Electromyographic Components Research Articles

Phasic and tonic muscle synergies are different in number, structure and sparseness

In the last two decades, muscle synergies analysis has been commonly used to assess the neurophysiological mechanisms underlying human motor control. Several synergy models and algorithms have been employed for processing the electromyographic (EMG) signal, and it has been shown that the coordination of motor control is characterized by the presence of phasic (movement-related) and tonic (anti-gravity and related to co-contraction) EMG components. Neural substrates indicate that phasic and tonic components have non-homogeneous origin; however, it is still unclear if these components are generated by the same set of synergies or by distinct synergies. This study aims at testing whether phasic and tonic components are generated by distinct phasic and tonic synergies or by the same set of synergies with phasic and tonic activation coefficients. The study also aims at characterizing the differences between the phasic and the tonic synergies. Using a comprehensive mapping of upper-limb point-to-point movements, synergies were extracted from phasic and tonic EMG signal separately, estimating the tonic components with a linear ramp model. The goodness of reconstruction (R2) as a function of the number of synergies was compared, and sets of synergies extracted from each dataset at three R2 threshold levels (0.80, 0.85, 0.90) were retained for further analysis. Then, shared, phasic-specific, and tonic-specific synergies were extracted from the two datasets concatenated. The dimensionality of the synergies shared between the phasic and the tonic datasets was estimated with a bootstrap procedure based on the evaluation of the distribution of principal angles between the subspaces spanned by phasic and tonic synergies due to noise. We found only few shared synergies, indicating that phasic and tonic synergies have in general different structures. To compare consistent differences in synergy composition, shared, phasic-specific, and tonic-specific synergies were clustered separately. Phasic-specific clusters were more numerous than tonic-specific ones, suggesting that they were more differentiated among subjects. The structure of phasic clusters and the higher sparseness indicated that phasic synergies capture specific muscle activation patterns related to the movement while tonic synergies show co-contraction of multiple muscles for joint stabilization and holding postures. These results suggest that in many scenarios phasic and tonic synergies should be extracted separately, especially when performing muscle synergy analysis in patients with abnormal tonic activity and for tuning devices with gravity support.

Электромиографические компоненты, ассоциированные с внутренней речью

Электромиографические компоненты, ассоциированные с внутренней речью

Contribution of Galvanic Vestibular Stimulation for the Diagnosis of HTLV-1-Associated Myelopathy/Tropical Spastic Paraparesis.

Background and PurposeGalvanic vestibular stimulation (GVS) is a low-cost and safe examination for testing the vestibulospinal pathway. Human T-lymphotropic virus 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a slowly progressive disease that affects the vestibulospinal tract early in its course. This study compared the electromyographic (EMG) responses triggered by GVS of asymptomatic HTLV-1-infected subjects and subjects with HAM/TSP.MethodsBipolar galvanic stimuli (400 ms and 2 mA) were applied to the mastoid processes of 39 subjects (n=120 stimulations per subject, with 60 from each lower limb). Both the short latency (SL) and medium latency (ML) components of the EMG response were recorded from the soleus muscles of 13 healthy, HTLV-1-negative adults (56±5 years, mean±SD), and 26 individuals infected with HTLV-1, of whom 13 were asymptomatic (56±8 years) and 13 had HAM/TSP (60±6 years).ResultsThe SL and ML EMG components were 55±4 and 112±10 ms, respectively, in the group of healthy subjects, 61±6 and 112±10 ms and in the HTLV-1-asymptomatic group, and 67±8 and 130±3 ms in the HAM/TSP group (p=0.001). The SL component was delayed in 4/13 (31%) of the examinations in the HTLV-1-asymptomatic group, while the ML component was normal in all of them. In the HAM/TSP group, the most common alteration was the absence of waves.ConclusionsA pattern of abnormal vestibular-evoked EMG responses was found in HTLV-1-neurological disease, ranging from delayed latency among asymptomatic carriers to the absence of a response in HAM/TSP. GVS may contribute to the early diagnosis and monitoring of nontraumatic myelopathies.

How do you use bispectral index effectively for preventing re-awareness during general anesthesia?

Low incidence (0.1-0.4%) [1,2] awareness during intended general anesthesia brings significant postoperative sequelae to the patient, including sleep disturbances, nightmares, daytime anxiety, and even late psychological symptoms [3]. Traditionally, the detection of intraoperative awareness has been conducted by observing patient movement or developments of tachycardia and hypertension. However, these approaches are often hindered by anesthetics and supportive medicines used during general anesthesia and various surgical events. Recently, the Bispectral index (BIS), a mathematically derived electroencephalographic (EEG) derivative [4], has been adopted during general anesthesia to monitor anesthetic depth. By maintaining the BIS between 40 and 60, which is the manufacturer's recommended value for general anesthesia, a reduction of anesthetic requirement and shorter length of stay in PACU can be achieved [5]. However, a large-scale prospective study (n = 967) reveals that the incidence rate for anesthesia awareness is 0.62% of BIS protocol based monitoring during general anesthesia [6]. Therefore, we need to consider which method is desirable to prevent re-awareness during general anesthesia using BIS monitoring. Seol et al. [7], in this issue of the Korean Journal of Anesthesiology, suggests the role of BIS for monitoring intraoperative awareness, although this is not the main theme of the article. In this present study, when the patients were forced back to awareness during general anesthesia with sevoflurane or desflurane, the mean BIS value at the first response to verbal command was about 90. If the BIS value corresponding to the response to verbal command during anesthetic induction closely parallels that at the time of re-awareness during anesthesia, we can use the BIS values of anesthetic induction for monitoring anesthetic awareness. In the study using propofol, the BIS value was between 51 and 85 (median 67) at the point of transition to re-awareness from loss of response to verbal command [8]. In addition, in the course of induction by propofol, the range of BIS when maintaining the response to verbal command was similar to that of re-awareness from loss of consciousness: between 57 and 88 (median about 80) [9]. However, the median BIS value seemed to be higher during re-awareness than during induction. Further research is necessary to determine if the BIS value in the course of induction is an available parameter to detect re-awareness during surgery under general anesthesia. Furthermore, to use BIS effectively, we should also consider the degree of muscle paralysis. It is known that the BIS value reflects not only electroencephalographic (EEG) activity but also electromyographic (EMG) activity of the facial muscles [10]. After administering muscle relaxants without any sedatives, the BIS value dropped to between 9 and 64, accompanied by the decline of EMG activity. Also, these variations of the BIS decline might be dependent on the degree of neuromuscular blockade. In the study by Seol et al. [7], a wake-up test was not conducted until confirming neuromuscular full recovery by a nerve stimulator. For this reason, BIS related to awareness might record a high value at about 90. Paradoxically, the published reports of awareness have increased since 1990, even though there have been remarkable advancements in the field of anesthesiology [3]. Based on the complaints of the patients with unwanted awareness, the universal use of muscle relaxants during surgical procedures may be closely associated with the increasing incidence of awareness. Also, episodes of awareness have been reported most frequently during anesthetic maintenance, when the neuromuscular block is usually sustained for a suitable surgical condition. Muscle paralytic degrees are changeable during maintenance in each patient because of the variable pharmacokinetic and pharmacodynamic characters of muscle relaxants. Therefore, the variable influences of the current EMG component on the BIS value should be considered when interpreting the values. If a neuromuscular block is conducted, the recommended BIS value would not fully guarantee complete hypnosis. According to the article by Avidan et al. [6], anesthesia awareness was reported at an incidence rate of 0.31% when the minimum alveolar concentration (MAC) value of the anesthetics used was maintained between 0.7-1.3. This data was lower than that of the BIS monitoring based anesthesia, although there was no statistical significance. Therefore, in the cases of using muscle relaxants, BIS monitoring along with MAC based anesthetic management might be desirable. In conclusion, considerable care is necessary in the interpretation of the BIS value when muscle relaxants are administered. Henceforth, it may be necessary to investigate the validity of using the BIS value during the induction period for detecting intraoperative re-awareness.

Decoupling of stretch reflex and background muscle activity during anticipatory postural adjustments in humans

We studied the evolution of stretch reflexes in relation to background electromyographic (EMG) activity in the soleus muscle preceding the onset of voluntary arm raise movements. Our objective was to investigate if changes in reflex EMG and muscle activity occur simultaneously and are similarly scaled in amplitude. Ten human subjects stood with each foot on pedals able to exert short dorsiflexor pulses during stance. Subjects were asked to product consistent voluntary arm raise movements to a target upon a visual cue. In (1/4) of trials, no pulse perturbations were given, but in the remaining (3/4)'s of all trials pulses were given randomly during a 600-ms period, from 400 ms before until 200 ms after the onset of the movements. Perturbation trials were sorted into 20-ms bins post hoc, and the amplitude of the reflex EMG component was calculated and compared to the EMG activity obtained when no pulses were given. Results showed that despite exhibiting similar profiles over time, the background EMG consistently inhibited before the reflex EMG did. However, times of reactivation (rebound) were variable across subjects, with background EMG activating before reflex for some subjects and vice versa for others. The minimum values of inhibition, time of inhibition and time of rebound for background and reflex EMG measures did not show significant linear correlations when all subjects' data were considered. These results suggest that reflex and background EMG components of anticipatory postural adjustments evolve differently in time and amplitude. This has implications for the independent control of reflexes and voluntary muscle activity.

Five basic muscle activation patterns account for muscle activity during human locomotion.

An electromyographic (EMG) activity pattern for individual muscles in the gait cycle exhibits a great deal of intersubject, intermuscle and context-dependent variability. Here we examined the issue of common underlying patterns by applying factor analysis to the set of EMG records obtained at different walking speeds and gravitational loads. To this end healthy subjects were asked to walk on a treadmill at speeds of 1, 2, 3 and 5 kmh(-1) as well as when 35-95% of the body weight was supported using a harness. We recorded from 12-16 ipsilateral leg and trunk muscles using both surface and intramuscular recording and determined the average, normalized EMG of each record for 10-15 consecutive step cycles. We identified five basic underlying factors or component waveforms that can account for about 90% of the total waveform variance across different muscles during normal gait. Furthermore, while activation patterns of individual muscles could vary dramatically with speed and gravitational load, both the limb kinematics and the basic EMG components displayed only limited changes. Thus, we found a systematic phase shift of all five factors with speed in the same direction as the shift in the onset of the swing phase. This tendency for the factors to be timed according to the lift-off event supports the idea that the origin of the gait cycle generation is the propulsion rather than heel strike event. The basic invariance of the factors with walking speed and with body weight unloading implies that a few oscillating circuits drive the active muscles to produce the locomotion kinematics. A flexible and dynamic distribution of these basic components to the muscles may result from various descending and proprioceptive signals that depend on the kinematic and kinetic demands of the movements.

Neural control: novel evaluation of stretch reflex sensitivity.

We evaluated the stretch reflex activities of the elbow flexor and extensor muscles considering the relationship between the reflex electromyographic (EMG) responses and their corresponding standardized muscle stretch velocities. Specifically, muscular stretch velocity was estimated by using ultrasonograms. Stretch reflex EMG responses were elicited in the biceps brachii, brachioradialis and triceps brachii with a ramp-and-hold rotation at the elbow joint, which consisted of various angular velocities for the extension- or flexion-direction. The whole muscle stretch velocity induced by each ramp-and-hold rotation was calculated on the basis of fibre length changes associated with the elbow joint angle. A linear regression equation was fitted to the relation between the whole muscle stretch velocity and the reflex EMG responses, and the variables from the equation were used to quantify sensitivity of each reflex EMG component. The reflex EMG responses were increased as the ramp-and-hold rotational velocity increased. There were no significant differences in the recorded magnitudes of reflex EMG responses with equivalent joint rotational velocity between the brachioradialis and the triceps brachii medial head. These muscles showed the highest reflex responses in the flexor and extensor muscles, respectively. To the contrary, the reflex EMG response elicited by the standardized muscle stretches was significantly greater in the extensor muscles, indicating a higher reflex sensitivity. This was because of the lower muscle stretch velocity of the triceps brachii with an equivalent elbow joint rotation. The stretch reflex sensitivity in both the elbow flexor and extensor muscles might be regulated so as to make the reflex responses the same when the equivalent joint rotational velocity is applied to these muscles.

Short- and long-latency reflex responses during different motor tasks in elbow flexor muscles.

Stretch reflex responses in three elbow flexor muscles - the brachioradialis and the short and long heads of the biceps brachii - were studied during different motor tasks. The motor tasks were iso-velocity (8 deg/s) elbow flexion movements in which the muscles performed shortening or lengthening contractions, or were isometric contractions. Care was taken to maintain constant background electromyographic (EMG) activity in the brachoradialis muscle at a 50-deg elbow angle across the tasks by changing the magnitude of the initial load. During each task, mechanical perturbations (duration 170 ms) were applied at pseudorandom intervals when the elbow angle was 50 deg. The magnitude of the perturbation was varied across tasks in order to induce an elbow extension velocity of 80 deg/s over the first 50 ms after the onset of perturbation. The stretch reflex EMG responses in all muscles varied across the three tasks, despite a constant EMG level and similar perturbation-induced angular velocity in the direction of elbow extension. In particular, both the short- and long-latency reflex EMG components were reduced during the lengthening contractions. Further, the task-dependent variations in the early (M2) and the late (M3) components of the long-latency reflex were different, i.e., the magnitude of M3 was considerably enhanced during the shortening task as compared with that of M2. These findings suggest that central modification was responsible for the task-dependent modulation of late EMG responses.

Cerebellar hypermetria: reduction in the early component of the antagonist electromyogram.

Several articles have described the electromyographic (EMG) patterns underlying cerebellar hypermetria. However, the description of the EMG associated with hypermetria is not consistent between studies. It is hypothesized that the reason for this concerns the criteria used to define and describe the antagonist latency. Several studies on neurologically normal individuals have shown that there are two components to the antagonist EMG: an early component and a late component. However, many studies have identified only one component and have not defined whether it was the early or late component. A reanalysis of one published data set that had previously identified only one antagonist component was performed. The reanalysis suggests that hypermetria can be caused by an absence of an early antagonist EMG component, a delayed late component, or both. In addition, a new measure is suggested that allows this hypothesis to be further evaluated.

Effect of the orbital cortex on the neuronal activity of the tegmentum of the midbrain during a feeding reflex in cats.

Chronic experiments on five cats using a model of a conditioned feeding movement reflex were used to study the effect of functional exclusion of the orbital cortex (by anodic polarization with a constant current) on the nature of rearrangements in spike activity in the ventral part of the tegmentum of the midbrain, as well as on the movement component of a conditioned feeding response. Changes in the frequency characteristics, their latent periods, and histogram analyses of spike impulse structure, as compared with increases in the latent period of the conditioned movement response, its duration, and phasicity, demonstrated that the orbital cortex had an activating effect on the responses of ventrotegmental neurons, which correlate with changes in the conditioned movement in this type of feeding behavior. Changes in the conditioned cellular responses were statistically significant only during the start signal (a tone of 600 Hz) before the start of the electromyographic component of the response, i.e., during the preparation and launching period of the movement response.

Functional significance of the early component of the human blink reflex.

The relationship between the size of the first electromyographic (EMG) component of the cutaneous blink reflex (R1) and onset of eyelid closure in human adults was determined in 4 experiments in which R1 size was varied by different means: change in stimulus intensity, paired stimulation, and warning. Two-phase lid movements were frequently seen, with an early small movement followed by a large rapid movement. All experiments showed that larger R1s were associated with shorter latencies of both movements. This covariation was general across participants and was independent of shifts in the excitability of the blink reflex pathways indexed by R1 latency, R2 latency, and R2 area (R2 is the more prolonged, later EMG component). The results indicate that R1 acts first to evoke an early lid movement and second to facilitate eyelid closure by the later R2 burst. Identification of this second behavioral function for R1 aids the interpretation of other findings and encourages its use as a model system.

EMG activities of mono- and bi-articular muscles during goal-directed ballistic movement

Eight subjects, who were seated with the upper arm supported in a horizontal position, performed a series of elbow flexion and extension movements in which a visual target was provided together with an elbow angle signal by vertically moving horizontal lines on an oscilloscope. Five loading conditions were employed, which differed in the number of steel plates attached to the subject's wrist: 0, 0.65, 1.30, 1.95 and 2.60 kg. The electromyographic (EMG) activity of the bi-articular biceps brachii (BB) was compared with the mono-articular brachioradialis (BR) for each of three EMG components; the first and the second agonist burst (AG1, AG2) during flexion movements, and the antagonist burst (ANT) during extension movements. The magnitude relations for each EMG component between the two muscles were evaluated by the BR/BB ratio. The results showed that there were significant differences ( p < 0.05) among the three EMG components in all but the no-loading condition. Further a post-hoc test revealed that there were significant BR/BB differences ( p < 0.05) between AG1 vs. AG2 in 0.65 and 1.3 kg loading conditions and between AG1 vs. ANT in all but the no-loading condition. These results may suggest that different neural processes underlie the activation of mono- and bi-articular muscles in the organization and the control of movements.

Facilitation and inhibition of the human startle blink reflexes by stimulus anticipation.

The cutaneous eyeblink has 2 electromyographic components, 1 unilateral and early (R1) and 1 bilateral and late (R2), which are served by different neural pathways. These 2 reactions were measured when the eliciting stimulus was expected or relatively surprising. Forewarning was varied in 3 ways: Subjects received notice that the stimulus was about to occur on some trials (Experiment 1); delivered the stimulus to themselves on some trials (Experiments 2 & 3); or experienced a series of trials in which a tone was paired with the eliciting stimulus, followed by tone-alone trials interspersed with test trials (Experiment 4). In each case, forewarning enhanced R1 amplitudes while depressing R2 but reduced the latency of both components. This mixed pattern of effects reveals that the preparatory state provoked by forewarning focuses excitatory and inhibitory processes simultaneously on different reflex pathways: inhibition central and excitation peripheral.

Tibialis anterior response to sudden ankle displacements in normal and parkinsonian subjects

It is well known that in Parkinsonian subjects with akinesia, reaction times are increased but reflex latencies remain normal. We have attempted to use this knowledge to distinguish between ‘reflex’ and ‘voluntary’ components of the electromyographic (EMG) response to ankle displacement. The EMG and torque responses of tibialis anterior (TA) to randomly applied servo-controlled plantar-flexing displacements of the ankle with and without the subject's intentional opposition were examined in 9 Parkinsonian and 9 age-matched normal humans. To obtain a measure of akinesia, the response latency to a visual stimulus was subsequently measured in the same subjects. Three principal findings emerged. (1) The intermediate latency EMG component (PSR) of the response evoked by ankle displacement with the subject instructed to relax was more regularly evoked and of lower threshold in Parkinsonians than in normals. This finding corresponds to the enlarged M2 component in upper limb muscles. However, the facilitation of PSR was not found to be associated with an increase in torque. In fact, the patients did not exhibit more stiffness than normals under our experimental conditions. (2) Mean latency estimate of the PSR was indistinguishable between Parkinsonians and normals. This finding puts the PSR in the nature of a reflex. Indeed, in accordance with reflex behaviour which is proportional to input characteristics, its area increased linearly with increase in the magnitude of displacement velocity. (3) In contrast, the ‘late’ EMG response (FSR) evoked by opposing sudden ankle displacement exhibited a significantly longer latency in 6 out of 8 Parkinsonians than normals. In the same patients, the EMG response latency to a visual signal was similarly increased. The delay of FSR in akinesia patients thus argued against its being a stereotyped reflex. The result is discussed with reference to the recent finding that preprogrammed responses are delayed in Parkinsonians.