SCI) is needed to improve prognostication, advance the understanding of the neurophysiology and better targeting of clinical interventions. The International Standards for Neurological Classification of Spinal Cord Injury is the most common clinical examination recommended for use after a SCI. In addition, there are over 30 clinical assessment tools spanning across different domains of the International Classification of Functioning, Disability, and Health that have been validated and recommended for use in SCI. Most of these tools are subjective in nature, have limited value in predicting neurologic recovery, and do not provide insights into neurophysiological mechanisms. Transcranial magnetic stimulation (TMS) is a non-invasive neurophysiology technique that can supplement the clinical assessment in the domain of body structure and function during acute and chronic stages of SCI. TMS offers a better insight into neurophysiology and help in better detection of residual corticomotor connectivity following SCI compared to clinical assessment alone. TMS-based motor evoked potential and silent period duration allow study of excitatory and inhibitory mechanisms following SCI. Changes in muscle representations in form of displacement of TMS-based motor map center of gravity or changes in the map area can capture neuroplastic changes resulting from SCI or following rehabilitation. Paired-pulse TMS measures help understand the compensatory reorganization of the cortical circuits following SCI. In combination with peripheral stimulation, TMS can be used to study central motor conduction time and modulation of spinal reflexes, which can be used for advanced diagnostic and treatment purposes. To strengthen the utility of TMS in SCI assessment, future studies will need to standardize the assessment protocols, address population-specific concerns, and establish the psychometric properties of TMS-based measurements in the SCI population.

Temporal Profile of Descending Cortical Modulation of Spinal Excitability: Group and Individual-Specific Effects.

Sensorimotor control is modulated through complex interactions between descending corticomotor pathways and ascending sensory inputs. Pairing sub-threshold transcranial magnetic stimulation (TMS) with peripheral nerve stimulation (PNS) modulates the Hoffmann’s reflex (H-reflex), providing a neurophysiologic probe into the influence of descending cortical drive on spinal segmental circuits. However, individual variability in the timing and magnitude of H-reflex modulation is poorly understood. Here, we varied the inter-stimulus interval (ISI) between TMS and PNS to systematically manipulate the relative timing of convergence of descending TMS-induced volleys with respect to ascending PNS-induced afferent volleys in the spinal cord to: (1) characterize effective connectivity between the primary motor cortex (M1) and spinal circuits, mediated by both direct, fastest-conducting, and indirect, slower-conducting descending pathways; and (2) compare the effect of individual-specific vs. standard ISIs. Unconditioned and TMS-conditioned H-reflexes (24 different ISIs ranging from −6 to 12 ms) were recorded from the soleus muscle in 10 able-bodied individuals. The magnitude of H-reflex modulation at individualized ISIs (earliest facilitation delay or EFD and individual-specific peak facilitation) was compared with standard ISIs. Our results revealed a significant effect of ISI on H-reflex modulation. ISIs eliciting earliest-onset facilitation (EFD 0 ms) ranged from −3 to −5 ms across individuals. No difference in the magnitude of facilitation was observed at EFD 0 ms vs. a standardized short-interval ISI of −1.5 ms. Peak facilitation occurred at longer ISIs, ranging from +3 to +11 ms. The magnitude of H-reflex facilitation derived using an individual-specific peak facilitation was significantly larger than facilitation observed at a standardized longer-interval ISI of +10 ms. Our results suggest that unique insights can be provided with individual-specific measures of top-down effective connectivity mediated by direct and/or fastest-conducting pathways (indicated by the magnitude of facilitation observed at EFD 0 ms) and other descending pathways that encompass relatively slower and/or indirect connections from M1 to spinal circuits (indicated by peak facilitation and facilitation at longer ISIs). By comprehensively characterizing the temporal profile and inter-individual variability of descending modulation of spinal reflexes, our findings provide methodological guidelines and normative reference values to inform future studies on neurophysiological correlates of the complex array of descending neural connections between M1 and spinal circuits.

Muscle-Specific Modulation of Spinal Reflexes in Lower-Limb Muscles during Action Observation with and without Motor Imagery of Walking.

Action observation (AO) and motor imagery (MI) are useful techniques in neurorehabilitation. Previous studies have reported that AO and MI facilitate corticospinal excitability only in those muscles that are active when actually performing the observed or imagined movements. However, it remained unclear whether spinal reflexes modulate multiple muscles simultaneously. The present study focused on AO and MI of walking and aimed to clarify their effects on spinal reflexes in lower-limb muscles that are recruited during actual walking. Ten healthy males participated in the present study. Spinal reflex parameters evoked by transcutaneous spinal cord stimulation were measured from five lower-limb muscles during rest, AO, and AO combined with MI (AO + MI) conditions. Our results showed that spinal reflexes were increased in the tibialis anterior and biceps femoris muscles during AO and in the tibialis anterior, soleus, and medial gastrocnemius muscles during AO + MI, compared with resting condition. Spinal reflex parameters in the vastus medialis muscle were unchanged. These results indicate the muscle-specific modulations of spinal reflexes during AO and AO + MI. These findings reveal the underlying neural activities induced by AO, MI, and their combined processes.

The Short-Term Effect of Slope Walking on Soleus H-Reflexes in People with Multiple Sclerosis

Downslope walking (DSW) causes H-reflex depression in healthy adults, and thus may hold promise for inducing spinal reflex plasticity in people with Multiple Sclerosis (PwMS). The study purpose was to test the hypothesis that DSW will cause acute depression of spinal excitability in PwMS. Soleus H-reflexes were measured in PwMS (n = 18) before and after 20 min of treadmill walking during three visits. Participants walked on a different slope each visit [level: 0% level walking (LW), upslope: +7.5% treadmill walking with an upslope (USW) or downslope: −7.5% (DSW)]. The soleus Hmax/Mmax ratio was used to measure spinal excitability. Heart rate and ratings of perceived exertion (RPE) were measured during walking. DSW induced the largest change in spinal excitability (a 26.7% reduction in soleus Hmax/Mmax (p = 0.001)), although LW also reduced Hmax/Mmax (-5.3%, p = 0.05). Heart rate (p < 0.001) was lowest for DSW, and RPE for DSW did not exceed “Fairly light”. DSW evokes short-term spinal plasticity in PwMS, while requiring no greater effort than LW. Our results suggest that PwMS retain the capacity for DSW-induced short-term spinal reflex modulation previously found in healthy adults. These results may provide a foundation for further investigation of long-term effects of DSW on spinal reflex plasticity and functional ability in PwMS.

Sacral neuromodulation for treatment of overactive bladder: a review

Sacral neuromodulation (SNM) therapy is an established third line therapeutic option for the treatment of urgency urinary incontinence, urgency-frequency and chronic non-obstructive urinary retention. The continuous stimulation of the sacral root S3 with an electrode connected to an implanted pulse generator (IPG) may influence detrusor and sphincter activity and improve lower urinary tract symptoms. The mechanism of action is not completely understood and seems to be based on the modulation of spinal cord reflexes and brain centers involved in lower urinary tract function. It is implanted with a minimally invasive technique that can be performed under local anesthesia and includes a test phase that precedes the definitive implantation of the pulse generator. When compared to the standard pharmacological therapy, neuromodulation promoted better results both in the partial improvement of overactive bladder (OAB) symptoms and total continence. Moreover, sexual function, quality of life and depressive symptoms may also improve in patients with OAB that undergo SNM. However, SNM is associated with significant rates of adverse events and need for surgical revisions, requiring continuous medical attention.

Serotonin transporter (5‐HTTLPR) genotypes and trinucleotide repeats of androgen receptor exert a combinatorial effect on hormonal milieu in patients with lifelong premature ejaculation

Premature ejaculation is one of the most common sexual disorders in men due to uncontrolled modulation of spinal reflexes controlled by cortico-limbic centers in the brain. In this study, we investigate the combinatorial effects of trinucleotide repeats of androgen receptor and allelic variants of the 5-HTTLPR gene on sex steroids, hypophyseal hormones, sexual performance, and premature ejaculation assessment parameters among evidence-based lifelong premature ejaculation subjects. A total of 271 outpatients (age 26.6±1.9) consulting for evidence-based lifelong premature ejaculatory dysfunction were selected in this study. The control group consists of 155 men with normal IELT (>4min). The study revealed that the subjects who have the highest (≥26) CAG stretches depicted a significantly higher serum oxytocin levels (102.1pg/ml; n=126, p<0.001) compared with the control group (71.2 pg/ml; n = 75, p = <0.001) and patients which have medium (22-25) and short (≤21) CAG stretches (76.63ng/ml; n=64, p<0.001 vs. 77.4ng/ml; n=81, p<0.001). Almost 33 (26.1%) lifelong premature ejaculatory patients had AR variant of longer (≥26) CAG repeats was homozygous for S alleles (SS), 45 (35.7%) was homozygous for L allele (LL), and 48 (38%) had the L/S or S/L genotype of 5-HTTLPR gene. Homozygous (SS) alleles have a significant positive correlation (r=0.44, p<0.0001) with the high score of BDI-II (39.1, n=126, p<0.001). However, LL alleles have shown a significant positive correlation with PEDT (r=0.46, p<0.001) and negative correlation with self-estimated IELT and intercourse satisfaction (r=-0.35, p<0.001). The innovative study design elaborates that androgen receptor trinucleotide repeats and 5-HTTLPR genotypes have combinatorial impact on hormonal milieu and sexual function regarding evidence-based lifelong premature ejaculatory dysfunction patients.

Task-dependent modulation of spinal and transcortical stretch reflexes linked to motor learning rate.

It is generally believed that task-dependent control of body configuration ("posture") is achieved by adjusting voluntary motor activity and transcortical "long-latency" reflexes. Spinal monosynaptic circuits are thought not to be engaged in such task-level control. Similarly, being in a state of motor learning has been strongly associated only with an upregulation of feedback responses at transcortical latencies and beyond. In two separate experiments, the current study examined the task-dependent modulation of stretch reflexes by perturbing the hand of human subjects while they were waiting for a "Go" signal to move at the different stages of a classic kinematic learning task (visuomotor rotation). Although the subjects had to resist all haptic perturbations equally across task stages, the study leveraged that task-dependent feedback controllers may already be "loaded" at the movement anticipation stage. In addition to an upregulation of reflex gains during early exposure to the visual distortion, I found a relative inhibition of reflex responses in the "washout" stage (sensory realignment state). For more distal muscles (brachioradialis) this inhibition also extended to the monosynaptic reflex response ("R1"). Moreover, these R1 gains reflected individual motor learning performance in the visuomotor task. The results demonstrate that the system's "control policy" in visuomotor adaptation can also include inhibition of proprioceptive reflexes, and that aspects of this policy can affect monosynaptic spinal circuits. The latter finding suggests a novel form of state-related control, probably realized by independent control of fusimotor neurons, through which segmental circuits can tune to higher-level features of a sensorimotor task. (PsycINFO Database Record

Neuromodulation bei Harnblasenfunktionsstörungen

Neuromodulative procedures such as transcutaneous electrical nerve stimulation (TENS), transcutaneous/percutaneous tibial nerve stimulation (TTNS/PTNS), and sacral neuromodulation (SNM) are promising second-line treatments for refractory lower urinary tract dysfunction. Using these therapies, both storage and voiding disorders but also bowel dysfunction might be successfully treated. Although the mechanism of action of neuromodulation is not well understood, it seems to involve modulation of spinal cord reflexes and brain networks by peripheral afferents (genital/rectal, tibial and sacral afferents in the case of TENS, TTNS/PTNS, and SNM, respectively). Neuromodulative procedures might also be highly effective in the most desperate situations and further relevant developments are expected so that these innovative techniques will most likely become even more important in urology.

Modulation of spinal inhibitory reflexes depends on the frequency of transcutaneous electrical nerve stimulation in spastic stroke survivors

Neurophysiological studies in healthy subjects suggest that increased spinal inhibitory reflexes from the tibialis anterior (TA) muscle to the soleus (SOL) muscle might contribute to decreased spasticity. While 50 Hz is an effective frequency for transcutaneous electrical nerve stimulation (TENS) in healthy subjects, in stroke survivors, the effects of TENS on spinal reflex circuits and its appropriate frequency are not well known. We examined the effects of different frequencies of TENS on spinal inhibitory reflexes from the TA to SOL muscle in stroke survivors. Twenty chronic stroke survivors with ankle plantar flexor spasticity received 50-, 100-, or 200-Hz TENS over the deep peroneal nerve (DPN) of the affected lower limb for 30 min. Before and immediately after TENS, reciprocal Ia inhibition (RI) and presynaptic inhibition of the SOL alpha motor neuron (D1 inhibition) were assessed by adjusting the unconditioned H-reflex amplitude. Furthermore, during TENS, the time courses of spinal excitability and spinal inhibitory reflexes were assessed via the H-reflex, RI, and D1 inhibition. None of the TENS protocols affected mean RI, whereas D1 inhibition improved significantly following 200-Hz TENS. In a time-series comparison during TENS, repeated stimulation did not produce significant changes in the H-reflex, RI, or D1 inhibition regardless of frequency. These results suggest that the frequency-dependent effect of TENS on spinal reflexes only becomes apparent when RI and D1 inhibition are measured by adjusting the amplitude of the unconditioned H-reflex. However, 200-Hz TENS led to plasticity of synaptic transmission from the antagonist to spastic muscles in stroke survivors.

Effects of postural and voluntary muscle contraction on modulation of the soleus H reflex by transcranial magnetic stimulation.

Modulation of spinal reflexes depends largely on the integrity of the corticospinal tract. A useful method to document the influence of descending tracts on reflexes is to examine the effects of transcranial magnetic stimulation (TMS) on the soleus H reflex elicited by posterior tibial nerve electrical stimuli (PTS). In 12 healthy volunteers, we investigated how postural or voluntary muscle contraction modified such descending modulation. We first characterized the effects of TMS at 95 % of motor threshold for leg responses on the H reflex elicited by a preceding PTS at inter-stimuli intervals (ISIs) between 0 and 120 ms at rest and, then, during voluntary plantar flexion (pf), dorsal flexion (df), and standing still (ss). During pf, there was an increase in the facilitation of the H reflex at ISIs 0-20 ms. During df, there were no effects of TMS on the H reflex. During ss, there was inhibition at ISIs 40-60 ms. Our observations suggest that muscle contraction prevails over the baseline effects of TMS on the soleus H reflex. While contraction of the antagonist (df) suppressed most of the effects, contraction of the agonist had different effects depending on the type of activity (pf or ss). The characterization of the interaction between descending corticospinal volleys and segmental peripheral inputs provides useful information on motor control for physiological research and further understanding of the effects of spinal cord lesions.

Neuromodulación en aneyaculación. Reporte de caso revisión de la literatura

Introduction and objectivesSacral root neuromodulation (SRN) is a procedure used to treat urinary function, as well as bowel and sexual disorders. In sexual disorders, there is some data suggesting benefits in erectile dysfunction, with very little evidence on ejaculation disorders. The objective of this report is to review the theory of SRN operation and its indications in order to propose a hypothesis on the mechanism and why our patient improved his ejaculation disorder after the SRN procedure. We suggest the SRN as an alternative treatment in the management of refractory anejaculation. Methods and materialsReview of patient's medical chart. A literature search was performed using MEDLINE and OVID. The search was limited to papers published in the last 10 years. MESH terms used were “sacral plexus”, “sacral region”, “ejaculation”, “neurobiology”, “spinal cord stimulation”, “transcutaneous electric nerve stimulation”, and also a non-MESH term “neuromodulation”. ResultsWe present the first report of anejaculation, secondary to pelvic surgical dissection in a young patient with a previously normal sexual life. Ejaculation improved significantly after the SRN procedure. The mechanism of action of SRN is not entirely known. It is possible that afferent electrical stimulation allows the modulation of spinal reflexes by restoring the balance between inhibition and activation at a central level. It has been used in the management of urinary, bowel, sexual, and nervous disorders. Based on this positive response, our hypothesis is that the surgical procedure altered the transmission of efferent signals of the pelvic nerves. The SRN procedure could improve the regulation of spinal reflexes and transmission of ejaculatory signals mediated by serotonin and noradrenaline transported by pelvic and pudenda nerves. ConclusionsThe SRN is presented as an alternative in the management of anejaculation despite the lack of evidence to support the standardization of the procedure.© 2012 Sociedad Colombiana de Urología. Published by Elsevier España, S.L. All rights reserved.

Aging causes a reorganization of cortical and spinal control of posture

Classical studies in animal preparations suggest a strong role for spinal control of posture. In humans it is now established that the cerebral cortex contributes to postural control of unperturbed and perturbed standing. The age-related degeneration and accompanying functional changes in the brain, reported so far mainly in conjunction with simple manual motor tasks, may also affect the mechanisms that control complex motor tasks involving posture. This review outlines the age-related structural and functional changes at spinal and cortical levels and provides a mechanistic analysis of how such changes may be linked to the behaviorally manifest postural deficits in old adults. The emerging picture is that the age-related reorganization in motor control during voluntary tasks, characterized by differential modulation of spinal reflexes, greater cortical activation and cortical disinhibition, is also present during postural tasks. We discuss the possibility that this reorganization underlies the increased coactivation and dual task interference reported in elderly. Finally, we propose a model for future studies to unravel the structure-function-behavior relations in postural control and aging.

The Effects of State Anxiety on Hoffman (H) Reflex Parameters in Female University Students

Background and Aim: Anxiety, as one of the most common and costly problems in Iran and all over the world, comprises both physical and mental disorders. Previous research has proposed that spinal reflex modulation may mediate anxiety-related changes in postural control. This study aimed to investigate if the H-reflex parameters are influenced by state anxiety. Materials and Methods: A group of 20 healthy female university students with a low anxiety score (lower than 42, based upon the Schpilberger’s questionnaire) were recruited in this study and the Hreflex of their Soleus muscle was recorded in four positions. The tested positions included the standard prone lying (the reference position), standing on level ground; and two stability threatening positions including standing on the center and at the edge of a one-meter height stool. The outcome measures were the latency, amplitude and the amplitude needed to record the reflex. Results: No significant differences were shown in the latency of the H-reflex among the four tested positions (p>0.05). In terms of the amplitude of the reflex, however, significant differences were found between all positions when compared to the reference position (prone lying) (p=0.001). There are significant differences among all four positions in amplitude needed to record the H-reflex (p=0.034), while the Bonferoni test revealed the significant difference only between the position of standing at the edge of the height relative to the standard prone lying position (p=0.041). Conclusion: The results of this study showed that any postural perturbation results in brain activities and affects more on the amplitudes rather than the latency of the H-reflex. These findings may be helpful in a better understanding of the standing balance in healthy people and people suffering from postural instabilities, fear of falling, elderly persons and also hemiplegic patients. Keywords: State Anxiety, H-Reflex, Stability threatening conditions

The effect of active pedaling combined with electrical stimulation on spinal reciprocal inhibition

ObjectivePedaling is widely used for rehabilitation of locomotion because it induces muscle activity very similar to locomotion. Afferent stimulation is important for the modulation of spinal reflexes. Furthermore, supraspinal modulation plays an important role in spinal plasticity induced by electrical stimulation. We, therefore, expected that active pedaling combined with electrical stimulation could induce strong after-effects on spinal reflexes. DesignTwelve healthy adults participated in this study. They were instructed to perform 7min of pedaling. We applied electrical stimulation to the common peroneal nerve during the extension phase of the pedaling cycle. We assessed reciprocal inhibition using a soleus H-reflex conditioning-test paradigm. The magnitude of reciprocal inhibition was measured before, immediately after, 15 and 30min after active pedaling alone, electrical stimulation alone and active pedaling combined with electrical stimulation (pedaling+ES). ResultsThe amount of reciprocal inhibition was significantly increased after pedaling+ES. The after-effect of pedaling+ES on reciprocal inhibition was more prominent and longer lasting compared with pedaling or electrical stimulation alone. ConclusionsPedaling+ES could induce stronger after-effects on spinal reciprocal inhibitory neurons compared with either intervention alone. Pedaling+ES might be used as a tool to improve locomotion and functional abnormalities in the patient with central nervous lesion.

Motor consequences of experimentally induced limb pain: A systematic review

Compelling evidence exists that pain may affect the motor system, but it is unclear if different sources of peripheral limb pain exert selective effects on motor control. This systematic review evaluates the effects of experimental (sub)cutaneous pain, joint pain, muscle pain and tendon pain on the motor system in healthy humans. The results show that pain affects many components of motor processing at various levels of the nervous system, but that the effects of pain are largely irrespective of its source. Pain is associated with inhibition of muscle activity in the (painful) agonist and its non-painful antagonists and synergists, especially at higher intensities of muscle contraction. Despite the influence of pain on muscle activation, only subtle alterations were found in movement kinetics and kinematics. The performance of various motor tasks mostly remained unimpaired, presumably as a result of a redistribution of muscle activity, both within the (painful) agonist and among muscles involved in the task. At the most basic level of motor control, cutaneous pain caused amplification of the nociceptive withdrawal reflex, whereas insufficient evidence was found for systematic modulation of other spinal reflexes. At higher levels of motor control, pain was associated with decreased corticospinal excitability. Collectively, the findings show that short-lasting experimentally induced limb pain may induce immediate changes at all levels of motor control, irrespective of the source of pain. These changes facilitate protective and compensatory motor behaviour, and are discussed with regard to pertinent models on the effects of pain on motor control.

Neuromuscular Recovery after Medial Collateral Ligament Disruption and Eccentric Rehabilitation Program

Medial collateral ligament (MCL) rupture of the knee joint frequently occurs during sport activities. However, the optimal rehabilitation strategy after such lesion is unknown. The aim of this study was to assess the effects of progressive eccentric rehabilitation program on neuromuscular deficits induced by MCL transection. Rats were randomized as follows: (i) control group (C, n = 10) without any surgery; (ii) lesion groups in which neuromuscular measurements were made 1 (L1, n = 10) and 3 wk (L3, n = 9) after MCL transection by a 15- to 20-min surgery (this group was designed to determine changes induced by the MCL transection); and (iii) eccentric group (ECC, n = 7) in which rats performed a progressive 2-wk eccentric rehabilitation program beginning 1 wk after MCL transection surgery. Dynamic functional assessments were performed at weeks 1 and 3 after the MCL transection by measuring the maximal and minimal knee angles during the stance phase of the gait cycle. Neuromuscular measurements included 1) modulation of H-reflex in response to a 10-mM KCl injection, 2) analysis of the twitch relaxation properties of the quadriceps muscle, and 3) recording of metabosensitive and mechanosensitive afferents activity in response to chemical injections and to tendon patellar vibrations, respectively. Our results indicated that H-reflex modulation induced by metabosensitive afferents was disturbed by MCL transection without any recovery despite rehabilitation program. Responses of both metabosensitive and mechanosensitive muscle afferents, as well as the muscle relaxation properties, were fully recovered after the eccentric rehabilitation program. Our results directly indicated an influence of progressive eccentric program on muscle afferents response after MCL section but apparently not for spinal reflex modulation.

Sex-Specific Strategies in Spinal Reflex Modulation during a Secondary Task

Attenuation of lower extremity (soleus) spinal reflexes has been documented during upper extremity motor tasks such as arm cycling. It is unknown whether similar neural coupling occurs in soleus spinal reflexes during an upper extremity task involving mental concentration and only minimal movement. PURPOSE: To assess soleus H reflex excitability in males and females during an attention-consuming secondary task. METHODS: Soleus H reflex recruitment curves were obtained from 13 male (25.6 ± 4.6 yrs; BMI 24.9 ± 3.8 kg/m2) and 16 female (25.1 ± 3.4 yrs; BMI 23.8 ± 2.4 kg/m2) volunteers. A stimulating electrode and dispersal pad were affixed to the participant's dominant leg over the tibial nerve and proximal to the patella, respectively. Disposable surface EMG (Ag/AgCl) electrodes recorded soleus peak-to-peak H reflex amplitude. With the participant positioned in a reclining chair fitted with a foot rest, soleus H reflexes were elicited at gradually increasing stimulus intensities, from H reflex threshold to maximal H reflex (H-max). Next, a similar recruitment curve was obtained while the participant typed a predetermined sequence of 3-letter nonsense words on a laptop computer. The dependent variables were H-max and the slope of the linear ascending portion (H-slope) of the recruitment curve, as determined using least squares regression. H-max and H-slope were analyzed using separate 2[testing position] × 2[sex] ANOVA. RESULTS: H-max was reduced in both males and females during the secondary task (control: 8.3 ± 2.7, typing 7.5 ± 2.8; p<.001). For H-slope, males and females demonstrated different responses. Males showed a significant reduction in H slope (control: 6.14 ± 1.7, typing 4.86 ± 2.0; p=.018) while females demonstrated a significant increase in H slope (control: 5.95 ± 1.8; typing 6.20 ± 3.0; p=.024). CONCLUSION: Soleus H-max is attenuated by an attention-consuming task in both sexes. H-slope was attenuated in males, but facilitated in females, suggesting potential sex differences in lower-extremity reflex modulation when attention is diverted to a secondary task.