5-Hydroxytryptamine involvement in the intrinsic control of oesophageal EMG activity

The effects and the sites of action of 5-Hydroxytryptamine (5HT) were examined in transverse muscular strips of pigeon oesophagus. 5-Hydroxytryptamine (0.001 to 30 microM) induced a concentration-dependent excitatory effect on the EMG activity. This response was mainly characterized by an increase in burst frequency. The maximum 5-HT-induced excitatory effect was not altered by methysergide (10 microM), but was abolished by tetrodotoxin (3 microM). Excitatory response to 5-HT was partly opposed by atropine (1 microM), potentiated by 5-methoxy-N, N-dimethyltryptamine (1 microM) and was not altered by guanethidine (10 microM). These results indicate that 5-HT activates the pigeon oesophagus indirectly via neural elements and has no direct action on the smooth muscle cells. 5-HT is thought to stimulate three different intramural neuron types: excitatory cholinergic neurons, excitatory non-cholinergic neurons and inhibitory non-cholinergic non-adrenergic neurons. The action on these different neurons seems to be mediated via different receptors.     

Inhibitory influences of vagal afferences on the oesophageal EMG peristaltic pattern

The influence of vagal afferents on the EMG peristaltic pattern was studied in pigeon oesophagus. Bilateral vagotomy did not abolish the primary peristalsis, but induced significant modifications of the peristaltic pattern parameters. Vagal afferent stimulation induced an inhibitory effect consisting of a temporary break or definitive block of the EMG peristaltic activity already in progress. Vagal afferent stimulation also induced a reduction of the spontaneous EMG activity and this effect was abolished either by glossopharyngeal bilateral section or ganglionic block. Likewise vagal afferent stimulation, the crop distension caused inhibitory effects on EMG peristaltic pattern. This effect was abolished by bilateral vagotomy. These results indicate that vagal afferents, originating from the crop, could influence the central neurons responsible for the peristaltic motor programme.     

Sensory collaterals, intramural ganglia and motor nerves in the guinea-pig bladder: evidence for intramural neural circuits

The afferent output from the bladder is important for triggering micturition. This study identifies different types of afferent nerve and explores the connections of their collateral fibres on intramural ganglia and potential ganglionic targets. The experiments were performed on tissues from male guinea-pigs (n=16). Fibres positive for choline acetyl transferase (ChAT⁺) were found to originate close to the urothelium, to transit the sub-urothelial interstitial cell layer and to pass into the lamina propria. A different population of fibres, immunopositive for calcitonin gene-related peptide (CGRP), capsaicin receptors or neurofilament protein (NF), were seen to intertwine with the ChAT⁺ fibres in the lamina propria. The ChAT⁺ fibres did not express NF. Ganglia with ChAT⁺ and NF⁺ neurones were found in the lamina propria and muscle. ChAT⁺ fibres, with pronounced terminal varicosities, were present on the nerve cell bodies. Two types were noted: NF⁺ terminals and those with little or no NF (NF⁻) suggesting that their origins were the ChAT⁺ afferent collaterals and the adjacent ganglia. Fibres containing CGRP or substance P were seen on the ganglionic cells. α1B adrenergic receptors were also found on the neurones indicative of adrenergic synapses. Thus, the ganglia had multiple inputs. Different types of ChAT⁺ nerves were seen in the muscle: NF⁺ and NF⁻. The ChAT⁺/NF⁺ nerves may represent a ganglionic output to the muscle. This complex neuronal network may therefore represent the elements generating and modulating bladder sensations. The role of such a scheme in bladder pathology and the therapeutic sites of action of anticholinergic and sympathomimetic drugs are discussed.We gratefully acknowledge the support of Pfizer. This work was supported by a grant from the Detrol Research Programme.     

Discovering sparse control strategies in neural activity

Biological circuits such as neural or gene regulation networks use internal states to map sensory input to an adaptive repertoire of behavior. Characterizing this mapping is a major challenge for systems biology. Though experiments that probe internal states are developing rapidly, organismal complexity presents a fundamental obstacle given the many possible ways internal states could map to behavior. Using C. elegans as an example, we propose a protocol for systematic perturbation of neural states that limits experimental complexity and could eventually help characterize collective aspects of the neural-behavioral map. We consider experimentally motivated small perturbations—ones that are most likely to preserve natural dynamics and are closer to internal control mechanisms—to neural states and their impact on collective neural activity. Then, we connect such perturbations to the local information geometry of collective statistics, which can be fully characterized using pairwise perturbations. Applying the protocol to a minimal model of C. elegans neural activity, we find that collective neural statistics are most sensitive to a few principal perturbative modes. Dominant eigenvalues decay initially as a power law, unveiling a hierarchy that arises from variation in individual neural activity and pairwise interactions. Highest-ranking modes tend to be dominated by a few, “pivotal” neurons that account for most of the system’s sensitivity, suggesting a sparse mechanism of collective control.     

Cross-correlation analysis of thalamic neurons and EMG activity in parkinsonian tremor

Bursting activity in cells cross-correlated with electromyographic (EMG) activity during parkinsonian tremor. Statistically significant evidence of cross-correlation was found for 49% of cells located at the lesion target for relief of tremor. Statistically significant correlation was found for 90% of cells having tremor frequency power greater than twice 'average power' at nontremor frequencies. This population of cells may be involved in the generation of parkinsonian tremor.     

Electrical stimulation of glossopharyngeal nerve and oesophageal EMG response in the pigeon

The effects of the efferent glossopharyngeal nerve stimulation, on EMG activity of the pigeon cervical oesophagus, were studied. In control animals, stimulation caused a biphasic response characterized by an intra-stimulus excitatory component followed by a post-stimulus inhibitory one. The EMG response to glossopharyngeal stimulation appeared simultaneously throughout the cervical oesophagus. A bell-shaped mechanical wave was detected relating to the electrical excitatory component. Atropine administration antagonized the excitatory component, while the inhibitory one persisted. It occurs intra-stimulus, and its duration is increased, compared to control ones. A reduction in the oesophageal resting pressure was observed relating to the electrical inhibitory component. Hexamethonium caused complete disappearance of any EMG response to glossopharyngeal stimulation, as well as suppression of mechanical responses. The comparison between the EMG responses to swallow and to efferent glossopharyngeal stimulation suggests that in pigeon cervical oesophagus: primary peristalsis is central in origin; a dual system of glossopharyngeal fibres, excitatory and inhibitory, carries the central control for oesophageal motility; these excitatory and inhibitory fibres supply the oesophageal muscle via intramural neurons; the synaptic arrangement of the inhibitory pathway is more complex than the excitatory one.     

Variation in EMG activity: a hierarchical approach

Recordings of naturally occurring Electromyographic (EMG) signalsare variable. One of the first formal and successful attemptsto quantify variation in EMG signals was Shaffer and Lauder's(1985) study examining several levels of variation but not withinmuscle. The goal of the current study was to quantify the variationthat exists at different levels, using more detailed measuresof EMG activity than did Shaffer and Lauder (1985). The importanceof accounting for different levels of variation in an EMG studyis both biological and statistical. Signal variation withinthe same muscle for a stereotyped action suggests that eachrecording represents a sample drawn from a pool of a large numberof motor units that, while biologically functioning in an integratedfashion, showed statistical variation. Different levels of variationfor different muscles could be related to different functionsor different tasks of those muscles. The statistical impactof unaccounted or inappropriately analyzed variation can leadto false rejection (type I error) or false acceptance (typeII error) of the null hypothesis. Type II errors occur becausesuch variation will accrue to the error, reducing power, andproducing an artificially low F-value. Type I errors are associatedwith pseudoreplication, in which the replicated units are nottruly independent, thereby leading to inflated degrees of freedom,and an underestimate of the error mean square. To address theseproblems, we used a repeated measures, nested multifactor modelto measure the relative contribution of different hierarchicallevels of variation to the total variation in EMG signals duringswallowing. We found that variation at all levels, among electrodesin the same muscle, in sequences of the same animal, and amongindividuals and between differently named muscles, was significant.These findings suggest that a single intramuscular electrode,recording from a limited sample of the motor units, cannot berelied upon to characterize the activity of an entire muscle.Furthermore, the use of both a repeated-measures model, to avoidpseudoreplication, and a nested model, to account for variation,is critical for a correct testing of biological hypotheses aboutdifferences in EMG signals.     

Dynamic muscle force predictions from EMG: an artificial neural network approach

EMG signals of dynamically contracting muscle have never been used to predict experimentally known muscle forces across subjects. Here, we use an artificial neural network (ANN) approach to first derive an EMG–force relationship from a subset of experimentally determined EMGs and muscle forces; second, we use this relationship to predict individual muscle forces for different contractile conditions and in subjects whose EMG and force data were not used in the derivation of the EMG–force relationship; and third, we validate the predicted muscle forces against the known forces recorded in vivo. EMG and muscle forces were recorded from the cat soleus for a variety of locomotor conditions giving a data base from three subjects, four locomotor conditions, and 8–16 steps per subject and condition. Considering the conceptual differences in the tasks investigated (e.g. slow walking vs. trotting), the intra-subject results obtained here are superior to those published previously, even though the approach did not require a muscle model or the instantaneous contractile conditions as input for the force predictions. The inter-subject results are the first of this kind to be presented in the literature and they typically gave cross-correlation coefficients between actual and predicted forces of >0.90 and root mean square errors of <15%, thus they were considered excellent.

From the results of this study, it was concluded that ANNs represent a powerful tool to capture the essential features of EMG–force relationships of dynamically contracting muscle, and that ANNs might be used widely to predict muscle forces based on EMG signals.     

EMG activity of pigeon oesophagus in vivo

At rest, the pigeon cervical oesophagus, which is entirely smooth muscle, shows electric activity. This activity consists of bursts of spikes with frequency increasing in the oral-aboral direction. The bursts are un-phase locked, and there are no slow waves (E.C.A.). The surgical transection of the oesophageal muscular wall does not affect the electric activity even in a disconnected segment. After asphyxia electric activity persists, whereas the aboral gradient of frequency disappears. Therefore, the electric activity is thought to be myogenic in origin, and the frequency gradient nervous in origin. Atropine and neostigmine administration suggests that the cholinergic system modulates the electric activity, but it is not involved in the control of the frequency gradient. On the contrary, hexamethonium administration, by abolishing this gradient, lends support to the idea of a postganglionic atropine-resistant neuronal system responsible for the gradient.     

Patterns of muscle activity during different behaviors in chicks: implications for neural control

The large behavioral repertoire that spans the embryonic and postembryonic stages of development make chicks an ideal system for identifying patterns of muscle activity that are common to different behaviors and those that are behavior-specific. The main goal of this work was to identify the similar and dissimilar aspects of the recruitment patterns and the regulation of muscle activity during three distinct postembryonic behaviors: walking, swimming and airstepping. We identified two synergies that were common to each of these behaviors. The synergies were not disrupted by the absence of FT1 activity in airstepping. Within each synergy the recruitment time, recruitment order and duration of activity were not rigid, but varied according to the context-specific resistance that the leg encountered. Unlike the other muscles, FT2 activity was not recruited as part of the same synergy in each behavior. When weight-bearing contact with the substrate did not occur, as in swimming and airstepping, as well as in walking in chicks with deafferented legs, FT2 activity was not recruited as part of either synergy, but was recruited during the time between them. Although not identical, embryonic motility and hatching motor pattern both show the two synergies described for the postembryonic behaviors. Like the latter behaviors, the synergies tolerated the absence of activity from specific muscles. Thus, we suggest that the CNS produces different behaviors using many of the same muscles by organizing the patterned activity around two common synergies while permitting the different muscles that participate in a synergy to be modified in tandem or on an individual basis. Furthermore, the common synergies are established early during prenatal development in chicks.Abbreviations aIF anterior iliofibularius - CF caudilioflexorius - CNS central nervous system - EMG electromyogram - FT femorotibialis - GL gastrocnemius lateralis - P1 protraction 1 - P2 protraction 2 - pIF posterior iliofibularis - R retraction - SA sartorius - TA tibialis anterior - pIF posterior iliofibularis - ms millisecond     

Influence of foam thickness on the control of EMG activity during a step-down task in females

Compliant foams can be used to mitigate ground reaction forces. However, it is unknown how foam surfaces influence the modulation of leg muscle activity. Thus, the current study aimed to investigate how the neuromuscular system managed changes in expected loading due to various thickness of foam placed on the landing surface during a step down task. The surface electromyographic signal (sEMG) pre-activation duration and the root mean square (RMS) amplitude of tibialis anterior (TA), lateral gastrocnemius (LG), and vastus medialis (VM) of 10 active females were measured as they stepped-down with a single leg onto polyurethane foam slabs of varying thickness (0–50 mm). Pre-activation duration was not affected by the thickness of the foam padding. LG RMS amplitude was less in the foam conditions than the control (no– foam) condition, with the greatest reduction observed for the 50 mm foam condition. In some trials, the muscles remained active throughout the step-down task. In such instances, a sEMG onset time and thus a pre-activation duration could not be determined. All foam conditions significantly increased the odds of continuous muscle activity above that of the no-foam condition. The results indicate that foam surfaces may alter the modulation of muscle activity during step-down tasks.     

The extraction of neural strategies from the surface EMG.

This brief review examines some of the methods used to infer central control strategies from surface electromyogram (EMG) recordings. Among the many uses of the surface EMG in studying the neural control of movement, the review critically evaluates only some of the applications. The focus is on the relations between global features of the surface EMG and the underlying physiological processes. Because direct measurements of motor unit activation are not available and many factors can influence the signal, these relations are frequently misinterpreted. These errors are compounded by the counterintuitive effects that some system parameters can have on the EMG signal. The phenomenon of crosstalk is used as an example of these problems. The review describes the limitations of techniques used to infer the level of muscle activation, the type of motor unit recruited, the upper limit of motor unit recruitment, the average discharge rate, and the degree of synchronization between motor units. Although the global surface EMG is a useful measure of muscle activation and assessment, there are limits to the information that can be extracted from this signal.     

Quantitative analysis of four EMG amplifiers

Four typical EMG amplifiers were tested quantitatively to observe the diversity and specificity of available equipment. Gain, phase, common mode rejection ratio (CMRR) and noise characteristics were measured for each device. Various gain and phase responses were observed, each best suited to specific application areas. For all amplifiers, the CMRR was shown to decrease dramatically in the presence of input impedance mismatches of more than 10 kΩ between the two electrodes. Because such impedance mismatches are common on the skin surface, these results indicate that proper skin preparation is required to maximize the noise rejection capabilities of the tested amplifiers.     

Methodological survey of automatic EMG analysis

This paper describes a methodological survey of different methods, manual and computer-aided for quantitative MUP analysis up to the present. Due to different recording techniques and facilities for signal analysis individual laboratories have developed their own methods. Although most of the methods are still in the research phase, they provide a valuable contribution to clinical possibilities. The most important effect of the computer in electromyography is the fact that it emphasizes a new trend in quantitative EMG analysis also in routine clinical assessment.     

The methods of surface EMG analysis

The use of surface emg as a tool for quantification is described. First, the specific advantages of the surface emg are discussed. Techniques for analysis of the emg signal which estimate and detect the action potentials of the individual motor units and estimate some global properties of muscle activity are reviewed. A survey of data on relations between the properties of motor unit action potential, the properties of motor unit activity and the results of signal processing are given.     

Evidence for extrinsic control of oesophageal primary peristalsis

The r?le of both peripheral and central mechanism in the control of primary peristalsis was studied in pigeon cervical oesophagus. The results from the transection of oesophageal muscular wall and of extrinsic nerves suggest that: primary peristalsis is programmed centrally. extrinsic motor input is carried in glossopharyngeal nerves and distributed separately at each oesophageal level through intramural neurons. intramural neurons do not seem capable of propagating the peristaltic sequence irrespective of the central control.