Four quantitative EMG methods and theirs individual parameter diagnostic value

Quantitative electromyography (EMG) usage in daily clinical medicine can exclude the investigation results influencing by the electromyographer's subjective factor in needle EMG. The aim of our study was to compare the diagnostic efficiency of these quantitative EMG methods which have found some more consistent application in routine neurologic practice. We have investigated 35 healthy subjects and 59 patients with two basic types of neuromuscular disorders (neuropathies and myopathies) by means of four quantitative EMG methods: 1--modified Buchthal's low threshold MUAPs (motor unit action potentials) analysis; 2--interference EMG pattern Dorfman's and McGill's limited decomposition; 3--interference EMG pattern spectral analysis; 4--interference EMG pattern turns-amplitude analysis. In results analysis parameter's 95% confidence intervals were calculated by Campbell and Gardner and the difference between three subject groups (controls, neuropathies, myopathies) was evaluated by special multidimensional statistics (Hotelling T2 test) using simultaneously all tested parameters of four quantitative EMG methods. The modified Buchthal's low threshold MUAPs analysis was the most effective method in discovering neuropathy and myopathy with area as the best discriminating parameter. The diagnostic power in neuropathies may be increased using selected quantitative EMG methods or theirs individual parameters combinations. Several aspects of applyied quantitative EMG methods and aquired data statistical analysis are discussed.     

Evaluation of motor unit firing rates by standard concentric needle electromyography.

Motor unit firing rates at slight voluntary contraction were studied by standard concentric needle electromyography. Employing digital signal analysis techniques firing rates of motor units (MU) could be evaluated as long as four or less different MUs were activated in the vicinity of the concentric needle electrode. The extension of the recording area is defined by the recording properties of the electrode and the upper limit of rise-time for all MUPs being evaluated. Distant MUs, generating volume conducted potentials with rise-times greater than 0.8 ms, were excluded. In biceps muscles of 15 healthy controls the firing rate of the MU activated first was evaluated at that moment, when a second MU was recruited and was found to be 12.1 +/- 2.1 Hz (mean +/- S.D., n = 40). The firing rate of the fastest MU out of 2, 3, or 4 simultaneously active MUs was 10.7 +/- 2.5 Hz, 10.9 +/- 2.5 Hz and 10.6 +/- 2.4 Hz respectively. Hence at low innervation level there is no increase of firing rate with rising number of activated MUs. The upper normal limit of MU firing rate (3 sigma interval) is calculated as 17 Hz, irrespective whether 1, 2, 3 or 4 MUs are active within the recording area. Fifteen patients with partially denervated biceps muscles were investigated. Maximal firing rates were increased in 10 patients, all showing moderate or severe paresis (grade 1-3). In 10 patients suffering from myopathies firing rates always were normal. The presented data may serve as an additional criterion in evaluating MU firing rates during standard clinical EMG.     

Disintegration of the motor unit in post-polio syndrome. Part II. Electrophysiological findings in patients with post-polio syndrome

The aim of the study is to investigate the motor unit abnormalities in late postpolio muscular atrophy (PPMA) as compared to those found in patients who had polio 20-30 years prior to examination without any new clinical signs. The quantitative concentric needle EMG and a single fiber EMG techniques were employed. Spontaneous activity, the parameters of individual motor units potentials (MUP), number of complex potentials and their stability, jitter and blocking as well as fiber density (FD) have been evaluated. In PPMA patients (5 subjects) we found in newly weakened muscles: spontaneous activity, high percentage of complex potentials, increased jitter, increased FD. The EMG findings in muscles previously affected but without any signs of progression have been similar. In the patients with stable nonprogressing postpolio muscle atrophy (12) all MUP-s parameters indicated changes similar to PPMA but less marked in initially affected muscle with complete or incomplete recovery as well as sometimes in initially clinically unaffected muscles. These findings suggest that the signs of ongoing reinnervation processes persist many years after polio and that PPMA occurring later in life represents disintegration of the previously reinnervated motor units. It is still unclear whether this disintegration depends on decompensation by different factors of fully reinnervated motor units or whether most of the motor units after polio never regained a stable reinnervation.     

Depth and intensity of equivalent current dipoles estimated through an inverse analysis of surface electromyograms using the image method

The depth and intensity of equivalent current dipoles that can create the surface potentials of active motor units in human skeletal muscles are estimated through an inverse analysis of surface electromyographic (EMG) potentials in an attempt to measure detailed muscular activity non-invasively. The inverse analysis is conducted by repetition of forward analyses. In the study, the image method is used for forward analysis, because it is the simplest potential calculation method for electric currents in a semi-infinite volume conductor. Using this method, surface EMG potentials are calculated for current sources assumed to be located in a muscle. An inverse analysis is then carried out by searching for the depth and intensity of such current sources that would minimise the sum of squares difference between measured and calculated surface EMG potentials. The inverse analysis is applied to surface EMG potentials measured from the biceps brachii of three healthy subjects. As a result, the individual current sources are estimated to be 2.7 +/- 1.6 mm deep and 0.5 +/- 0.9 nAm in intensity, whereas the total current intensity for individual motor units is 2.4 +/- 2.9 nAm.     

Depth and intensity of equivalent current dipoles estimated through an inverse analysis of surface electromyograms using the image method

The depth and intensity of equivalent current dipoles that can create the surface potentials of active motor units in human skeletal muscles are estimated through an inverse analysis of surface electromyographic (EMG) potentials in an attempt to measure detailed muscular activity non-invasively. The inverse analysis is conducted by repetition of forward analyses. In the study, the image method is used for forward analysis, because it is the simplest potential calculation method for electric currents in a semi-infinite volume conductor. Using this method, surface EMG potentials are calculated for current sources assumed to be located in a muscle. An inverse analysis is then carried out by searching for the depth and intensity of such current sources that would minimise the sum of squares difference between measured and calculated surface EMG potentials. The inverse analysis is applied to surface EMG potentials measured from the biceps brachii of three healthy subjects. As a result, the individual current sources are estimated to be 2.7±1.6 mm deep and 0.5±0.9 nAm in intensity, whereas the total current intensity for individual motor units is 2.4±2.9 nAm.     

Metabolic myopathies

The most frequent metabolic myopathies of children and adults (glycogenoses; neutral fat myopathies; "mitochondrial" myopathies) are reviewed. In glycogenoses and neutral fat myopathies the most prominent histological feature is represented by a vacuolation of muscle fibres, vacuoles being filled with glycogen or neutral fat. Enzyme defects of glycogenoses are known. In some neutral fat myopathies, an involvement of carnitine metabolism can be found; in many other cases, biochemical investigations have failed to identify the enzyme defect(s), or have demonstrated the contemporaneous involvement of mitochondria ("mitochondrial" myopathy). The large group of "mitochondrial" myopathies is built up of many heterogeneous polygenetic syndromes, the appearance of which signalises only an impaired mitochondrial function due to underlying biochemical defect(s). In these cases, accumulations of mitochondria in muscle fibres, easily recognisable with trichrome stain ("ragged-red fibres") may be found. These mitochondria usually present very peculiar ultrastructural changes ("paracrystalline inclusions"). One of the leading clinical symptoms of metabolic myopathies is represented by myoglobinuria. In every case of "idiopathic" rhabdomyolysis, a metabolic myopathy should hence be suspected. The negative result of histological and enzymehistochemical investigations, does not exclude the presence of a metabolic disorder, however. Research in this field requires a very strong cooperation between morphologists and biochemists. Future therapeutical approaches can in fact only come from and through biochemistry.     

Characteristics of motor unit potentials in human skeletal muscle during the denervation-reinnervation process

Traditionally measured parameters of motor unit potentials and parameters of the fast (spike) component of motor units were compared in the common extensor of fingers of 24 patients with chronic progressive diseases of motoneurons or their axons and 12 healthy subjects. The earliest signs of motor unit disorders are shown to be increased in the amplitude, duration, and number of turns in the spike (main) component of potentials. A corrrelation was found to exist between increases in muscle fiber density and in the number of turns. Analysis of the main component parameters indicates that both concentration of muscle fibers in the central zone of motor units and desynchronization of their activity occur in initial phases of the denervation-reinnervation process. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 122, No. 8, pp. 131–134, August, 1996     

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.     

The innervation of skeletal muscles in chickens curarized during early development

Chicken embryos were treated with partially paralysing doses of d-tubocurarine (dtc) from embryonic (E) days 6 to 10. The pattern of innervation of the lateral gastrocnemius (GL) muscle was examined both morphologically and physiologically just before hatching on day E20 or E21. There was a 70% increase in number of surviving motor neurons in the lateral motor column and a 50% increase in the number of myelinated axons in the nerve to GL. The GL muscle was significantly atrophic, with an average weight of 40% of normal. The atrophy was largely due to the reduced size of the muscle fibres. The mean size of the motor units was essentially unchanged or perhaps slightly increased. There was a striking increase in the level of polyneuronal innervation of the muscle fibres, both in terms of number of synaptic sites per fibre and number of axons innervating each site. Spontaneous miniature endplate potentials (mepps) indicated focal innervation of the fibres in the normal muscle. Most fibres in the dtc-treated muscles had mepps of widely varying time courses, and there was no simple relation between amplitude and rise time. Many of the slow mepps were not represented in the endplate potentials evoked by nerve stimulation. The quantal content of the endplate potential (epp) was generally increased in the dtc-treated muscles. The findings are discussed in terms of a retrograde signal from muscle to nerve and its dependence on muscle activity.     

Personality and Individual Differences in Spinal Motoneuronal Excitability

Although individual differences in sensation-seeking are characterized by a wide range of differences in the expression of motor behavior, the psychophysiological correlates of these characteristics have not been extensively explored. In the present investigation the response characteristics of compound muscle action potentials, the H-reflex and associated motor responses, were examined in young adult subjects who were administered the Sensation Seeking Scale (Zuckerman, 1979) and the Eysenck Personality Questionnaire (Eysenck & Eysenck, 1975). Variations in reflex responses were observed using two independent procedures. A paired stimulus method assessed the extent of reflex amplitude recovery at varying pulse intervals. A second method, termed homosynaptic depression, examined motoneuronal excitability in response to trains of pulses delivered at varying rates. The personality groups did not differ with respect to the intensity of stimulation required to elicit muscle action potentials or the nerve conduction velocities of those potentials. High disinhibition and high extraversion groups displayed reduced motoneuronal excitability as assessed by analysis of reflex recovery functions. For extraversion, similar effects were observed with the homosynaptic depression measure. These results demonstrate that individual differences in disinhibition and extraversion can be referred to discrete levels of CNS motor system activity. In this context, stimulus seeking behavior is not distinguished by a need for stimulation (initial hypoexcitability) but reflects instead reduced motor excitability which becomes evident once motoneuronal activity is initiated.     

Kongenitale und andere Myopathien

The myopathies presented here fall into two groups: Congenital myopathies and protein aggregate myopathies. These genetic conditions often require all modern diagnostic investigations, including histology, enzyme histochemistry, immunohistochemistry and electron microscopy to pave the way to an adequate individual molecular analysis and diagnosis. This is necessary to provide the patient and his or her family information about disease-characteristics or even disease-specific features. Distal myopathies, although caused by mutations in different genes, and toxic myopathies as acquired neuromuscular conditions largely provide non-specific morphological features a correct nosological interpretation of which only succeeds with additional non-morphological data.     

Motor evoked potentials in patients with spinal disorders: upper and lower motor neurone affection.

Motor evoked potentials (MEP) following magnetoelectric stimulation allow for detection and quantification of a lesion of the central and peripheral motor pathways. MEP latency is a very sensitive parameter, irrespective whether the lesion affects the upper motor neurone, e.g. in cervical myelopathy, or the lower motor neurone e.g. in cervical or lumbar radiculopathy. However, an increase of MEP latency alone does not allow for a distinction of either upper motor neurone or lower motor neurone affection. We have therefore scrutinized MEP latency and MEP waveform (amplitude, duration, and number of phases) in normal subjects, as well as in patients with cervical myelopathy (upper motor neurone affection: UMNA) and in patients with radiculopathies (lower motor neurone affection, LMNA). The increase of central motor latency compared to normal values was significantly higher in UMNA than in LMNA. MEP following transcranial magnetoelectric stimulation were split up and their duration in relation to M-wave duration was significantly increased in patients with UMNA, yet normal in patients with LMNA. MEP amplitude in relation to M-wave amplitude was significantly decreased in patients with UMNA, yet normal in patients with LMNA. We conclude that cervical myelopathy and cervical or lumbar radiculopathies lead to changes of MEP waveform, which are specific for either upper or LMNA. The analysis of amplitude, duration, and number of phases of MEP following transcranial stimulation increases the diagnostic value of MEP in disorders of the spine affecting the central or proximal peripheral motor pathways.     

Model for decomposition of the motor unit action potential 1 The algorithm

A model for decomposition of the motor unit action potential (MUAP) into its constituent single-fibre action potentials is presented. It finds an optimal fit of a set of simulated single-fibre action potentials (SSFAPs) to the MUAP. The SSFAPs are assumed to originate from muscle fibres at different distances from the electrode, having various delays in time. Two methods for decomposition of the MUAP are derived from this model: first, that the MUAP is decomposed into a fixed set of SSFAPs; and secondly that the MUAP is decomposed into an adaptive, expanding set of SSFAPs. In the second method three steps are used repeatedly. First, the MUAP is cross-correlated with a collection of four SSFAPs. Then the most similar SSFAPs are used to reconstruct the original MUAP. The reconstruction thus obtained is subtracted from the original MUAP to detect activity not yet imitated. This difference (‘residual’) is again used for cross-correlation, restarting in step 1. After a suitable number of iterations, the MUAP is optimally imitated by a set of SSFAPs. The set of SSFAPs, obtained as described, is assumed to give information about underlying anatomical and physiological data (such as fibre number, fibre density, impulse dispersion) of the motor unit under study.     

Detection of movement-related potentials from the electro-encephalogram for possible use in a brain-computer interface

Brain-computer interfaces are devices for enabling patients with severe motor disorders to communicate with the world. One method for operating such devices is to use movement-related potentials that are generated in the brain when the patient moves, or imagines a movement of, one of his limbs. An algorithm for detecting movement-related potentials using a small number of EEG channels was developed. This algorithm is a combination of the matched filter, a non-linear transformation previously developed as part of a similar detector, and a classifier. The algorithm was compared with previous designs of similar detectors by both theoretic analysis and off-line evaluation of performance on data recorded from five subjects. It is shown that the performance of the algorithm was superior to that of previous methods, improving the area under the receiver operating characteristic curve to 87.8%, an improvement of 25% compared with the best previously suggested detection method. Finally, the probable sources for false detections were identified, and possible ways to minimise them are proposed.     

General-purpose filter design for neural prosthetic devices

Brain-driven interfaces depend on estimation procedures to convert neural signals to inputs for prosthetic devices that can assist individuals with severe motor deficits. Previous estimation procedures were developed on an application-specific basis. Here we report a coherent estimation framework that unifies these procedures and motivates new applications of prosthetic devices driven by action potentials, local field potentials (LFPs), electrocorticography (ECoG), electroencephalography (EEG), electromyography (EMG), or optical methods. The brain-driven interface is described as a probabilistic relationship between neural activity and components of a prosthetic device that may take on discrete or continuous values. A new estimation procedure is developed for action potentials, and a corresponding procedure is described for field potentials and optical measurements. We test our framework against dominant approaches in an arm reaching task using simulated traces of ensemble spiking activity from primary motor cortex (MI) and a wheelchair navigation task using simulated traces of EEG-band power. Adaptive filtering is incorporated to demonstrate performance under neuron death and discovery. Finally, we characterize performance under model misspecification using physiologically realistic history dependence in MI spiking. These simulated results predict that the unified framework outperforms previous approaches under various conditions, in the control of position and velocity, based on trajectory and endpoint mean squared errors.     

The number of active motor units and their firing rates in voluntary contraction of human brachialis muscle

To make clear the control mechanism of force generation in human muscle, the electrical activity of the brachialis muscle was studied at various levels of contraction force by recording single motor unit discharges as well as mass electromyograms (EMGs). The firing rate of motor units increased with force along an S-shaped curve. At low levels of force, motor units increased their firing rates steeply with force. At intermediate levels of force, each motor unit increased its firing rate linearly with force at lower rates. As the maximum of force was approached, the firing rate increased very steeply, reaching as high as 50 Hz or more. By applying a new method of statistical processing to mass EMGs, the number of active motor units and the size of action potential were estimated at each level of force. The number of active motor units increased monotonously with muscle force. Motor units recruited at high levels of force had larger amplitudes of action potentials than those recruited at lower levels. Calculations were made to determine how the relative contribution to an increase in muscle force is varied between recruitment and the increase in firing rate. The contribution of recruitment gradually decreased with the increase in force. Up to about 70% of the maximum force, recruitment is the major mechanism for increasing the force of contraction.     

shocked Gene is required for the function of a premotor network in the zebrafish CNS

The analysis of behavioral mutations in zebrafish can be a powerful strategy for identifying genes that regulate the function and development of neural circuits in the vertebrate CNS. A neurophysiological analysis of the shocked (sho) mutation that affects the initiation of swimming after mechanosensory stimulation was undertaken to identify the function of the sho gene product in the developing motor circuitry. The cutaneous Rohon-Beard (RB) mechanosensory neurons responded normally to stimulation, and muscle fibers were unaffected in sho embryos, suggesting that the output of the CNS is abnormal. Indeed whole cell patch recordings from mutant muscle cells showed normal spontaneous miniature endplate potentials, but abnormal touch-evoked endplate potentials. Furthermore, motor neuron recordings showed that bursts of rhythmic action potentials from synaptically dependent depolarizations are initiated in wild-type motor neurons after sensory stimulation or bath application of N-methyl-D-aspartate. These bursts presumably correspond to bouts of swimming. In sho motor neurons, the touch-evoked depolarizations were not sustained, resulting in an abbreviated burst of action potentials. The defective responses were not due to any obvious defect in sho motor neurons because their basic properties were normal. These results suggest that in sho embryos, there is aberrant motor processing within the CNS and that normal motor processing requires the sho gene product.     

Changes of cortical activity when executing learned motor sequences

Summary Fifteen right-handed subjects performed a learned sequence of four movements (flex index finger, extend hand, extend index finger, flex hand) either with their left or their right hand. The sequence of movements had to be continuously repeated for 20 s (period of execution). In the beginning of each period of execution large negative DC potentials were recorded in positions located above the mesial fronto-central cortex (Cz) and the sensorimotor hand areas of either hemisphere (C3 and C4). In contrast, DC potentials were absent in Cz at the end of the period of execution. In recordings from a position above the sensorimotor hand area contralateral to the performing side, negative DC potentials declined to some extent during task execution but were still present at the end of the period. Variations of both the amplitude and topography of negative cortical DC potentials during task-execution indicate changes of both the size and pattern of cortical activity. These findings were consistently found at both the beginning and end of the experiment. Motor performance as quantified by movement times and inter-onset latencies of movements showed no change, either during the periods of execution or when comparing the beginning of the experiment with the end. Conclusions are: (1) the execution of a learned motor sequence task cannot be associated with a particular size and pattern of cortical activity. (2) A pronounced decline of neural activity in the mesial, fronto-central area constitutes the predominant feature of the changes of cortical activity during the period of execution. (3) Since motor programs and plans are pre-established, changes of cortical activity reflect changing levels or modes of motor control.     

Actual and mental motor preparation and execution: a spatiotemporal ERP study

Studies evaluating the role of the executive motor system in motor imagery came to a general agreement in favour of the activation of the primary motor area (M1) during imagery, although in reduced proportion as compared to motor execution. It is still unclear whether this difference occurs within the preparation period or the execution period of the movement, or both. In the present study, EEG was used to investigate separately the preparation and the execution periods of overt and covert movements in adults. We designed a paradigm that randomly mixed actual and kinaesthetic imagined trials of an externally paced sequence of finger key presses. Sixty channel event-related potentials were recorded to capture the cerebral activations underlying the preparation for motor execution and motor imagery, as well as cerebral activations implied in motor execution and motor imagery. Classical waveform analysis was combined with data-driven spatiotemporal segmentation analysis. In addition, a LAURA source localization algorithm was applied to functionally define brain related motor areas. Our results showed first that the difference between actual and mental motor acts takes place at the late stage of the preparation period and consists of a quantitative modulation of the activity of common structures in M1. Second, they showed that primary motor structures are involved to the same extent in the actual or imagined execution of a motor act. These findings reinforce and refine the functional equivalence hypothesis between actual and imagined motor acts.This study was supported by a grant (1114–56777.99) from the Swiss National Science Foundation and by the Programme Commun de Recherche en Génie Biomédical 1999–2002     

EMG dynamics in polymyositis and dermatomyositis in adults

In order to analyze the EMG dynamics in acute and chronic polymyositis 44 patients were examined. Thirty-four were seen in the acute stage, 28 in the chronic stage and 18 serially. Investigations included quantitative electromyography using the Polish minicomputer "ANOPS 105" connected to a DISA electromyograph. Additionally fiber density was analyzed by single fiber electromyography in the chronic stage only. The acute stage findings confirmed the observations of earlier authors with the classical expression of excessive spontaneous activity, polyphasic potentials of short duration and low amplitude. In the chronic stage, motor unit potentials with increased duration and amplitude and with late components of the type seen in satellite potentials were noted. This was compared with the increased fiber density found at this stage. Additionally, in some muscles in the chronic stage, motor unit potentials were seen with increased duration, but also a reduction in the mean amplitude of motor unit potentials counted by the automatic analysis method. The decreased amplitude of the motor unit potentials in the chronic polymyositis may be the result of the smaller size of regenerating muscle fibers.