Changes In Interspike Intervals Research Articles

Pulse flows of cork neuron populations under microwave irradiation of different intensity

The one-minute effects of the microwave field (wavelength 37.5 cm, power density 0.2-0.3; 0.4; 0.5, and 40 mW/cm2) on the impulse flows of cortical neurons of awake non-immobilized rabbits were investigated. Interpulse intervals were considered within a minute before exposure, during exposure and within one minute after. The changes that occurred on the side of the interspike intervals as a result of these impacts were analyzed. It was found that in the case of irradiation intensities of 0.2-0.3 and 0.4 mW/cm2, the average values of interspike intervals predominantly decreased, and at irradiation intensities of 0.5 and 40 mW/cm2 shifts in the values of interspike intervals of the opposite direction prevailed. The smallest changes in interspike intervals were observed at an intensity of 0.4 mW/cm2. The work shows that microwave irradiation with a one-minute exposure causes rearrangements in the impulse flows of populations of cortical neurons. The rearrangements of neuronal activity that occur under the influence of one-minute microwave irradiation consist of visually predominantly separate shifts during and after exposure with additional fluctuations and indicators within these periods, which is similar to the encephalograms we studied earlier. The studies carried out are necessary for understanding the electromagnetic situation on the Earth and for the analysis of the corresponding space-related problems.

Network-Driven Activity and Neuronal Excitability in Hippocampus of Neonatal Rats with Prenatal Hyperhomocysteinemia

Maternal hyperhomocysteinemia (HHCy) correlated with a number of complications such as abruption placentae, preeclampsia syndrome, in utero fetal death and fetal neural tube defects, cognitive impairment, and neurodegeneration during postnatal development. In the present study, we investigated the effects of prenatal HHCy on electrophysiological features and spontaneous network activity of neurons in hippocampus of rats of the first postnatal week. The analysis of intrinsic electrophysiological properties of pyramidal neurons has shown the decrease of the membrane capacitance and the threshold of generation of action potentials in rats with prenatal HHCy without alteration of the input resistance and resting membrane potential. In trains of action potentials elicited with prolonged current injections, an increase of interspike intervals and a broadening of action potentials during repetitive firing were observed in control neurons. In the neurons of pups with prenatal HHCy, the changes in interspike intervals were not significant and the broadening of action potentials in train was less pronounced. Using extracellular field potential recordings from the hippocampal slices, we found that the network activity in hippocampal slices from rats with prenatal HHCy displayed several abnormalities including the increase in overall neuronal firing and reduction of frequency of giant depolarizing potentials in CA3 regions. We conclude that the increased neuronal excitability and impairment of network activity in hippocampus can underlie neurodevelopmental abnormalities and hyperexcitability in prenatal HHCy.

Effect Of Neuromuscular Electrical Stimulation On Contralateral Motor Unit Activity In Biceps Brachii

Neuromuscular electrical stimulation (NMES) elicits action potentials in intramuscular branches of peripheral nerves. Because the time constant for the strength-duration relation is longer for sensory axons than motor axons, narrow pulse widths (0.2-0.4 ms) preferentially activate motor axons, whereas wider pulse widths (0.5-1 ms) recruit relatively more sensory axons. PURPOSE: The purpose of the study was to determine the influence of NMES pulse width and frequency on the modulation of motor unit (MU) activity in a contralateral limb. The hypothesis was that wide-pulse NMES would cause greater modulation of MU activity due to augmented activation of sensory axons. METHODS: The discharge of action potentials by MUs in the left biceps brachii of young adults (18-35 yrs) was recorded with subcutaneous fine-wire electrodes. The protocol involved subjects performing submaximal isometric contractions to maintain the discharge of an isolated MU. In the middle 5 s of each contraction, NMES was applied to the right biceps brachii with either of two pulse durations (0.2 or 1 ms, each at 40 Hz) and three current intensities (80% motor threshold, 10%, or 20% of maximal voluntary contraction (MVC) force). In an additional group of 7 MUs (recruited between 4-22% MVC force), NMES was applied at both pulse widths and two stimulus frequencies (40 Hz and 100 Hz). The primary outcome was the influence of NMES on the discharge characteristics (mean and coefficient of variation (CV) of interspike interval (ISI)) of the isolated MUs before, during, and after stimulation. RESULTS: Forty-four MUs were discriminated, 16 of which had high recruitment thresholds (≥30% MVC force). Neither narrow- nor wide-pulse NMES elicited a significant change in mean ISI or CV for ISI. For example, mean ISI during an NMES-evoked contraction at 10% MVC force was 11.4 ms, 12.3 ms, and 11.8 ms before, during, and after stimulation (respectively) for narrow pulses and 11.4 ms, 12.3 ms, and 12.0 ms for wide pulses. Similarly, CV for ISI was 20.3%, 20.2%, and 21.2% for narrow pulses and 19.4%, 18.7%, and 19.9% for wide pulses. Moreover, stimulus frequency did not influence the discharge characteristics of the isolated MUs. CONCLUSION: NMES applied to the right biceps brachii did not influence the discharge characteristics of motor units in the left biceps brachii during brief voluntary contractions.

Ouabain modulation of snail Br neuron bursting activity after the exposure to 10 mT static magnetic field revealed by Higuchi fractal dimension.

Aim of this study was to investigate the application of normalized mean of the empirical Higuchi fractal dimension (FD) distributions, as a new approach to analyze the spontaneous bioelectrical activity of garden snail (Helix pomatia) Br neuron. The effect of ouabain on modulation of Br neuron bursting activity before and after the exposure to 10 mT static magnetic field (SMF) was observed by analyzing the following parameters: action potential (AP), interspike interval (ISI) and interbursting interval (IBI) components. Normalized mean of the empirical FD distributions were formed for the following experimental conditions: Control 1, Ouabain 1, Control 2, SMF 2, ASMF 2, Control 3, SMF 3 and Ouabain ASMF 3. Our main results have shown that ouabain without SMF induced increase in participation of AP and a decrease in participation of IBI components compared to the first control condition. However, in the presence of 10 mT SMF, ouabain-induced changes of measured parameters of Br neuron activity were less pronounced compared to the third control condition. We have shown that normalized mean of the empirical FD distributions is a useful method for detecting the changes in AP, ISI, and IBI components of complex bursting activity in altered physiological states.

Effects of Transient Receptor Potential-Like Current on the Firing Pattern of Action Potentials in the Hodgkin-Huxley Neuron during Exposure to Sinusoidal External Voltage

Transient receptor potential vanilloid-1 (TRPV1) channels play a role in several inflammatory and nociceptive processes. Previous work showed that magnetic electrical field-induced antinociceptive [corrected] action is mediated by activation of capsaicin-sensitive sensory afferents. In this study, a modified Hodgkin-Huxley model, in which TRP-like current (ITRP) was incorporated, was implemented to predict the firing behavior of action potentials (APs), as the model neuron was exposed to sinusoidal changes in externally-applied voltage. When model neuron is exposed to low-frequency sinusoidal voltage, increased maximal conductance of ITRP can enhance repetitive bursts of APs accompanied by a shortening of inter-spike interval (ISI) in AP firing. The change in ISIs with number of interval is periodic with the phase-locking. In addition, increased maximal conductance of ITRP can abolish chaotic pattern of AP firing in model neuron during exposure to high-frequency voltage. The ISI pattern is converted from irregular to constant, as maximal conductance of ITRP is increased under such high-frequency voltage. Our simulation results suggest that modulation of TRP-like channels functionally expressed in small-diameter peripheral sensory neurons should be an important mechanism through which it can contribute to the firing pattern of APs.

Firing rate control of a neuron using a linear proportional-integral controller

Some electrophysiology experiments require periodically firing neurons. One example is when measuring a neuron's phase response curve (PRC) where a neuron is stimulated with a synaptic input and the perturbation in the neuron's period is measured as a function of when the stimulus is applied. However, even regular spiking cells have considerable variations in their period. These variations can be categorized into two types: jitter, which characterizes the rapid changes in interspike intervals (ISIs) from spike to spike, and drift, which is a slow change in firing rate over seconds. The jitter is removed by averaging the phase advance of a synaptic input applied at a particular phase several times. The drift over long time scales results in a systematic change in the period over the duration of the experiment which cannot be removed by averaging. To compensate for the drift of the neuron over minutes, we designed a linear proportional-integral (PI) controller to slowly adjust the applied current to a neuron to maintain the average firing rate at a desired ISI. The parameters of the controller were calculated based on a first-order discrete model to describe the relationship between ISI and current. The algorithm is demonstrated on pyramidal cells in the hippocampal formation showing ISIs from the neuron in an open loop (constant applied current) and a closed loop (current adjusted by a spike rate controller). The advantages of using the controller can be summarized as: (1) there is a reduction in the transient time to reach a desired ISI, (2) the drift in the ISI is removed allowing for long experiments at a desired spiking rate and (3) the variance is diminished by removing the slow drift. Furthermore, we implemented an auto-tuning algorithm that estimates in real time the coefficients for each clamped neuron. We also show how the controller can improve the PRC estimation. The program runs on Real-Time eXperiment Interface (RTXI), which is Linux-based software for real-time data acquisition and control applications.

Firing rate control of a neuron using a linear Proportional-Integral (PI) controller

Controlling the firing rate of a neuron is useful for experiments where you would like to see how a small perturbation to the neuron deviates it from its normal period. This is used to characterize phase response curves (PRCs). PRCs can be used to predict how networks of neurons will synchronize, which help in understanding dynamical diseases as epilepsy. In PRC experiments, it is necessary first to apply a constant current in order to make the neuron to fire at a desired constant frequency and then series of short perturbations are applied to find the causal relationship between the timing of the perturbation and the change in the natural period of the neuron. Cells that spike regularly are preferred for this experiment because they tend to keep a constant interspike interval (ISI) at a given constant current. However, even when constant current is applied there are small variations in the ISI that obscure or confound the change of the period caused by the perturbations. These variations can be broken into two types, jitter, which characterizes the rapid changes in interspike intervals from spike to spike, and drift, which characterizes the slow changes in firing rate of the neuron over the time scales in which we measure the phase response curves, on the order of minutes. We designed a linear Proportional-Integral (PI) controller to remove the slow drift and maintain the neuron at a desired firing rate by controlling the current applied to the neuron. We measured the change in ISI in response to steps of constant current. A discrete first order model was fit to the measured response. Then, the proportional and integral coefficients were estimated using a z-domain analysis to obtain critical damping of the neuron’s response. When the controller is on, the histogram of ISI is centered at the set value and also is narrower than using constant current, which implies variance reduction. The PI controller was then tested first on a model neuron and then and then implemented in a dynamic clamp and tested on pyramidal neurons from hippocampal rat slices. Furthermore, we implemented an auto-tuning algorithm that will estimate the coefficients on line. The program runs on Real Time eXperiment Interface (RTXI), which is a real-time Linux based software system for hard real-time data acquisition and control applications. The RTXI PI control module we have made will be available to the community trough the rtxi website.

Activity-Dependent Modulation of Axonal Excitability in Unmyelinated Peripheral Rat Nerve Fibers by the 5-HT(3) Serotonin Receptor

Activity-dependent fluctuations in axonal excitability and changes in interspike intervals modify the conduction of trains of action potentials in unmyelinated peripheral nerve fibers. During inflammation of a nerve trunk, long stretches of axons are exposed to inflammatory mediators such as 5-hydroxytryptamine [5-HT]. In the present study, we have tested the effects of m-chlorophenylbiguanide (mCPBG), an agonist at the 5-HT(3) serotonin receptor, on activity- and potential-dependent variations in membrane threshold and conduction velocity of unmyelinated C-fiber axons of isolated rat sural nerve segments. The increase in axonal excitability during application of mCPBG was much stronger at higher frequencies of action potentials and/or during axonal membrane hyperpolarization. The effects on the postspike recovery cycle also depended on the rate of stimulation. At an action potential frequency of 1 Hz or in hyperpolarized axons, mCPBG produced a loss of superexcitability. In contrast, at 0.33 Hz, a small increase in the postspike subexcitability was observed. Similar effects on excitability changes were found when latency instead of threshold was recorded, but only at higher action potential frequencies: at 1.8 Hz, mCPBG increased conduction velocity and reduced postspike supernormality. The latter effect would increase the interspike interval if pairs of action potentials were conducted along several cm in an inflamed nerve trunk. These data indicate that activation of axonal 5-HT(3) receptors not only enhances membrane excitability but also modulates action potential trains in unmyelinated, including nociceptive, nerve fibers at high impulse rates.

A joint interspike interval difference stochastic spike train analysis: detecting local trends in the temporal firing patterns of single neurons.

We introduce a stochastic spike train analysis method called joint interspike interval difference (JISID) analysis. By design, this method detects changes in firing interspike intervals (ISIs), called local trends, within a 4-spike pattern in a spike train. This analysis classifies 4-spike patterns that have similar incremental changes. It characterizes the higher-order serial dependence in spike firing relative to changes in the firing history. Mathematically, this spike train analysis describes the statistical joint distribution of consecutive changes in ISIs, from which the serial dependence of the changes in higher-order intervals can be determined. It is similar to the joint interspike interval (JISI) analysis, except that the joint distribution of consecutive ISI differences (ISIDs) is quantified. The graphical location of points in the JISID scatter plot reveals the local trends in firing (i.e., monotonically increasing, monotonically decreasing, or transitional firing). The trajectory of these points in the serial-JISID plot traces the time evolution of these trends represented by a 5-spike pattern, while points in the JISID scatter plot represent trends of a 4-spike pattern. We provide complete theoretical interpretations of the JISID analysis. We also demonstrate that this method indeed identifies firing trends in both simulated spike trains and spike trains recorded from cultured neurons.

Noise effects on spike propagation in the stochastic Hodgkin-Huxley models

Effects of membrane current noise on spike propagation along a nerve fiber are studied. Additive current noise and channel noise are considered by using stochastic versions of the Hodgkin-Huxley model. The results of computer simulation show that the membrane noise causes considerable variation of the propagation time of a spike (thus changes in interspike intervals) for a small unmyelinated fiber of radius 0.1 approximately 1 micron.

The response of horseshoe crab lateral spine mechanoreceptors to slow ramp stimuli

The physiology of the mechanoreceptors associated with the lateral spines along the opisthosoma of the horseshoe crab were studied. Lateral spines were moved from one fixed position to another at constant speeds of from 2.5°/sec to 70°/sec and were held stationary at the new position after movement stopped. Receptor responses during spine movement and during the subsequent static stimulus were characterized. During spine movement at between 5 and 70°/sec the receptor response, measured either as the average spike frequency or as the number of spikes, was a linear function of the speed of spine movement. Detailed examination of the impulses generated during spine movement at constant speeds above 3.3°/sec showed that the interval between impulses (interspike interval) decreased as a log10 function of spine position. As the speed of spine movement was varied, the latency of the first and subsequent spikes (measured as degrees of spine movement before a given spike occurred) varied systematically in a manner which appeared dependent on the adaptation rate of individual receptors. Correction was made for conduction velocity. At higher speeds of spine movement the latency of the first spike decreased markedly for rapidly adapting receptors, but appeared to increase slightly for slowly adapting receptors. For slowly adapting receptors, the rate of adaption (change in interspike interval per unit time) during the static stimulus following a constant amplitude of spine movement increased slightly as the speed of movement was increased.

Changes in interspike interval during propagation: quantitative description.

The intervals between nerve impulses can change substantially during propagation because of conduction velocity aftereffects of previous impulse activity. Effects of such changes on interval histograms and on statistical parameters of spike trains were evaluated for Poisson spike trains and for trains generated by a clock with added random delays. The distribution of short intervals was significantly changed during propagation for these spike trains. Substantial changes in serial correlation coefficients were found in trains with certain initial interval distributions. The relevance of these effects to neural coding is discussed.

Patterned activity of the buccal ganglion of the nudibranch mollusc Archidoris pseudoargus.

Patterned activity of the buccal ganglion of the nudibranch mollusc Archidoris pseudoargus.