Simulation analysis of interference EMG during fatiguing voluntary contractions. Part II--changes in amplitude and spectral characteristics.

Capabilities of amplitude and spectral methods for information extraction from interference EMG signals were assessed through simulation and preliminary experiment. Muscle was composed of 4 types of motor units (MUs). Different hypotheses on changes in firing frequency of individual MUs, intracellular action potential (IAP) and muscle fibre propagation velocity (MFPV) during fatigue were analyzed. It was found that changes in amplitude characteristics of interference signals (root mean square, RMS, or integrated rectified value, IEMG) detected by intramuscular and surface electrodes differed. RMS and IEMG of surface detected interference signals could increase even under MU firing rate reduction and without MU synchronisation. IAP profile lengthening can affect amplitude characteristics more significantly than MU firing frequency. Thus, an increase of interference EMG amplitude is unreliable to reflect changes in the neural drive. The ratio between EMG amplitude and contraction response can hardly characterise the so-called 'neuromuscular efficiency'. The recently proposed spectral fatigue indices can be used for quantification of interference EMG signals. The indices are practically insensitive to MU firing frequency. IAP profile lengthening and decrease in MFPV enhanced the index value, while recruitment of fast fatigable MUs reduced it. Sensitivity of the indices was higher than that of indices traditionally used.     

Membrane voltage changes in a compartmental chain model of a neurone

A mathematical model of the neurone has been developed using the method of subdivision of the neurone into a number of equivalent circuit compartments. Compartmental characteristics have been investigated by calculating the shape indices of the output produced in response to a given somatic input conductance change. A generalised form of compartmental chain has been chosen to allow calculation of the shape indices produced by a variety of geometrical configurations including the straight and tapering chain forms. Equations have been deduced from the computations made on a CDC 6600 computer relating the peak amplitude of the output response to the compartmental diameter for both the straight and tapering chain forms. The effect of variation in the location of the input conductance injection site has also been related to the peak amplitude of the somatic response. The optimum characteristics of the input conductance pulse shape have been computed initially using a rectangular pulse and later the more physiologically relevant double exponential shape. The effect of alteration in the end compartmental terminal impedances over the range from open to short circuit conditions was also calculated. The establishment of optimum single compartmental chain criteria allows the future investigation of multiple chain and pyramidal cell configurations.     

Action potentials of the heart atria and ventricles of Rana temporaria frogs and Cyprinus carpio carp]

Using microelectrode technique, studies have been made on electrophysiological indices (amplitude of AP, amplitude of the plateau, latent period of AP, duration of maximal depolarization, duration of repolarization at different levels) of cells of isolated atrium and ventricles of the carp during both the spontaneous activity and electrical stimulation. The obtained amplitude-temporal parameters were compared to those of the heart in the frog R. temporaria. It was found that the amplitude of AP, the amplitude of the plateau and the duration of the latent period of AP in both the atrium and ventricles of the carp significantly (p less than 0.01) differ from the corresponding indices of the frog. On the contrary, the duration of maximal depolarization and repolarization in cells from homologous parts of the heart is very close in the species investigated.     

A Time Course Analysis of the Electrophysiological Properties of Neurons Differentiated from Human Induced Pluripotent Stem Cells (iPSCs)

Many protocols have been designed to differentiate human embryonic stem cells (ESCs) and human induced pluripotent stem cells (iPSCs) into neurons. Despite the relevance of electrophysiological properties for proper neuronal function, little is known about the evolution over time of important neuronal electrophysiological parameters in iPSC-derived neurons. Yet, understanding the development of basic electrophysiological characteristics of iPSC-derived neurons is critical for evaluating their usefulness in basic and translational research. Therefore, we analyzed the basic electrophysiological parameters of forebrain neurons differentiated from human iPSCs, from day 31 to day 55 after the initiation of neuronal differentiation. We assayed the developmental progression of various properties, including resting membrane potential, action potential, sodium and potassium channel currents, somatic calcium transients and synaptic activity. During the maturation of iPSC-derived neurons, the resting membrane potential became more negative, the expression of voltage-gated sodium channels increased, the membrane became capable of generating action potentials following adequate depolarization and, at day 48–55, 50% of the cells were capable of firing action potentials in response to a prolonged depolarizing current step, of which 30% produced multiple action potentials. The percentage of cells exhibiting miniature excitatory post-synaptic currents increased over time with a significant increase in their frequency and amplitude. These changes were associated with an increase of Ca²⁺ transient frequency. Co-culturing iPSC-derived neurons with mouse glial cells enhanced the development of electrophysiological parameters as compared to pure iPSC-derived neuronal cultures. This study demonstrates the importance of properly evaluating the electrophysiological status of the newly generated neurons when using stem cell technology, as electrophysiological properties of iPSC-derived neurons mature over time.     

Measuring activity in olfactory receptor neurons in Drosophila: Focus on spike amplitude

Olfactory responses at the receptor level have been thoroughly described in Drosophila melanogaster by electrophysiological methods. Single sensilla recordings (SSRs) measure neuronal activity in intact individuals in response to odors. For sensilla that contain more than one olfactory receptor neuron (ORN), their different spontaneous spike amplitudes can distinguish each signal under resting conditions. However, activity is mainly described by spike frequency.Some reports on ORN response dynamics studied two components in the olfactory responses of ORNs: a fast component that is reflected by the spike frequency and a slow component that is observed in the LFP (local field potential, the single sensillum counterpart of the electroantennogram, EAG). However, no apparent correlation was found between the two elements.In this report, we show that odorant stimulation produces two different effects in the fast component, affecting spike frequency and spike amplitude. Spike amplitude clearly diminishes at the beginning of a response, but it recovers more slowly than spike frequency after stimulus cessation, suggesting that ORNs return to resting conditions long after they recover a normal spontaneous spike frequency. Moreover, spike amplitude recovery follows the same kinetics as the slow voltage component measured by the LFP, suggesting that both measures are connected.These results were obtained in ab2 and ab3 sensilla in response to two odors at different concentrations. Both spike amplitude and LFP kinetics depend on odorant, concentration and neuron, suggesting that like the EAG they may reflect olfactory information.     

The contingency of parameters of human encephalograms and Schumann resonance electromagnetic fields revealed in monitoring studies

The contingency of variations in amplitude—frequency parameters of the main modes of extremely-low-frequency resonances of an ionospheric waveguide (Schumann resonances) and changes in human encephalograms in the frequency range of 6–16 Hz has been studied. The results obtained with the use of synchronized monitoring suggest that such contingency, expressed as indices of cross-correlation function, is statistically significant, varying from 0.12 to 0.65 at α = 0.95. It has been established that contingency is largely determined by the current level of solar and geomagnetic activity.     

The relationship between flash evoked potentials and evoked amplitude modulation patterns of an applied UHF electromagnetic field in the rat

Pilot studies demonstrate evidence that the electrophysiological processes associated with flash stimulation of the central nervous system (CNS) of rats, as seen in the recordings of visual-evoked potentials, may also be detectable using an ultrahigh frequency electromagnetic field (UHFEMF). Patterns of amplitude modulation of an applied UHFEMF, when recorded and averaged, show strong correlations with simultaneously recorded evoked potentials. The data support the hypothesis that the UHFEMF amplitude is altered in a dynamic fashion by the tissue's electrophysiological processes that are involved with the generation of CNS electric fields.     

Effect of the cerebellum on the motor activity of the stomach in the scorpion fish, Scorpaena porcus

It has been shown that after cerebellectomy or electrical stimulation of the cerebellum in the fish the motor activity of its stomach undergoes significant changes. From the 1st to the 5th day after cerebellectomy, the frequency and amplitude of the stomach contractions decrease. These indices return to the initial level only to the 7th day after the operation. Electrical stimulation of the cerebellum decreases the frequency, but not the amplitude of the stomach contractions. These changes take place within the 1st hour after stimulation. Electrical stimulation of the skin of the head of the fish does not affect motor activity of the stomach.     

Mathematical Modeling of Heterogeneous Electrophysiological Responses in Human β-Cells

Electrical activity plays a pivotal role in glucose-stimulated insulin secretion from pancreatic -cells. Recent findings have shown that the electrophysiological characteristics of human -cells differ from their rodent counterparts. We show that the electrophysiological responses in human -cells to a range of ion channels antagonists are heterogeneous. In some cells, inhibition of small-conductance potassium currents has no effect on action potential firing, while it increases the firing frequency dramatically in other cells. Sodium channel block can sometimes reduce action potential amplitude, sometimes abolish electrical activity, and in some cells even change spiking electrical activity to rapid bursting. We show that, in contrast to L-type -channels, P/Q-type -currents are not necessary for action potential generation, and, surprisingly, a P/Q-type -channel antagonist even accelerates action potential firing. By including SK-channels and dynamics in a previous mathematical model of electrical activity in human -cells, we investigate the heterogeneous and nonintuitive electrophysiological responses to ion channel antagonists, and use our findings to obtain insight in previously published insulin secretion measurements. Using our model we also study paracrine signals, and simulate slow oscillations by adding a glycolytic oscillatory component to the electrophysiological model. The heterogenous electrophysiological responses in human -cells must be taken into account for a deeper understanding of the mechanisms underlying insulin secretion in health and disease, and as shown here, the interdisciplinary combination of experiments and modeling increases our understanding of human -cell physiology.     

Individual alpha activity of electroencephalogram and nonverbal creativity

The main objective of present correlational investigation was to clarify relationships between nonverbal creativity indices and individual electroencephalogram alpha activity indices: individual alpha peak frequency, alpha band width, magnitude of alpha desynchronization and alpha spindle indices such as duration, amplitude, variability and skewness. The EEG was recorded in 98 healthy male right-handed subjects. Scores of nonverbal creativity (i. e., fluency, originality, and flexibility) were assessed using the Torrance test of nonverbal performance. The study showed that fluency in creative performance was associated with individual alpha peak frequency and alpha spindles duration, whereas originality and plasticity--with individual alpha band width and spindle amplitude variability. The findings also show that both highest and lowest individual alpha peak frequency indices are associated with enhanced scores of originality. It is suggested that individual alpha activity indices could be presented as individual predictors of fluency, plasticity and originality of nonverbal creativity.     

Assessment of influence of breath holding and hyperventilation on human postural stability with spectral analysis of stabilographic signal

The influence of breath holding and voluntary hyperventilation on the traditional stabilometric parameters and the frequency characteristics of stabilographic signal was studied. We measured the stabilometric parameters on a force platform (“Ritm”, Russia) in the 107 healthy volunteers during quiet breath, voluntary hyperventilation (20 seconds) and maximal inspiratory breath holding (20 seconds). Respiratory frequency, respiratory amplitude and ventilation were estimated with the strain gauge. We found that antero-posterior and medio-lateral sway amplitude and velocity as well as sway surface during breath holding and during quiet breathing were the same, so breath holding didn’t influence the postural stability. However, the spectral parameters in the antero-posterior direction shifted to the high frequency range due to an alteration of the respiratory muscles’ contractions during breath holding versus quiet breath. Voluntary hyperventilation caused a significant increase of all stabilographic indices that implied an impairment of the postural stability. We also found that the spectral indices shifted toward the high-frequency range, and this shift was much greater compared to that during breath holding. Besides, amplitudes of the spectral peaks also increased. Perhaps, such change of the spectral indices was due to distortion of the proprioceptive information because of increased excitability of the nerve fibers during hyperventilation. Maximal inspiratory breath holding caused an activation of the postural control mechanisms. It was manifested as an elevation of the sway oscillations’ frequency with no postural stability changes. Hyperventilation led to the greatest strain of the postural control and to a decrease of the postural stability, which was manifested as an increase of center of pressure oscillations’ amplitude and frequency.     

Staircase potentiation in isolated frog skeletal muscle: power spectral analysis of the evoked compound muscle action potential

1. The mechanical and electrophysiological effects of repetitive, low-frequency electrical stimulation on paired sartorii muscles from small male frogs have been investigated, in vitro. 2. Stimulation for 90 sec at 5 Hz resulted in a progressive rise (staircase) than fall (fatigue) in peak twitch tension. 3. The root mean square amplitude, peak-to-peak amplitude, conduction velocity and mean power frequency of evoked compound muscle action potentials (CMAPs) decreased over the stimulation period. 4. Results suggest that alterations in the shape of the CMAP during repetitive stimulation may contribute to the staircase phenomenon.     

ELECTRICAL POLYSPERMY BLOCK IN SEA URCHINS: NICOTINE AND LOW SODIUM EXPERIMENTS1

Nicotine reduces the amplitude of the fertilization potential in sea urchin eggs, at least in part because it decreases the slope of the current voltage relation of the unfertilized egg membrane. The reduced fertilization potential amplitude provides an electrophysiological explanation for previous observations that nicotine impairs the fast block to polyspermy. The block to polyspermy is also impaired by fertilization in low sodium sea water, a medium which has been reported to reduce fertilization potential amplitude.     

F responses and central motor conduction in multiple sclerosis

Two electrophysiological investigations were used to study 18 patients with multiple sclerosis — F wave characteristics including amplitude, persistence and frequency, which can provide a measure of motoneurone excitability, and magnetic stimulation of the cortex, which enables measurement of conduction along central motor pathways. There was an increase in the mean amplitude and persistence of the F response in patients with abnormal central motor conduction (CMC), although no correlation between the degree of abnormality of CMC and increase in F response amplitude was found. Increase in mean amplitude and persistence of the F response were also found in patients with normal CMC but clinical evidence of a UMN disorder (spasticity and/or weakness); there was no correlation, however, between any single F response characteristic and any particular clinical sign. CMC appears to be the preferred test for detecting subclinical motor lesions in MS: of the patient sides with normal clinical examination, 36% showed abnormal CMC, whereas 23% showed abnormal F responses.     

突触功能障碍大鼠模型EE G 频域特征

本文旨在探讨突触功能障碍大鼠模型在额叶、颞叶和海马这些与认知功能有关的脑区EEG频域特征。先用海马CA1区Aβ1-40加微量注射法制备突触功能障碍模型,用Morris水迷宫行为学测试系统检测其学习记忆能力;然后记录上述脑区的EEG并做频谱分析。结果显示：（1）模型组在第3,4、5、6训练时间段的平均逃避潜伏期较正常组明显延长,和第2训练时间段的相比较,正常组第5训练时间段平均逃避潜伏期明显缩短,模型组到第7训练时间段平均逃避潜伏期开始明显缩短（P〈0．05）;撤去平台后,模型组在原平台所在象限的时间百分比明显降低（P〈0．05）。（2）模型组的EEG表现为α节律慢化,功率下降,其主峰频率左移2Hz,并且额叶、颞叶和海马的δ波和θ波功率不同程度地增高。由此Aβ1-40微量注射法成功制备了突触功能障碍大鼠模型。该模型大鼠的学习记忆能力降低,其频谱特征表现为α节律慢化,功率下降或消失,慢波（δ波和θ波）活动增多,功率不同程度地增高。这些与阿尔茨海默病（Alzheimer’s disease,AD）的EEG一致,可为以后对突触功能障碍时受累皮层进行深入的可塑性和神经再生的研究提供电生理基础。     

Effects and high and low doses of vitamin A on the excitability of frog cardiomyocytes

The effects of the vitamin A lysosomal membrane labilizator on electrophysiological characteristics was investigated on frog cardiomyocytes. Large and small doses of vitamin A produced qualitatively identical effects: decrease of the steepness of action potential (AP) front, decrease of the spike amplitude, shortening of the plateau, decrease of the steepness in the last phase of AP-repolarization. The AP-duration decreased considerably. Large doses of the vitamin also reduced the rest potential level and insignificantly increased the heart contractions frequency. We assume that vitamin A can affect the cardiomyocyte surface membrane permeability, thereby decreasing its excitability due to suppression of the sodium and potassium.     

Frequency characteristics of the saccadic eye movement

Using a piecewise linear approach, individual saccadic eye movements have been Fourier decomposed in an attempt to determine the effect of saccadic amplitude on frequency characteristics. These characteristics were plotted in the traditional Bode plot form, showing gain and phase as a function of frequency for various eye movement amplitudes. Up to about one octave beyond the -3 db gain frequency, the limiting system dynamics represented by the saccadic trajectory of a given amplitude may be considered linear and second order. The -3 db gain frequency was used as a measure of bandwidth, and the -90 degrees phase crossover frequency was used as a measure of undamped natural frequency. These two quantities were used to calculate the damping factor. Both bandwidth and undamped natural frequency decrease with increasing saccadic eye movement amplitude. The damping factor shows no trend with amplitude and indicates approximate critical damping. When compared with the normal variation of characteristics for a given movement, the frequency characteristics of fixed-amplitude saccades showed no generalized trends with changes in direction or DC operating level of movement.     

Effects of beta-catenin on dendritic morphology and simulated firing patterns in cultured hippocampal neurons

Beta-catenin is an intracellular signaling molecule that has been shown to be important in activity-dependent dendritic morphogenesis. Here, we investigate the detailed morphological changes elicited in dendritic arbors of cultured hippocampal neurons by overexpression of beta-catenin, and we simulate the electrophysiological consequences of these changes. Compared to control neurons, cells overexpressing beta-catenin have dendritic arbors with significantly greater surface area and more branches, as well as different topological characteristics. To investigate possible effects of beta-catenin expression on the electrophysiological properties of neurons, we converted confocal images of neurons expressing beta-catenin into computational simulator formats using parameters that evenly distributed voltage-dependent channels across the cells' membranes. In simulated current clamp experiments, somata were injected with a normalized current such that the observed electrophysiological differences in the neurons would be due only to morphological differences. We found that the morphology of beta-catenin-expressing neurons contributes to significantly smaller action potential amplitude and greater sensitivity than seen in control neurons. As a consequence, beta-catenin-expressing neurons tended to exhibit higher spike rates and needed less excitation to induce firing. These findings show that beta-catenin, by modifying dendritic arborization, could have profound influences on the electrophysiological behavior of neurons.     

Improved frequency response of pneumotachometers by digital compensation

To measure impedance one measures or estimates flow, which is commonly done by measuring the pressure drop across a pneumotachometer. The frequency response characteristics of standard pneumotachometer/pressure transducers (PPT) limit their use to relatively low frequencies. Also, the frequency response of PPTs has been reported to be "load" dependent. Thus, the frequency response characteristics measured under "no-load" conditions, which theoretically could be used to compensate subsequent measurements, may not be appropriate for measurements made under loaded conditions. Another method of measuring impedance exists which depends on a reference impedance element other than a pneumotachometer. In this method, an oscillatory flow signal with known amplitude is generated and used to force the system being tested. Unlike PPTs, this oscillatory flow generator (OFG) is a closed system that allows measurements to be made only during breath holding. Our objective was to determine whether the frequency response of a PPT could be compensated using measurements made under no-load conditions, such that it accurately measured an impedance load. The frequency response of the PPT under no-load conditions was measured by the OFG and used to compensate the output of the PPT in subsequent impedance measurements. The compensated PPT was used to measure the impedance of a mechanical structure and the impedances of four human subjects. The impedances of the mechanical structure and the subjects were also measured using the OFG.(ABSTRACT TRUNCATED AT 250 WORDS)     

Modulation analysis of forced non-linear oscillators for biological modelling.

The synchronization of self-sustained oscillations by a forcing oscillation is of interest in a number of biological models. It has been considered for circadian rhythm modelling, heart-rate variability studies and forced breathing experiments. Outside the range of synchronization, conditions of almost-entrainment occur in which changes in amplitude and/or frequency are apparent. It is shown in this paper that such conditions can be analysed as modulation phenomena using the analytical method of harmonic balance. The degree of non-linearity in the self-sustained oscillation affects the nature of modulation, in that increasing distortion gives a trend towards frequency rather than amplitude modulation. The analytical results compare favourably with spectral analysis of simulated oscillators.