Stimulation Of Common Peroneal Nerve Research Articles

The Orthotic Effects of Different Functional Electrical Stimulation Protocols on Walking Performance in Individuals with Incomplete Spinal Cord Injury: A Case Series.

Functional electrical stimulation (FES) of paralyzed muscles can facilitate walking after spinal cord injury (SCI). To test the orthotic effects of different FES walking protocols on lower joint kinematics and walking speed. Three adults with incomplete SCI participated in this study. Their lower extremity motor scores and 10-meter walk test results were as follows: subject A: 50, 1.05 m/s, subject B: 44, 0.29 m/s, and subject C: 32, 0.27 m/s. Participants completed four conditions of over-ground walking including no FES and three bilateral FES-walking protocols as follows: multi-muscle stimulation (stimulation of quadriceps and gastrocnemius in the stance phase, and hamstring and tibialis anterior in the swing phase), drop foot (tibialis anterior stimulation), and flexor withdrawal (common peroneal nerve stimulation). The FES system obtained gait phase information from foot switches located under the individuals' heels. Three-dimensional kinematic analysis was undertaken to measure minimum toe clearance (MTC); ankle, knee, and hip range of motion (ROM); stride length; and stride speed. Compared to no-FES walking, MTC increased during drop foot (all subjects), flexor withdrawal (subjects A and B), and multi-muscle stimulation (subjects B and C) protocols. A significant decrease in ankle ROM was seen with drop foot (all subjects), flexor withdrawal (subjects A), and multi-muscle stimulation (subjects A and C) protocols. Hip ROM increased with drop foot (subjects B and C), flexor withdrawal (subject B), and multi-muscle stimulation (subject C) protocols. Three FES walking protocols induced positive kinematic changes as indicated by increased MTC, decreased ankle ROM, and increased hip ROM during walking in subjects with incomplete SCI.

Altered regulation of Ia afferent input during voluntary contraction in humans with spinal cord injury.

Sensory input converging on the spinal cord contributes to the control of movement. Although sensory pathways reorganize following spinal cord injury (SCI), the extent to which sensory input from Ia afferents is regulated during voluntary contraction after the injury remains largely unknown. To address this question, the soleus H-reflex and conditioning of the H-reflex by stimulating homonymous [depression of the soleus H-reflex evoked by common peroneal nerve (CPN) stimulation, D1 inhibition] and heteronymous (d), [monosynaptic Ia facilitation of the soleus H-reflex evoked by femoral nerve stimulation (FN facilitation)] nerves were tested at rest, and during tonic voluntary contraction in humans with and without chronic incomplete SCI. The soleus H-reflex size increased in both groups during voluntary contraction compared with rest, but to a lesser extent in SCI participants. Compared with rest, the D1 inhibition decreased during voluntary contraction in controls but it was still present in SCI participants. Further, the FN facilitation increased in controls but remained unchanged in SCI participants during voluntary contraction compared with rest. Changes in the D1 inhibition and FN facilitation were correlated with changes in the H-reflex during voluntary contraction, suggesting an association between outcomes. These findings provide the first demonstration that the regulation of Ia afferent input from homonymous and heteronymous nerves is altered during voluntary contraction in humans with SCI, resulting in lesser facilitatory effect on motor neurons.

Effects of Dry Needling on Spinal Reciprocal Inhibition

<h3>Research Objectives</h3> Spinal reciprocal inhibition is an important spinal mechanism of motor control. It is often impaired in persons after stroke, negatively impacting locomotion; at the same time, it changes in response to therapeutic interventions (e.g., FES). An increasing number of physical therapists worldwide have been administering trigger point deep dry needling (DDN) to treat post-stroke spasticity. Yet, currently, effects of DDN on spinal somatosensory processing are not well understood. Thus, to understand neurophysiological mechanisms of DDN, we are investigating the effects of DDN on spinal pathways in persons with and without stroke. <h3>Design</h3> Before and 0, 90 minutes, and 72 hours after DDN of the medial gastrocnemius (MG) at myofascial trigger points, reciprocal inhibition of the soleus, MG and lateral gastrocnemius (LG) was examined while the participant stood and maintained his/her standing posture and triceps muscle activity. Passive ankle range of motion (ROM) was also measured before and after DDN. <h3>Setting</h3> University. <h3>Participants</h3> 11 adults 22-57 years old (median 37.5) without known neurological conditions. <h3>Interventions</h3> Trigger point dry needling to medial gastrocnemius <h3>Main Outcome Measures</h3> Reciprocal inhibition of ongoing muscle activity elicited by common peroneal nerve (CPN) stimulation. ROM. <h3>Results</h3> In the MG and LG, there was no systematic changes in the amount of inhibition across participants or measurement times. Soleus inhibition elicited by suprathreshold CPN stimulation was increased significantly at 0 minute and 72 hours post DDN (p>0.05). Ankle dorsiflexion ROM was increased by 4 deg at 0 minutes and 72 hours post DDN. <h3>Conclusions</h3> DDN alters soleus inhibition, which may partially explain increased ankle ROM post DDN. In order to understand how DDN affects reciprocal inhibition in the stroke-impaired CNS, studies of individuals after stroke are currently underway. <h3>Author(s) Disclosures</h3> The authors have no conflicts of interest to declare.

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

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

P23-F Re-examining the origin of medium latency reflex response of soleus using single motor units

Background This study is inquiring the origin of the medium latency reflex response (MLR) that occurs in soleus muscle when common peroneal nerve is electrically stimulated. Material and methods In total, 23 SingleMUs from 9 males were obtained. During SMU recruitment, 308 ± 141 stimuli were delivered. We investigated the duration of the inhibitory postsynaptic potential (IPSP) and excitatory postsynaptic potential (EPSP). Results Common peroneal nerve stimulation resulted in M-response at SEMG of TA muscle and MLR in SOL-SEMG as well as accumulation of SMUs between 50 and 120 ms after the stimulus. A reduction in firing probability of SMUs was also observed and the reduction in discharge rate continued much longer than the spike reduction probability in PSTH and CUSUM. This reduction in discharge rate was followed by an increased discharge rate of SMUs. Duration of the IPSP obtained at PSF, 24.5 ± 6.3 ms, and the duration of EPSP, i.e. MLR, in PSF was found as 119.3 ± 54.3 The latency of EPSP was found higher in PSF and SEMG as 68.3 ± 9.9 ms and 74.5 ± 9.7 ms, than PSTH and MMU which were 56.3 ± 4.6 ms and 57.6 ± 4.2 ms, respectively. Conclusions There was a genuine Ia reciprocal inhibition followed by a stretch-induced reflex response in the SOL. The first response was due to the well-known Ia-IPSP pathway connecting antagonist muscles and the second response, the so-called MLR in the literature, was an indirect stretch reflex response caused by the M-response in the TA muscle. This Project (3135) was supported by Akdeniz University Scientific Research Unit .

Medium latency excitatory reflex of soleus re-examined.

We aimed to study the receptor origin and postsynaptic potential profile of the medium latency reflex (MLR) response that develops in the soleus muscle when common peroneal nerve of antagonist tibialis anterior (TA) muscle is electrically stimulated. To achieve this aim, we electrically stimulated common peroneal nerve and recorded surface electromyography (SEMG) responses of soleus and TA muscles of informed volunteers. Additionally, we recorded intramuscular EMG from the soleus muscle. Stimulation of common peroneal nerve induced a direct motor response (M-response) in the TA and MLR in SEMG of the soleus. Using voluntarily-activated single motor units (SMUs) from the soleus muscle we noted that there were two distinct responses following the stimulus. The first response was a reciprocal inhibitory reflex probably originating from the antagonist muscle spindle primary (Ia) afferents. This was followed by an indirect reflex response activated by the contraction of the TA muscle during the M-response. This contraction generated a rapid acceleration in the direction of dorsiflexion hence inducing a stretch stimulus on soleus muscle. The response of soleus to this stimulus was a stretch reflex. We suggest that this stretch reflex is the main contributor to the so-called soleus MLR in the literature. This study illustrated the importance of using SMUs and also using discharge-rate based analysis for closely examining previously 'established' reflexes.

Presynaptic inhibition mechanisms may subserve the spinal excitability modulation induced by neuromuscular electrical stimulation

This study aimed at deciphering the origins of spinal excitability modulation that follows neuromuscular electrical stimulation (NMES). Ten participants (age: 24.6 ± 4.2 years) performed 2 randomized NMES sessions on plantar flexors with frequencies of stimulations of 20 or 100 Hz (pulse width: 1 ms) at 20% of maximal voluntary contraction (MVC). Before and after each session, the posterior tibial nerve was stimulated to record H-reflex of soleus (SOL), gastrocnemius medialis (GM) and gastrocnemius lateralis (GL). D1 presynaptic inhibition was assessed by conditioning H reflex with prior common peroneal nerve stimulation. Resting H-reflex of SOL decreased after both protocols, but in a greater extent following the 100 Hz session (100 Hz: −34.6 ± 7.3%, 20 Hz: −17.1 ± 3.8%; P = 0.002), accompanied by an increase of presynaptic inhibition (+22 ± 5.8% at 100 Hz vs. +8 ± 3.7% at 20 Hz, P < 0.001). GM and GL spinal excitability and presynaptic inhibition were also altered after NMES, but in a similarly extent after 20 Hz and 100 Hz protocols. Neuromuscular fatigue following a single session of NMES involves spinal presynaptic circuitry, even at low stimulation frequency. The spinal sensitivity to NMES seems also muscle dependent.

Dynamic Fatigue Does Not Alter Soleus H-Reflexes Conditioned by Homonymous or Heteronymous Pathways.

H-reflex depression (diminution of amplitude after a conditioning stimulus) is mediated presynaptically and therefore can help distinguish central versus peripheral mechanisms of fatigue. We examined the effects of a dynamic exercise protocol on H-reflex depression using two conditioning methods: homonymous conditioning (paired-pulse tibial nerve stimulation); and heteronymous conditioning (common peroneal nerve stimulation). Ten subjects performed dynamic contractions of the soleus muscle through 30° ankle range of motion. The concentric phase required a target force of 10% of maximum voluntary isometric contraction (MVIC) and the eccentric phase force target was 80% MVIC. Fatigue persisted for >20 min after cessation of the exercise. Compared with prefatigue values, the dynamic fatigue protocol did not increase presynaptic inhibition after either homonymous or heteronymous conditioning. Peak to peak amplitude of unconditioned H-reflexes was likewise unchanged despite a long term depression of muscle force (long duration fatigue). These results suggest that persistent fatigue after dynamic exercise is attributed to muscle changes and not altered spinal mechanisms.

Short-term effect of electrical nerve stimulation on spinal reciprocal inhibition during robot-assisted passive stepping in humans.

The purpose of this study was to investigate the effect of electrical stimulation to the common peroneal nerve (CPN) on the spinal reflex and reciprocal inhibition (RI) during robot-assisted passive ground stepping (PGS) in healthy subjects. Five interventions were applied for 30 min in healthy subjects: PGS alone; strong CPN stimulation [50% of the maximal tibialis anterior (TA) M-wave, functional electrical stimulation (FES)] alone; weak CPN stimulation [just above the MT for the TA muscle, therapeutic electrical stimulation (TES)] alone; PGS with FES; and PGS with TES. FES and TES were applied intermittently to the CPN at 25 Hz. The soleus (Sol) H-reflex and RI, which was assessed by conditioning the Sol H-reflex with CPN stimulation, were investigated before (baseline), and 5, 15 and 30 min after each intervention. The amplitudes of the Sol H-reflex were not significantly different after each intervention as compared with the baseline values. The amounts of RI were significantly decreased 5 min after PGS with FES as compared with the baseline values, whereas they were significantly increased 5 and 15 min after PGS with TES. The other interventions did not affect the amount of RI. These results suggest that interventions that combined PGS with CPN stimulation changed the spinal RI in an intensity-dependent manner.

Locomotor training improves reciprocal and nonreciprocal inhibitory control of soleus motoneurons in human spinal cord injury.

Pathologic reorganization of spinal networks and activity-dependent plasticity are common neuronal adaptations after spinal cord injury (SCI) in humans. In this work, we examined changes of reciprocal Ia and nonreciprocal Ib inhibition after locomotor training in 16 people with chronic SCI. The soleus H-reflex depression following common peroneal nerve (CPN) and medial gastrocnemius (MG) nerve stimulation at short conditioning-test (C-T) intervals was assessed before and after training in the seated position and during stepping. The conditioned H reflexes were normalized to the unconditioned H reflex recorded during seated. During stepping, both H reflexes were normalized to the maximal M wave evoked at each bin of the step cycle. In the seated position, locomotor training replaced reciprocal facilitation with reciprocal inhibition in all subjects, and Ib facilitation was replaced by Ib inhibition in 13 out of 14 subjects. During stepping, reciprocal inhibition was decreased at early stance and increased at midswing in American Spinal Injury Association Impairment Scale C (AIS C) and was decreased at midstance and midswing phases in AIS D after training. Ib inhibition was decreased at early swing and increased at late swing in AIS C and was decreased at early stance phase in AIS D after training. The results of this study support that locomotor training alters postsynaptic actions of Ia and Ib inhibitory interneurons on soleus motoneurons at rest and during stepping and that such changes occur in cases with limited or absent supraspinal inputs.

A randomised controlled trial of integrated electrical stimulation and physiotherapy to improve mobility for people less than 6 months post stroke

Purpose: To investigate the feasibility of combining physiotherapy and functional electrical stimulation to improve gait post stroke. Methods: A parallel group partially single-blinded randomised clinical trial. Adults living at home, less than 6 months post stroke, were randomised to Group A (physiotherapy, n = 10) or Group B (physiotherapy and common peroneal nerve stimulation, n = 10). Assessments were conducted before randomisation (Week 1), after intervention (Week 8) and after 12 weeks follow-up (Week 20). Results: No between group differences were observed. There were statistically significant within group differences after the intervention period in both groups for walking speed and distance walked (without stimulation), Rivermead Mobility Index and Canadian Occupational Performance Measure, maintained at Week 20. There was statistically significant improvement in 10-m walking speed (Group B) when the stimulator was used at Week 8 (p = 0.03, median 0.04 m/s (8%)). Only Group B had statistically significant within group change in Rivermead Visual Gait Analysis (Week 8), maintained at Week 20. Conclusions: Integrating electrical stimulation and physiotherapy was feasible and improved walking speed. There was no evidence of a training effect compared with physiotherapy alone. One-hundred forty-four participants per group would produce an adequately powered study based on this protocol.Implications for RehabilitationAt the end of the intervention period participants using electrical stimulation to correct dropped foot walked faster.It was feasible for electrical stimulation to be combined with physiotherapy for people less than 6 months post stroke.A larger adequately powered study is required to establish whether there are training effects associated with use of stimulation in this population.

Long-latency, inhibitory spinal pathway to ankle flexors activated by homonymous group 1 afferents

Inhibitory feedback from sensory pathways is important for controlling movement. Here, we characterize, for the first time, a long-latency, inhibitory spinal pathway to ankle flexors that is activated by low-threshold homonymous afferents. To examine this inhibitory pathway in uninjured, healthy participants, we suppressed motor-evoked potentials (MEPs), produced in the tibialis anterior (TA), by a prior stimulation to the homonymous common peroneal nerve (CPN). The TA MEP was suppressed by a triple-pulse stimulation to the CPN, applied 40, 50, and 60 ms earlier and at intensities of 0.5-0.7 times motor threshold (average suppression of test MEP was 33%). Whereas the triple-pulse stimulation was below M-wave and H-reflex threshold, it produced a long-latency inhibition of background muscle activity, approximately 65-115 ms after the CPN stimulation, a time period that overlapped with the test MEP. However, not all of the MEP suppression could be accounted for by this decrease in background muscle activity. Evoked responses from direct activation of the corticospinal tract, at the level of the brain stem or thoracic spinal cord, were also suppressed by low-threshold CPN stimulation. Our findings suggest that low-threshold muscle and cutaneous afferents from the CPN activate a long-latency, homonymous spinal inhibitory pathway to TA motoneurons. We propose that inhibitory feedback from spinal networks, activated by low-threshold homonymous afferents, helps regulate the activation of flexor motoneurons by the corticospinal tract.

Inter-individual variation in reciprocal Ia inhibition is dependent on the descending volleys delivered from corticospinal neurons to Ia interneurons

IntroductionWe investigated the extent to which the corticospinal inputs delivered to Ia inhibitory interneurons influence the strength of disynaptic reciprocal Ia inhibition. MethodsSeventeen healthy subjects participated in this study. The degree of reciprocal Ia inhibition was determined via short-latency (condition-test interval: 1–3ms) suppression of Sol H-reflex by conditioning stimulation of common peroneal nerve. The effect of corticospinal descending inputs on Ia inhibitory interneurons was assessed by evaluating the conditioning effect of transcranial magnetic stimulation (TMS) on the Sol H-reflex. Then, we determined the relationship between the degree of reciprocal Ia inhibition and the conditioning effect of TMS on the Sol H-reflex. ResultWe found that the degree of reciprocal Ia inhibition and the extent of change in the amplitude of the TMS-conditioned H-reflex, which was measured from short latency facilitation to inhibition, displayed a strong correlation (r=0.76, p<0.01) in the resting conditions. ConclusionThe extent of reciprocal Ia inhibition is affected by the corticospinal descending inputs delivered to Ia inhibitory interneurons, which might explain the inter-individual variations in reciprocal Ia inhibition.

Promoting endogenous associative plasticity in human primary motor cortex

Promoting endogenous associative plasticity in human primary motor cortex

The long-term cost-effectiveness of the use of Functional Electrical Stimulation for the correction of dropped foot due to upper motor neuron lesion

Functional Electrical Stimulation (FES) for correction of dropped foot has been shown to increase mobility, reduce the incidence of falls and to improve quality of life. This study aimed to determine how long the intervention is of benefit, and the total cost of its provision. Retrospective review of medical records. One hundred and twenty-six people with spastic dropped foot (62 stroke, 39 multiple sclerosis, 7 spinal cord injury, 3 cerebral palsy, 15 others) who began treatment in the year 1999. All received common peroneal nerve stimulation, producing dorsiflexion and eversion time to the swing phase of gait using a heel switch. Device usage, 10 m walking speed and Functional Walking Category (FWC) were recorded. The median time of FES use was 3.6 years (mean 4.9, standard deviation 4.1, 95% confidence interval 4.2-5.6) with 33 people still using FES after a mean of 11.1 years. People with stroke walked a mean of 45% faster overall, including a 24% training effect with 52% improving their FWC. People with multiple sclerosis did not receive a consistent training effect but walked 29% faster when FES was used with 40% increasing their FWC. The average treatment cost was £3,095 per patient resulting in a mean cost per Quality Adjusted Life Years of £15,406. FES is a practical, long-term and cost-effective treatment for correction of dropped foot.

Motor Recovery after Spinal Cord Injury Enhanced by Strengthening Corticospinal Synaptic Transmission

The corticospinal tract is an important target for motor recovery after spinal cord injury (SCI) in animals and humans. Voluntary motor output depends on the efficacy of synapses between corticospinal axons and spinal motoneurons, which can be modulated by the precise timing of neuronal spikes. Using noninvasive techniques, we developed tailored protocols for precise timing of the arrival of descending and peripheral volleys at corticospinal-motoneuronal synapses of an intrinsic finger muscle in humans with chronic incomplete SCI. We found that arrival of presynaptic volleys prior to motoneuron discharge enhanced corticospinal transmission and hand voluntary motor output. The reverse order of volley arrival and sham stimulation did not affect or decreased voluntary motor output and electrophysiological outcomes. These findings are the first demonstration that spike timing-dependent plasticity of residual corticospinal-motoneuronal synapses provides a mechanism to improve motor function after SCI. Modulation of residual corticospinal-motoneuronal synapses may present a novel therapeutic target for enhancing voluntary motor output in motor disorders affecting the corticospinal tract.

Neurophysiological characteristics of human leg muscle action potentials evoked by transcutaneous magnetic stimulation of the spine

The objectives of this study were to establish the neurophysiological properties of the compound muscle action potentials (CMAPs) evoked by transcutaneous magnetic stimulation of the spine (tsMSS) and the effects of tsMSS on the soleus H-reflex. In semi-prone seated subjects with trunk semi-flexed, the epicenter of a figure-of-eight magnetic coil was placed at Thoracic 10 with the handle on the midline of the vertebral column. The magnetic stimulator was triggered by monophasic single pulses of 1 ms, and the intensity ranged from 90% to 100% of the stimulator output across subjects. CMAPs were recorded bilaterally from ankle and knee muscles at the interstimulus intervals of 1, 3, 5, 8, and 10 s. The CMAPs evoked were also conditioned by posterior tibial and common peroneal nerve stimulation at a conditioning-test (C-T) interval of 50 ms. The soleus H-reflex was conditioned by tsMSS at the C-T intervals of 50, 20, -20, and -50 ms. The amplitude of the CMAPs was not decreased when evoked at low stimulation frequencies, excitation of group I afferents from mixed peripheral nerves in the leg affected the CMAPs in a non-somatotopical neural organization pattern, and tsMSS depressed soleus H-reflex excitability. These CMAPs are likely due to orthodromic excitation of nerve motor fibers and antidromic depolarization of different types of afferents. The latency of these CMAPs may be utilized to establish the spine-to-muscle conduction time in central and peripheral nervous system disorders in humans. tsMSS may constitute a non-invasive modality to decrease spinal reflex hyperexcitability and treat hypertonia in neurological disorders.

Modulation of reciprocal and presynaptic inhibition during robotic-assisted stepping in humans

ObjectiveTo establish the modulation pattern of reciprocal inhibition and presynaptic inhibition of soleus Ia afferents during robot-assisted stepping in healthy subjects. MethodsDuring stepping, the soleus H-reflex was conditioned by percutaneous stimulation of the ipsilateral common peroneal nerve with a single pulse at stimulation intensities that ranged from 0.9 to 1.2 TA M-wave motor thresholds across subjects. To control for movement of recording and stimulating electrodes, a supramaximal stimulus 80ms after the conditioned and/or unconditioned H-reflexes was delivered to the posterior tibial nerve. The short (2, 3, 4ms) and long (60–80ms) conditioning-test intervals at which the largest amount of reflex depression was observed with the subjects seated were utilized during stepping. Stimuli were randomly dispersed across the step cycle which was divided into 16 equal bins. ResultsReciprocal inhibition exerted from flexor group I afferents onto soleus motoneurons was decreased at mid-stance and increased and late-stance and throughout the swing phase. Presynaptic inhibition of soleus Ia afferents was increased at heel strike and decreased at late-stance and early swing phases. ConclusionReciprocal inhibition between ankle antagonistic muscles and presynaptic inhibition of soleus Ia afferents are modulated in a similar pattern to that reported during walking on a treadmill with full weight bearing and without robot-assisted leg movement. SignificanceThe activity of spinal interneuronal circuits engaged in patterned locomotor activity supports a reciprocal gait pattern during robot-assisted stepping in healthy humans.

Peripheral Magnetic Stimulation to Decrease Spasticity in Cerebral Palsy

Muscle spasticity in pediatric cerebral palsy limits movement and disrupts motor performance, thus its reduction is important in rehabilitation to optimize functional motor development. Our pilot study used repetitive peripheral magnetic stimulation, because this emerging technology influences spinal and cerebral synaptic transmission, and its antispastic effects were reported in adult neurologic populations. We tested whether five sessions of tibial and common peroneal nerve stimulation exerted acute and long-term effects on spasticity of the ankle plantar flexor muscles in five spastic diparetic children (mean age, 8 years and 3 months; standard deviation, 1 year and 10 months). Muscle resistance to fast stretching was measured with a manual dynamometer as a spasticity indicator. A progressive decrease was observed for the more impaired leg, reaching significance at the third session. This sustained reduction of spasticity may reflect that the peripheral stimulation improved the controls over the spinal circuitry. It thus suggests that a massive stimulation-induced recruitment of sensory afferents may be able to influence central nervous system plasticity in pediatric cerebral palsy.

Absence of effects of contralateral group I muscle afferents on presynaptic inhibition of Ia terminals in humans and cats

Crossed effects from group I afferents on reflex excitability and their mechanisms of action are not yet well understood. The current view is that the influence is weak and takes place indirectly via oligosynaptic pathways. We examined possible contralateral effects from group I afferents on presynaptic inhibition of Ia terminals in humans and cats. In resting and seated human subjects the soleus (SO) H-reflex was conditioned by an electrical stimulus to the ipsilateral common peroneal nerve (CPN) to assess the level of presynaptic inhibition (PSI_control). A brief conditioning vibratory stimulus was applied to the triceps surae tendon at the contralateral side (to activate preferentially Ia muscle afferents). The amplitude of the resulting H-reflex response (PSI_conditioned) was compared to the H-reflex under PSI_control, i.e., without the vibration. The interstimulus interval between the brief vibratory stimulus and the electrical shock to the CPN was -60 to 60 ms. The H-reflex conditioned by both stimuli did not differ from that conditioned exclusively by the ipsilateral CPN stimulation. In anesthetized cats, bilateral monosynaptic reflexes (MSRs) in the left and right L(7) ventral roots were recorded simultaneously. Conditioning stimulation applied to the contralateral group I posterior biceps and semitendinosus (PBSt) afferents at different time intervals (0-120 ms) did not have an effect on the ipsilateral gastrocnemius/soleus (GS) MSR. An additional experimental paradigm in the cat using contralateral tendon vibration, similar to that conducted in humans, was also performed. No significant differences between GS-MSRs conditioned by ipsilateral PBSt stimulus alone and those conditioned by both ipsilateral PBSt stimulus and contralateral tendon vibration were detected. The present results strongly suggest an absence of effects from contralateral group I fibers on the presynaptic mechanism of MSR modulation in relaxed humans and anesthetized cats.