Short-term plasticity of spinal reflex excitability induced by rhythmic arm movement

Rhythmic arm movement reduces Hoffmann (H)-reflex amplitudes in leg muscles by modulation of presynaptic inhibition in group Ia transmission. To date only the acute effect occurring during arm movement has been studied. We hypothesized that the excitability of soleus H-reflexes would remain suppressed beyond a period of arm cycling conditioning. Subjects used a customized arm ergometer to perform rhythmic 1-Hz arm cycling for 30 min. H-reflexes were evoked before, during, and after arm cycling via stimulation of the tibial nerve in the popliteal fossa. The most important finding was that the H-reflex amplitudes were significantly suppressed during and 相似文献   

Modulation of human cutaneous reflexes during rhythmic cyclical arm movement

The organization and pattern of cutaneous reflex modulation is unknown during rhythmic cyclical movements of the human upper limbs. On the assumption that these cyclic arm movements are central pattern generator (CPG) driven as has been suggested for leg movements such as walking, we hypothesized that cutaneous reflex amplitude would be independent of electromyographic (EMG) muscle activation level during rhythmic arm movement (phase-dependent modulation, as is often the case in the lower limb during locomotion). EMG was recorded from eight muscles crossing the human shoulder, elbow, and wrist joints while whole arm rhythmic cyclical movements were performed. Cutaneous reflexes were evoked with trains of electrical stimulation delivered at non-noxious intensities (approximately 2 x threshold for radiating paresthesia) to the superficial radial nerve innervating the lateral portion of the back of the hand. Phasic bursts of rhythmic muscle activity occurred throughout the movement cycle. Rhythmic EMG and kinematic patterns were similar to what has been seen in the human lower limb during locomotor activities such as cycling or walking: there were extensive periods of reciprocal activation of antagonist muscles. For most muscles, cutaneous reflexes were modulated with the movement cycle and were strongly correlated with the movement-related background EMG amplitude. It is concluded that cutaneous reflexes are primarily modulated by the background muscle activity during rhythmic human upper limb movements, with only some muscles showing phase-dependent modulation.     

Neural regulation of rhythmic arm and leg movement is conserved across human locomotor tasks

It has been proposed that different forms of rhythmic human limb movement have a common central neural control ('common core hypothesis'), just as in other animals. We compared the modulation patterns of background EMG and cutaneous reflexes during walking, arm and leg cycling, and arm-assisted recumbent stepping. We hypothesized that patterns of EMG and reflex modulation during cycling and stepping (deduced from mathematical principal components analysis) would be comparable to those during walking because they rely on similar neural substrates. Differences between the tasks were assessed by evoking cutaneous reflexes via stimulation of nerves in the foot and hand in separate trials. The EMG was recorded from flexor and extensor muscles of the arms and legs. Angular positions of the hip, knee and elbow joints were also recorded. Factor analysis revealed that across the three tasks, four principal components explained more than 93% of the variance in the background EMG and middle-latency reflex amplitude. Phase modulation of reflex amplitude was observed in most muscles across all tasks, suggesting activity in similar control networks. Significant correlations between EMG level and reflex amplitude were frequently observed only during static voluntary muscle activation and not during rhythmic movement. Results from a control experiment showed that strong correlation between EMG and reflex amplitudes was observed during discrete, voluntary leg extension but not during walking. There were task-dependent differences in reflex modulation between the three tasks which probably arise owing to specific constraints during each task. Overall, the results show strong correlation across tasks and support common neural patterning as the regulator of arm and leg movement during various rhythmic human movements.     

Corticospinal excitability in human subjects during nonrapid eye movement sleep: single and paired-pulse transcranial magnetic stimulation study

The mechanisms responsible for changes in brain function during normal sleep are poorly understood. In this study, we aimed to investigate the effects of sleep on human corticospinal excitability by estimating resting motor threshold (RMT), and latency and amplitude of motor-evoked potentials (MEPs) after delivering transcranial magnetic stimulation (TMS) in ten healthy subjects. We also aimed to study short-interval intracortical inhibition (SICI) during sleep with paired-pulse TMS (pp-TMS). Ten healthy volunteers were studied. They were monitored immediately before, during and after a 3-h sleep (from 1 p.m. to 4 p.m., immediately after the mid-day meal). EEG was continuously recorded during sleep and the various sleep stages were identified off line. Every 10 min, subjects received ten single stimuli (to estimate RMT, MEP latency and amplitude) and six paired stimuli (to estimate SICI). MEP amplitude decreased and latency and RMT increased during the various sleep stages and returned to baseline values on awakening. Post hoc comparisons showed a significant difference in pp-TMS MEP amplitudes between the sleep and all the other conditions. The changes in TMS evoked variables during the different sleep stages indicate that during nonrapid eye movement sleep, cortical pyramidal neuron excitability (as measured by RMT, MEP latency and amplitude) progressively diminishes and the efficiency of the intracortical GABA-ergic network (as assessed by three pp-TMS) increases. On awakening, these sleep-induced changes in corticospinal excitability return rapidly to values observed during wakefulness.     

Feedforward contraction of transversus abdominis is not influenced by the direction of arm movement

 Because the structure of the spine is inherently unstable, muscle activation is essential for the maintenance of trunk posture and intervertebral control when the limbs are moved. To investigate how the central nervous system deals with this situation the temporal components of the response of the muscles of the trunk were evaluated during rapid limb movement performed in response to a visual stimulus. Fine-wire electromyography (EMG) electrodes were inserted into transversus abdominis (TrA), obliquus internus abdominis (OI) and obliquus externus abdominis (OE) of 15 subjects under the guidance of real-time ultrasound imaging. Surface electrodes were placed over rectus abdominis (RA), lumbar multifidus (MF) and the three parts of deltoid. In a standing position, ten repetitions of shoulder flexion, abduction and extension were performed by the subjects as fast as possible in response to a visual stimulus. The onset of TrA EMG occurred in advance of deltoid irrespective of the movement direction. The time to onset of EMG activity of OI, OE, RA and MF varied with the movement direction, being activated earliest when the prime action of the muscle opposed the reactive forces associated with the specific limb movement. It is postulated that the non-direction-specific contraction of TrA may be related to the control of trunk stability independent of the requirement for direction-specific control of the centre of gravity in relation to the base of support. Received: 29 September 1995 / Accepted: 30 September 1996     

Corticospinal excitability during preparation for an anticipatory action is modulated by the availability of visual information

To intercept rapidly moving objects, people must predict the right time to initiate their actions. The timing of movement initiation in interceptions is thought to be determined when a perceptual variable specifying time to contact reaches a criterion value. If a response needs to be aborted, the performer must make a decision before this moment. It has been recently shown that the minimal time to suppress an anticipatory action takes longer during motion extrapolation than during continuous visual information. In experiment 1, we sought to determine whether or not the availability of visual information would 1) affect the latency to inhibit an anticipatory action, and 2) modulate the level of excitability in the motor cortex (M1). The behavioral results showed that the absence of visual information prolonged the latency to stop the movement as previously reported. The neurophysiological data indicated that corticospinal excitability levels were affected by the availability of visual information. In experiment 2, we sought to verify whether corticospinal excitability levels would also differ between the two visual conditions when the task did not involve response suppression. The results of experiment 2 indicated that excitability levels did not differ between visual conditions. Overall, our findings indicated that the buildup of motor activation can also play a role in determining different latencies to inhibit an anticipatory action. They also suggest that the buildup of motor activation in the corticospinal pathways can be strategically modulated to the requirements of the task during continuous visual information.     

Recruitment gain of antagonistic motoneurons is higher during lengthening contraction than during shortening contraction in man

The purpose of this study was to investigate how the recruitment gain, as derived from the Hoffmann (H)-reflex measurement, of antagonistic motoneurons is modulated during voluntary lengthening (LEN) and shortening (SHO) contractions in the human tibialis anterior (TA) muscle. To this end, the parameters of the ratios of the slope in each ascending part of the H and M recruitment curves (Hslp/Mslp) in the antagonist muscle were compared between LEN and SHO contractions in nine young, healthy subjects. Although there were no differences in the levels of background activity (BGA) between LEN and SHO contractions in the agonist (TA) and antagonist (soleus) muscles, the Hslp/Mslp of the antagonist muscle was significantly higher during LEN contractions than during SHO contractions (P<0.01). It was therefore demonstrated that the recruitment gain of the antagonistic motoneurons to the la afferent inputs was higher during LEN contractions than during SHO contractions despite similar BGA levels. This result might reflect differences in the extent of the reciprocal inhibition from the agonist to the antagonist muscles and/or in the neural mechanism underlying the length-changing manners of the antagonist muscle itself.     

Corticospinal excitability is specifically modulated by the social dimension of observed actions

A large body of research reports that perceiving body movements of other people activates motor representations in the observer's brain. This automatic resonance mechanism appears to be imitative in nature. However, action observation does not inevitably lead to symmetrical motor facilitation: mirroring the observed movement might be disadvantageous for successfully performing joint actions. In two experiments, we used transcranial magnetic stimulation (TMS) to investigate whether the excitability of the corticospinal system was selectively modulated by the social dimension of an observed action. We recorded motor-evoked potentials (MEPs) from right-hand muscles during the observation of an action sequence which, depending on context, might or might not elicit a complementary response. The results demonstrate a differential motor facilitation depending on action context. Specifically, when the context called for a complementary action, the excitability pattern reflected the under-threshold activation of a complementary action, whereas when the context did not imply acting in a complementary manner, the observer's corticospinal activity reflected symmetrical motor resonance. We contend that the mechanisms underlying action observation are flexible and respond to contextual factors that guide the social interaction between individuals beyond emulation.     

Rhythmic arm movement is not discrete

Rhythmic movements, such as walking, chewing or scratching, are phylogenetically old motor behaviors found in many organisms, ranging from insects to primates. In contrast, discrete movements, such as reaching, grasping or kicking, are behaviors that have reached sophistication primarily in younger species, particularly primates. Neurophysiological and computational research on arm motor control has focused almost exclusively on discrete movements, essentially assuming similar neural circuitry for rhythmic tasks. In contrast, many behavioral studies have focused on rhythmic models, subsuming discrete movement as a special case. Here, using a human functional neuroimaging experiment, we show that in addition to areas activated in rhythmic movement, discrete movement involves several higher cortical planning areas, even when both movement conditions are confined to the same single wrist joint. These results provide neuroscientific evidence that rhythmic arm movement cannot be part of a more general discrete movement system and may require separate neurophysiological and theoretical treatment.     

Alterations in smooth muscle contraction kinetics during tonic activation

The kinetics of actin myosin interaction were studied in rat tracheal smooth muscle by analyzing the time course of post-vibration tension recovery. Longitudinal vibration (100 Hz sinus; 8% of the muscle length) of the contracted preparation (electrical field stimulation 30 Hz, 0.3 ms or 0.1 mM acetylcholine treatment) inhibits the process of force generation. The tension recovery after cessation of vibration follows a double exponential function with an initial fast and a subsequent slow component (the time constants averaged 1.17±0.10 s and 7.0±0.32 s (n=60), respectively). Changes in the amplitude of vibration, the stimulation strength, or the extent of resting tension affect the amplitude without altering the time constants of tension recovery. These experimental conditions influence rather the number than the kinetics of acting cross-bridges. An extension of the pre-vibration stimulation period from 15s to 16 min as well as a reduction in temperature from 37°C to 25°C hardly affects the extent of force development. However, the time constants of both the fast and the slow component of tension recovery were increased by up to a factor of about 7. These experimental results indicate an effect on the kinetics of actin myosin interaction.     

Heart rate is lower during ergometer rowing than during treadmill running

This study evaluated whether the heart rate (HR) response to exercise depends on body position and on the active muscle mass. The HR response to ergometer rowing (sitting and using both arms and legs) was compared to treadmill running (upright exercise involving mainly the legs) using a progressive exercise intensity protocol in 55 healthy men [mean (SD) height 176 (5) cm, body mass 71 (6) kg, age 21 (3) years]. During rowing HR was lower than during running at a blood lactate concentration of 2 mmol·l^–1 [145 (13) compared to 150 (11) beat·min^–1, P<0.05], 4 mmol·l^–1 [170 (10) compared to 177 (13) beat·min^–1, P<0.05], and 6 mmol·l^–1 [182 (10) compared to 188 (10) beat·min^–1, P<0.05]. Also during maximal intensity rowing, HR was lower than during maximal intensity running [194 (9) compared to 198 (11) beat·min^–1, P<0.05]. These results were accompanied by a higher maximal oxygen uptake during rowing than during running [rowing compared to running, 4.50 (0.5) and 4.35 (0.4) l·min^–1, respectively, P<0.01]. Thus, the oxygen pulse, as an index of the stroke volume of the heart, was higher during rowing than during running at any given intensity. The results suggest that compared to running, the seated position and/or the involvement of more muscles during rowing facilitate venous return and elicit a smaller HR response for the same relative exercise intensity. Electronic Publication     

Neural compensation for compliant loads during rhythmic movement

An experiment was performed to characterise the movement kinematics and the electromyogram (EMG) during rhythmic voluntary flexion and extension of the wrist against different compliant (elastic-viscous-inertial) loads. Three levels of each type of load, and an unloaded condition, were employed. The movements were paced at a frequency of 1 Hz by an auditory metronome, and visual feedback of wrist displacement in relation to a target amplitude of 100 degree was provided. Electromyographic recordings were obtained from flexor carpi radialis (FCR) and extensor carpi radialis brevis (ECR). The movement profiles generated in the ten experimental conditions were indistinguishable, indicating that the CNS was able to compensate completely for the imposed changes in the task dynamics. When the level of viscous load was elevated, this compensation took the form of an increase in the rate of initial rise of the flexor and the extensor EMG burst. In response to increases in inertial load, the flexor and extensor EMG bursts commenced and terminated earlier in the movement cycle, and tended to be of greater duration. When the movements were performed in opposition to an elastic load, both the onset and offset of EMG activity occurred later than in the unloaded condition. There was also a net reduction in extensor burst duration with increases in elastic load, and an increase in the rate of initial rise of the extensor burst. Less pronounced alterations in the rate of initial rise of the flexor EMG burst were also observed. In all instances, increases in the magnitude of the external load led to elevations in the overall level of muscle activation. These data reveal that the elements of the central command that are modified in response to the imposition of a compliant load are contingent, not only upon the magnitude, but also upon the character of the load.     

基于快速节律性运动的皮层脑电分析

节律运动是人们生活中一种基本的运动形式,与单次运动相区别,快速节律运动在脑电中有特殊的表现形式.本文以两位植入皮层电极的癫痫病人作为受试,在1Hz与2Hz听觉节拍器提示下进行手指节律运动,同时记录皮层脑电数据.对脑电数据的能量和相关性进行离线分析,结果显示节律运动中运动感觉皮层脑电的能量在特定频段上呈下降趋势,相干性呈上升趋势,且运动相关能量与相干性在不同的运动速度下具有明显的统计性差异.对不同功能区之间相干性的分析表明辅助运动区可能是与运动速度有关的皮层功能区.     

Corticospinal excitability during painful self-stimulation in humans: a transcranial magnetic stimulation study

We investigated changes in the corticospinal pattern of activity in healthy volunteers during sustained noxious and non-noxious mechanical stimulation of the first hand digit, resulting from active (self-stimulation) or passive (externally-induced) pressing against a sharp or blunted tip. The results indicate that, in order to press a finger onto a noxious stimulus with the same force generated to press onto a non-noxious one, the motor cortex adopts a peculiar strategy in terms of recruitment of motor units. This is reflected by an increase of corticospinal excitability (as revealed by motor potentials evoked by transcranial magnetic stimulation of the contralateral primary motor cortex) and EMG activity of agonist muscles, possibly related to an increase of motor unit synchronization.     

Facilitation of soleus H-reflex amplitude evoked by cutaneous nerve stimulation at the wrist is not suppressed by rhythmic arm movement

Neural connections between the cervical and lumbosacral spinal cord may assist in arm and leg coordination during locomotion. Currently the extent to which arm activity can modulate reflex excitability of leg muscles is not fully understood. We showed recently that rhythmic arm movement significantly suppresses soleus H-reflex amplitude probably via modification of presynaptic inhibition of the IA afferent pathway. Further, during walking reflexes evoked in leg muscles by stimulation of a cutaneous nerve at the wrist (superficial radial nerve; SR) are phase and task dependent. However, during walking both the arms and legs are rhythmically active thus it is difficult to identify the locus of such modulation. Here we examined the influence of SR nerve stimulation on transmission through the soleus H-reflex pathway in the leg during static contractions and during rhythmic arm movements. Nerve stimulation was delivered with the right shoulder in flexion or extension. H-reflexes were evoked alone (unconditioned) or with cutaneous conditioning via stimulation of the SR nerve (also delivered alone without H-reflex in separate trials). SR nerve stimulation significantly facilitated H-reflex amplitude during static contractions with the arm extended and countered the suppression of reflex amplitude induced by arm cycling. The results demonstrate that cutaneous feedback from the hand on to the soleus H-reflex pathway in the legs is not suppressed during rhythmic arm movement. This contrasts with the observation that rhythmic arm movement suppresses facilitation of soleus H-reflex when cutaneous nerves innervating the leg are stimulated. In conjunction with other data taken during walking, this suggests that the modulation of transmission through pathways from the SR nerve to the lumbosacral spinal cord is partly determined by rhythmic activity of both the arms and legs.     

Corticospinal excitability during action observation in task-specific dystonia: a transcranial magnetic stimulation study

Observation of actions performed by other individuals activates the onlooker's motor system in a way similar to real movement execution. The functioning of this mechanism in the pathological domain is not clear yet. The aim of this study was to explore whether action observation activates the motor system of patients affected by a task-specific form of dystonia, such as writer's cramp. Transcranial magnetic stimulation was applied over the primary motor cortex and motor evoked potentials were recorded from hand (FDI and ADM) and forearm (FCR) muscles at baseline and during observation of actions (grasping and writing) or images. Writing actions could be performed with healthy or dystonic movement patterns. Results showed a highly specific and reversed pattern of activation in the FDI muscle of the two groups. Differences between the two writing conditions were significantly opposite in the two groups: control subjects had higher activation during observation of the dystonic compared to the healthy action, whereas in patients observation of the healthy writing led to higher activation than the dystonic writing. This opposite corticospinal modulation might be explained by a different self-attribution of the observed actions in the two groups.     

Interleukin-6 release is higher across arm than leg muscles during whole-body exercise

Exercising muscle releases interleukin-6 (IL-6), but the mechanisms controlling this process are poorly understood. This study was performed to test the hypothesis that the IL-6 release differs in arm and leg muscle during whole-body exercise, owing to differences in muscle metabolism. Sixteen subjects (10 men and six women, with body mass index 24 ± 1 kg m(-2) and peak oxygen uptake 3.4 ± 0.6 l min(-1)) performed a 90 min combined arm and leg cycle exercise at 60% of maximal oxygen uptake. The subjects arrived at the laboratory having fasted overnight, and catheters were placed in the femoral artery and vein and in the subclavian vein. During exercise, arterial and venous limb blood was sampled and arm and leg blood flow were measured by thermodilution. Lean limb mass was measured by dual-energy X-ray absorbtiometry scanning. Before and after exercise, biopsies were obtained from vastus lateralis and deltoideus. During exercise, IL-6 release was similar between men and women and higher (P < 0.05) from arms than legs (1.01 ± 0.42 and 0.33 ± 0.12 ng min(-1) (kg lean limb mass)(-1), respectively). Blood flow (425 ± 36 and 554 ± 35 ml min(-1) (kg lean limb mass)(-1)) and fatty acid uptake (26 ± 7 and 47 ± 7 μmol min(-1) (kg lean limb mass)(-1)) were lower, glucose uptake similar (51 ± 12 and 41 ± 8 mmol min(-1) (kg lean limb mass)(-1)) and lactate release higher (82 ± 32 and -2 ± 12 μmol min(-1) (kg lean limb mass)(-1)) in arms than legs, respectively, during exercise (P < 0.05). No correlations were present between IL-6 release and exogenous substrate uptakes. Muscle glycogen was similar in arms and legs before exercise (388 ± 22 and 428 ± 25 mmol (kg dry weight)(-1)), but after exercise it was only significantly lower in the leg (219 ± 29 mmol (kg dry weight)(-1)). The novel finding of a markedly higher IL-6 release from the exercising arm compared with the leg during whole-body exercise was not directly correlated to release or uptake of exogenous substrate, nor to muscle glycogen utilization.