Startle stimuli exert opposite effects on human cortical and spinal motor system excitability in leg muscles

Increased excitability of the spinal motor system has been observed after loud and unexpected acoustic stimuli (AS) preceding H-reflexes. The paradigm has been proposed as an electrophysiological marker of reticulospinal tract activity in humans. The brainstem reticular formation also maintains dense anatomical interconnections with the cortical motor system. When a startling AS is delivered, prior to transcranial magnetic stimulation (TMS), the AS produces a suppression of motor evoked potential (MEP) amplitude in hand and arm muscles of healthy subjects. Here we analyzed the conditioning effect of a startling AS on MEP amplitude evoked by TMS to the primary motor leg area. Ten healthy volunteers participated in two experiments that used a conditioning-test paradigm. In the first experiment, a startling AS preceded a suprathreshold transcranial test stimulus. The interstimulus interval (ISI) varied between 20 to 160 ms. When given alone, the test stimulus evoked a MEP amplitude of approximately 0.5 mV in the slightly preinervated soleus muscle (SOL). In the second experiment, the startling AS was used to condition the size of the H-reflex in SOL muscle. Mean MEP amplitude was calculated for each ISI. The conditioning AS suppressed MEP amplitude at ISIs of 30-80 ms. By contrast, H-reflex amplitude was augmented at ISIs of 100-200 ms. In conclusions, acoustic stimulation exerts opposite and ISI-specific effects on the amplitude of MEPs and H-reflex in the SOL muscle, indicating different mechanism of auditory-to-motor interactions at cortical and spinal level of motor system.     

Static otolithic drive alters presynaptic inhibition in soleus motor pool

The vestibular system has both direct and indirect connections to the soleus motor pool via the vestibulospinal and reticulospinal tracts. The exact nature of how this vestibular information is integrated within the spinal cord is largely unknown. The purpose of this study was to identify whether changes in static otolithic drive altered the amount of presynaptic inhibition in the soleus H-reflex pathway. Changes in static otolithic drive were investigated in sixteen healthy participants using a tilt table. Two presynaptic pathways (common peroneal and femoral) to the soleus H-reflex were tested in three weight conditions (supine, non-weight bearing, and weight bearing). The dependent variable was the peak-to-peak amplitude of the soleus H-reflex. Inhibition to the soleus motor pool through the common peroneal nerve pathway differed significantly during weight conditions and tilt. During tilt and non-weight bearing there was greater inhibition of the soleus H-reflex compared to supine, however, this effect was reversed during tilt and weight bearing. Facilitation from the femoral nerve pathway was reduced by tilt compared to supine, but this reduction was unaffected by weight condition. This supports a role of the vestibular system as providing complex, task-dependent presynaptic input to motoneurons in the lower limbs.     

Normal anatomy and physiology of the spinal cord dorsal horn

The dorsal horn of the spinal cord receives afferent input from innocuous primary afferent neurons via collaterals from the dorsal columns. This input is integrated and relayed primarily by neurons in laminae III-VI. Dorsal horn neurons which encode innocuous inputs project to the medulla and the cervical spinal cord via the dorsal columns and the dorsolateral funiculus. Nociceptive primary afferent neurons enter the spinal dorsal horn via collaterals from Lissauer's tract. Nociceptive input is integrated and relayed by neurons in laminae I, II and V which project to the reticular formation and thalamus via the anterolateral tract.     

The influence of vibration on spinal alpha-motoneurons excitability in static conditions and during evoked stepping in human

In healthy human the excitability of spinal alpha-motoneurons under application of vibrostimulation (20-60 Hz) to different leg muscles was investigated both in stationary condition and during stepping movements caused by vibration in the condition of suspended leg. In 15 subjects the amplitude of H-reflex were compared under vibration of rectus femoris (RF) and biceps femoris (BF) muscles of left leg as well during vibration of rectus femoris of contralateral, motionless leg in three spatial positions: upright, supine and on right side of body with suspended left leg. In dynamic conditions the amount of H-reflex was compared during evoked and voluntary stepping at 8 intervals of step cycle. In all body positions the vibration of each ipsilateral leg muscles caused significant suppression of H-reflex, this suppression was more prominent in the air-stepping conditions. The vibration of contralateral leg RF muscle had a weak influence on the amplitude of H-reflex. In 7 subjects the muscle vibration of ipsilateral and contralateral legs generated stepping movements. During evoked "air-stepping" H-reflex had different amplitudes in different phases of step cycle. At the same time the differences between responses under voluntary and non-voluntary stepping were revealed only in stance phase. Thus, different degree of H-reflex suppression by vibration under different body position in space depends on, it seems to be, from summary afferent inflows to spinal cord interneurons, which participate in regulation of posture and locomotion. Seemingly, the increasing of spinal cord neurons excitability occurs under involuntary air-stepping in swing phase, which is necessary for activation of locomotor automatism under unloading leg conditions.     

Growth hormone attenuates alterations in spinal cord evoked potentials and cell injury following trauma to the rat spinal cord

The influence of exogenous rat growth hormone on spinal cord injury induced alterations in spinal cord evoked potentials (SCEP) and edema formation was examined in a rat model. Repeated topical application of rat growth hormone (20microl of 1microg/ml solution) applied 30min before injury and at 0min (at the time of injury), 10min, 30min, 60min, 120min, 180min, and 240min, resulted in a marked preservation of SCEP amplitude after injury. In addition, the treated traumatised cord showed significantly less edema and cell changes. These observations suggest that growth hormone has the capacity to improve spinal cord conduction and attenuate edema formation and cell injury in the cord indicating a potential therapeutic implication of this peptide in spinal cord injuries.     

On the methods employed to record and measure the human soleus H-reflex

The aim of this study was to investigate if the magnitude of the soleus H-reflex is different depending on the method employed to measure its size (peak-to-peak amplitude vs. area). In this study, 13 healthy human subjects participated, while the soleus H-reflex was induced via conventional methods. In the first experiment, the soleus H-reflex was recorded via two monopolar electrodes and was evoked at least at eight different stimulation intensities in respect to the recovery curve of the H-reflex and at three different inter-stimulus intervals (ISIs) (8, 5, and 2 s). The ISI refers to the time delay between the single pulses delivered to the posterior tibial nerve within a single trial. In the second experiment, the effects of common peroneal nerve (CPN) stimulation at short (2-4 ms) and at long (60-120 ms) conditioning test (C-T) intervals on the soleus H-reflex elicited every 5 s were established. Control and conditioned reflexes were recorded via a single differential bipolar electrode. In both experiments, H-reflexes were quantified by measuring their size as peak-to-peak amplitude and as area under the full-wave rectified waveform. The reflex responses recorded through two monopolar electrodes across stimulation intensities and ISIs measured as peak-to-peak amplitude had larger values than measured as area. In contrast, the magnitude of the reflexes, conditioned by CPN stimulation at either short or long C-T intervals and recorded via a single differential electrode, were not significantly different when measured as peak-to-peak amplitude or as area. Our findings indicate that monopolar recordings yield different reflex sizes depending on the method employed to measure the reflex size, and that the H-reflex measured as area might detect better the homosynaptic reflex depression. The lack of observing such differences with bipolar recordings might be related to changes of the reflex shape at a given stimulus intensity due to inhibitory inputs. The implications of our findings are discussed in respect to human reflex studies.     

Evaluation of lumbar enlargement motor neuron excitability: Comparison between H-reflex and transcutaneous spinal cord stimulation

Multisegmental muscle responses (MMR) are reflexes in the leg muscles evoked by transcutaneous electrical spinal cord stimulation over the Th11–Th12 vertebrae. We have used MMR to evaluate the excitability of lumbosacral motor neurons in individuals having paraplegia of low limbs. Ten individuals were tested using H-reflexes and MMR bilaterally before (n ₀ = 20) and during 4-weeks course of rehabilitation (n=76). The H-reflex and MMR of m. gastrocnemius lateralis were obtained in: 15 and 13 cases out of 20, respectively. Both reflexes were recorded in 11 and were absent in 3 cases, matched up to 70% of recordings. In dynamic, the both methods were 100% reproducible and the responses’ amplitude varied in similar directions in 67% of records. The data confirm the validity and reproducibility of the MMR for evaluation of the motor neurons excitability in lumbosacral cord. The H-reflex magnitude shows moderate correlation with MMR in m. gastrocnemius lateralis (r = 0.59, p < 0.001), and weak correlation with MMR in mm. rectus femoris, biceps femoris, and tibialis anterior (r < 0.40, p < 0.001). These findings do not allow extrapolate the results from the H-reflex measurement on the state of lumbosacral cord on the whole. At the same time, measurements of the MMR allow estimate simultaneously the excitability of motor pools innervating several muscle groups. This gives the possibility to assess the functional state of the motor neurons in the lumbosacral cord for clinical and experimental studies, including the spinal cord damage.     

Neural adaptation to resistance training: changes in evoked V-wave and H-reflex responses.

Combined V-wave and Hoffmann (H) reflex measurements were performed during maximal muscle contraction to examine the neural adaptation mechanisms induced by resistance training. The H-reflex can be used to assess the excitability of spinal alpha-motoneurons, while also reflecting transmission efficiency (i.e., presynaptic inhibition) in Ia afferent synapses. Furthermore, the V-wave reflects the overall magnitude of efferent motor output from the alpha-motoneuron pool because of activation from descending central pathways. Fourteen male subjects participated in 14 wk of resistance training that involved heavy weight-lifting exercises for the muscles of the leg. Evoked V-wave, H-reflex, and maximal M-wave (M(max)) responses were recorded before and after training in the soleus muscle during maximal isometric ramp contractions. Maximal isometric, concentric, and eccentric muscle strength was measured by use of isokinetic dynamometry. V-wave amplitude increased approximately 50% with training (P < 0.01) from 3.19 +/- 0.43 to 4.86 +/- 0.43 mV, or from 0.308 +/- 0.048 to 0.478 +/- 0.034 when expressed relative to M(max) (+/- SE). H-reflex amplitude increased approximately 20% (P < 0.05) from 5.37 +/- 0.41 to 6.24 +/- 0.49 mV, or from 0.514 +/- 0.032 to 0.609 +/- 0.025 when normalized to M(max). In contrast, resting H-reflex amplitude remained unchanged with training (0.503 +/- 0.059 vs. 0.499 +/- 0.063). Likewise, no change occurred in M(max) (10.78 +/- 0.86 vs. 10.21 +/- 0.66 mV). Maximal muscle strength increased 23-30% (P < 0.05). In conclusion, increases in evoked V-wave and H-reflex responses were observed during maximal muscle contraction after resistance training. Collectively, the present data suggest that the increase in motoneuronal output induced by resistance training may comprise both supraspinal and spinal adaptation mechanisms (i.e., increased central motor drive, elevated motoneuron excitability, reduced presynaptic inhibition).     

Supersensitivity of the GABA receptor in the frog spinal cord, as induced by kainic acid

In the isolated frog spinal cord perfused with kainic acid (KA, 5 X 10(-4) M) containing Ringer's solution, within 2 hr there were increases in the amplitude of the dorsal root depolarization, as induced by the GABA-agonists. KA perfusion produced increases in the specific binding of [3H]muscimol to crude synaptic membranes and incubation with KA for 3 hr did not increase [3H]muscimol binding. [3H]GABA was released from KA-treated spinal cord slices in the presence of high K+. KA-induced supersensitivity of the dorsal root to GABA may relate to direct actions on primary afferent terminals and not to denervation of GABAergic neurons.     

Control of locomotion in vitro: I. Deafferentation

We previously described the ability to induce adult-like, coordinated airstepping following electrical stimulation of the brainstem in the hindlimb-attached, in vitro brainstem-spinal cord preparation. These findings suggest the presence at birth of supraspinal systems capable of activating and modulating spinal locomotor mechanisms, which presumably also are present at birth. The current study employed the hindlimb-attached in vitro brainstem-spinal cord preparation from 0- to 4-day-old rats maintained in oxygenated artificial cerebrospinal fluid. After the control threshold-frequency relationship for eliciting airstepping was established, the dorsal roots to the attached limbs were severed and the procedure was repeated. No changes in electrical threshold or major differences in the elicited locomotor pattern were observed after deafferentation, although the amplitude of the electromyograms decreased. The mean frequency of alternation at threshold before deafferentation was similar to that after deafferentation. However, the maximum mean frequency induced by suprathreshold stimulation was significantly higher after deafferentation than that before deafferentation. These results suggest that (1) the supraspinal modulation of spinal locomotor mechanisms is not entirely dependent on afferent input; (2) intrinsic spinal locomotor mechanisms are present in the spinal cord at birth; and (3) afferent input may limit the maximum frequency of alternation of the limbs early in development.     

Increased spinal reflex excitability is not associated with neural plasticity underlying the cross-education effect.

The purpose of this study was to examine the effects of a 5-wk unilateral, isometric strength-training program on plasticity in the spinal Hoffmann (H-) reflex in both the trained and untrained legs. Sixteen participants, 22-42 yr old, were assigned to either a control (n = 6) or an exercise group (n = 10). Both groups were tested for plantar flexion maximal voluntary isometric contractions (MVIC) and soleus H-reflex amplitude in both limbs, at the beginning and at the end of a 5-wk interval. Participants in the exercise group showed significantly increased MVIC in both legs after training (P < 0.05), whereas strength was unchanged in the control group for either leg. Subjects in the exercise group displayed increased (P < 0.05) H-reflex amplitudes on the ascending limb of the recruitment curve (at an equivalent M wave of 5% of the maximal M wave, H(A)) only in the trained leg. Maximal H-reflex and M-wave remained unchanged with training. Increased amplitude of H(A) in the trained limb concurrent with increased strength suggests that spinal mechanisms may underlie the changes in strength, possibly because of increased alpha-motoneuronal excitability or reduced presynaptic inhibition. Despite a similar increase in strength in the contralateral limb of the exercise group, H(A) amplitude was unchanged. We conclude that the cross-education effect of strength training may be due to supraspinal to a greater extent than spinal mechanisms.     

Time Course of Immediate Early Gene Protein Expression in the Spinal Cord following Conditioning Stimulation of the Sciatic Nerve in Rats

Long-term potentiation induced by conditioning electrical stimulation of afferent fibers is a widely studied form of synaptic plasticity in the brain and the spinal cord. In the spinal cord dorsal horn, long-term potentiation is induced by a series of high-frequency trains applied to primary afferent fibers. Conditioning stimulation (CS) of sciatic nerve primary afferent fibers also induces expression of immediate early gene proteins in the lumbar spinal cord. However, the time course of immediate early gene expression and the rostral-caudal distribution of expression in the spinal cord have not been systematically studied. Here, we examined the effects of sciatic nerve conditioning stimulation (10 stimulus trains, 0.5 ms stimuli, 7.2 mA, 100 Hz, train duration 2 s, 8 s intervals between trains) on cellular expression of immediate early genes, Arc, c-Fos and Zif268, in anesthetized rats. Immunohistochemical analysis was performed on sagittal sections obtained from Th13- L5 segments of the spinal cord at 1, 2, 3, 6 and 12 h post-CS. Strikingly, all immediate early genes exhibited a monophasic increase in expression with peak increases detected in dorsal horn neurons at 2 hours post-CS. Regional analysis showed peak increases at the location between the L3 and L4 spinal segments. Both Arc, c-Fos and Zif268 remained significantly elevated at 2 hours, followed by a sharp decrease in immediate early gene expression between 2 and 3 hours post-CS. Colocalization analysis performed at 2 hours post-CS showed that all c-Fos and Zif268 neurons were positive for Arc, while 30% and 43% of Arc positive neurons were positive for c-Fos and Zif268, respectively. The present study identifies the spinal cord level and time course of immediate early gene (IEGP) expression of relevance for analysis of IEGPs function in neuronal plasticity and nociception.     

Imbalance in multiple sclerosis: a result of slowed spinal somatosensory conduction

Balance problems and falls are common in people with multiple sclerosis (MS) but their cause and nature are not well understood. It is known that MS affects many areas of the central nervous system that can impact postural responses to maintain balance, including the cerebellum and the spinal cord. Cerebellar balance disorders are associated with normal latencies but reduced scaling of postural responses. We therefore examined the latency and scaling of automatic postural responses, and their relationship to somatosensory evoked potentials (SSEPs), in ten people with MS and imbalance and ten age-, sex-matched, healthy controls. The latency and scaling of postural responses to backward surface translations of five different velocities and amplitudes, and the latency of spinal and supraspinal somatosensory conduction, were examined. Subjects with MS had large, but very delayed automatic postural response latencies compared to controls (161 +/- 31 ms vs. 102 +/- 21 ms, p < 0.01) and these postural response latencies correlated with the latencies of their spinal SSEPs (r = 0.73, p < 0.01). Subjects with MS also had normal or excessive scaling of postural response amplitude to perturbation velocity and amplitude. Longer latency postural responses were associated with less velocity scaling and more amplitude scaling. Balance deficits in people with MS appear to be caused by slowed spinal somatosensory conduction and not by cerebellar involvement. People with MS appear to compensate for their slowed spinal somatosensory conduction by increasing the amplitude scaling and the magnitude of their postural responses.     

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.     

On the methods employed to record and measure the human soleus H-reflex

The aim of this study was to investigate if the magnitude of the soleus H-reflex is different depending on the method employed to measure its size (peak-to-peak amplitude vs. area). In this study, 13 healthy human subjects participated, while the soleus H-reflex was induced via conventional methods. In the first experiment, the soleus H-reflex was recorded via two monopolar electrodes and was evoked at least at eight different stimulation intensities in respect to the recovery curve of the H-reflex and at three different inter-stimulus intervals (ISIs) (8, 5, and 2?s). The ISI refers to the time delay between the single pulses delivered to the posterior tibial nerve within a single trial. In the second experiment, the effects of common peroneal nerve (CPN) stimulation at short (2–4?ms) and at long (60–120?ms) conditioning test (C-T) intervals on the soleus H-reflex elicited every 5?s were established. Control and conditioned reflexes were recorded via a single differential bipolar electrode. In both experiments, H-reflexes were quantified by measuring their size as peak-to-peak amplitude and as area under the full-wave rectified waveform. The reflex responses recorded through two monopolar electrodes across stimulation intensities and ISIs measured as peak-to-peak amplitude had larger values than measured as area. In contrast, the magnitude of the reflexes, conditioned by CPN stimulation at either short or long C-T intervals and recorded via a single differential electrode, were not significantly different when measured as peak-to-peak amplitude or as area. Our findings indicate that monopolar recordings yield different reflex sizes depending on the method employed to measure the reflex size, and that the H-reflex measured as area might detect better the homosynaptic reflex depression. The lack of observing such differences with bipolar recordings might be related to changes of the reflex shape at a given stimulus intensity due to inhibitory inputs. The implications of our findings are discussed in respect to human reflex studies.     

Spinal mechanisms of electric organ discharge synchronization in Gymnotus carapo

Summary The duration of the electric organ discharge (EOD) in Gymnotus carapo is brief and independent of fish size. Spinal mechanisms involved in electrocyte synchronization were explored by recording spontaneous action potentials of single fibers from the electromotor bulbospinal tract (EBST). Using the field potential of the medullary electromotor nucleus (MEN) as a temporal reference we calculated the orthodromic conduction velocity (CV) of these fibers (range: 10.7–91 m/s).The CVs (in m/s) of fibers recorded at the same level of the spinal cord were significantly different in small and large fish; this difference disappeared when CV were expressed as percentage of body length/ms. Plotting these values against conduction distance (also in %) showed that low CV fibers predominate in the rostral cord while only fast fibers are found at distal levels. Moreover, antidromic stimulation of the distal cord was only effective on high CV fibers. The orthodromic CVs in the distal portion of the recorded fibers were calculated by collision experiments; no significant differences were found between proximal and distal portions.The spatial distribution of CV values within the EBST is proposed to play the main role in synchronizing the electromotoneurons' activity along the spinal cord.Abbreviations EOD electric organ discharge - EO electric organ - EBST electromotor bulbospinal tract - MEN medullary electromotor nucleus - CV conduction velocity - EMN electromotoneuron     

正常中国人中枢运动系统传导时间的测定

本文应用高电压、低输出阻抗刺激器,经皮给予大脑皮层和脊髓电刺激(BSPES),同时在上肢鱼际(Thenar)和下肢胫骨前肌(Muscle tibialis anterior)上记录诱发肌肉动作电位,测定了64名正常健康中国人(男:46;女:18)的中枢运动系统传导时间。受试者年龄为20—67岁,身高为156—185cm。刺激大脑皮层出现反应的潜伏期与刺激脊髓出现反应的潜伏期之差为中枢运动传导时间(CMCT)。实验测得鱼际的 CMCT 为6.69±1.48ms;胫骨前肌的 CMCT 为12.90±1.59ms。经统计学处理证明,CMCT 与左右侧肢体、性别、年龄及身高无关。说明 CMCT 是无损伤测定与评价中枢运动系统功能的较精确的一种客观指标。本文根据所测数据,计算出脊髓内运动传导速度为71.34±10.89 m/s,与文献报道的锥体束传导速度50—70 m/s 相近。因此,CMCT 反映了锥体束的传导时间。     

Role of neural afferents from working limbs in exercise hyperpnea

To determine the role of reflex discharge of afferent nerves from the working limbs in the exercise hyperpnea, 1.5- to 2.5-min periods of phasic hindlimb muscle contraction were induced in anesthetized cats by bilateral electrical stimulation of ventral roots L7, S1, and S2. Expired minute ventilation (VE) and end-tidal PCO2 (PETCO2) were computed breath by breath, and mean arterial PCO2 (PaCO2) was determined from discrete blood samples and, also in most animals, by continuous measurement with an indwelling PCO2 electrode. During exercise VE rose progressively with a half time averaging approximately 30 s, but a large abrupt increase in breathing at exercise onset typically did not occur. Mean PaCO2 and PETCO2 remained within approximately 1 Torr of control levels across the work-exercise transition, and PaCO2 was regulated at an isocapnic level after VE had achieved its peak value. Sectioning the spinal cord at L1-L2 did not alter these response characteristics. Thus, reflex discharge of afferent nerves from the exercising limbs was not requisite for the matching of ventilation to metabolic demand during exercise.     

The relationship between the soleus H-reflex amplitude and vibratory inhibition in controls and spastic subjects. II. Computer model

A computer model is presented that describes soleus H-reflex recruitment as a function of electric stimulus intensity. The model consists of two coupled non-linear transfer functions. The first transfer function describes the activation of muscle spindle (Ia) afferent terminals as a function of the electric stimulus intensity; whereas the second describes the activation of a number of motoneurons as a function of the number of active Ia afferent terminals. The effect of change in these transfer functions on the H-reflex recruitment curve is simulated. In spastic patients, a higher average maximal H-response amplitude is observed in combination with a decreased H-reflex threshold. Vibration of the Achilles tendon reduces the H-reflex amplitude, presumably by reducing the excitatory afferent input. Vibratory inhibition is diminished in spasticity. In the model, the afferent-motoneuron transfer function was modified to represent the possible alterations occurring in spasticity. The simulations show that vibratory suppression of the H-reflex is determined only in part by the inhibition level of the afferent input. With a constant level of presynaptic inhibition, the suppression of reflexes of different sizes may vary. A lowering of the motoneuron activation thresholds in spastic patients will directly contribute to a decrease of vibratory inhibition in spasticity.     

Characteristics of the potential of the dorsal surface of the spinal cord in a chronic deficit of afferent influences

The changes of spinal cord dorsal potential (SCDP) has been studied on white rats to the posterior root stimulation at different intervals after sciatic nerve cutting. The increase of threshold, the decrease of amplitude, the growth of duration in some components of SCDP have been revealed on the site of the cutting. These changes were manifested at a less degree on the contralateral cutting site. A conclusion concerning the relative resistance of the spinal cord afferent system to the prolonged absence of peripheral afferent influence has been drawn.