Interdischarge Intervals Research Articles

Temporal dynamics of triphasic waves and generalized periodic discharges (P10-1.012)

<h3>Objective:</h3> To quantitatively compare triphasic waves and generalized periodic discharges on scalp EEG. <h3>Background:</h3> Distinguishing epileptiform generalized periodic discharges (GPDs) and triphasic waves (TWs) can be challenging (Foreman <i>et al.</i>, 2016), and consequential since groups may benefit from anti-seizure medications differently. Discharge regularity is an important feature recapitulated in computational models of TWs (Song <i>et al.</i>, 2019) and GPDs (Ruijter <i>et al.</i>, 2017). Recent analysis of GPDs in patients after cardiac arrest have shown that regularity of GPD duration, morphology, and amplitude, based on visual scoring, portend worse prognoses (Nadjar <i>et al.</i>, 2022). This suggests that variability of discharges could be a quantifiable tool in distinguishing GPDs from TWs. <h3>Design/Methods:</h3> We retrospectively collected inpatient EEG recordings marked to show GPDs and TWs from Harborview Medical Center between 11/2020 and 5/2021. The best derivation of a 30 second artifact free period on average reference montage was low pass filtered (0–15hz) for analysis. After visually identifying discharges, interdischarge intervals (IDIs) were calculated based on maximal deflection of each discharge. For each EEG, variance of IDIs was normalized by median IDI, to calculate a regularity index (RI). RI of GPDs and TWs were compared with a one-tailed Wilcoxon rank sum test. <h3>Results:</h3> 24 EEGs with TWs and 33 EEGs with GPDs were studied. Median RI for TWs was 0.438 with a variance of 3.08. Median RI for GPDs was 0.368 with a variance of 4.31. Groups were not statistically different (<i>p</i>=0.08). Excluding EEGs of following cardiac arrest, 23 EEGs with TWs and 10 EEGs with GPDs were studied. Median RI of TWs was 0.430 with variance of 3.14. Median RI of GPDs was 3.14 with variance of 13.7. Groups were not statistically different (<i>p</i>=0.27). <h3>Conclusions:</h3> Comparison of normalized variability in IDI does not distinguish TWs from GPDs but may have utility in the context of other clinical data. <b>Disclosure:</b> Dr. Plummer has nothing to disclose. Dr. Raut has nothing to disclose. Dr. Brunton has received personal compensation for serving as an employee of University of Washington. The institution of Dr. Brunton has received research support from National Science Foundation . The institution of Dr. Brunton has received research support from Air Force Office of Scientific Research. The institution of Dr. Brunton has received research support from National Science Foundation. Dr. Hakimian has received personal compensation in the range of $500-$4,999 for serving as a Consultant for OptumRx. Dr. Hakimian has stock in Various.

The Relationship Between the Rhythmic Components of the Brain Electrical Activity During the Development of Status Epilepticus: An Operational Model of Brain Rhythms Generation.

Introduction: Despite the fact that brain rhythms are widely studied and officially classified, there is no consensus on their relationship, which can shed light on the genesis of rhythmic activity, its synchronization, functional role, and the formation of pathological reactions. Using the experimental status epilepticus (SE) as a model of brain in a hypersynchronized state with well-defined rhythms, we aimed to study the relationship between the rhythmic components of the brain electrical activity. Materials and Methods: Local field potentials (LFPs) were recorded simultaneously from the hippocampus, entorhinal cortex, medial septum, and amygdala during normal conditions and after kainic acid (KA) administration in waking guinea pigs. The dynamical spectral LFP properties were analyzed with the aid of Fast Fourier transform. Results: KA induces prominent SE with periodic combination of epileptiform discharge complexes and relatively quiet interdischarge intervals in the electrical activity of the brain. We have shown that new components appeared in the LFP spectra during the development of SE, representing a sequential doubling of the frequency, which had initially been dominating in the background records. Discussion: The phenomenon of frequency doubling can be interpreted as the octave principle of the LFP spectrum rhythmic carcass structure. The spectra of discharge complexes represent an alternation of harmonic spectra, where fundamental frequency coincides with one of the doubled frequencies dominating in the interdischarge activity. Using a nonlinear recurrent operation of rhythm multiplication and the obtained data we propose an operational model of the generation of rhythms and pathological discharges in the brain based on the octave principle.

A MULTIPLE MODEL ALGORITHM FOR ESTIMATING MOTOR UNIT FIRING PATTERN STATISTICS

The firing patterns and recruitment behavior of motor units (MUs) during a muscle contraction can be used in diagnosing neuromuscular disorder, studying motor control, improving the performance of electromyography (EMG) signal decomposition, and assessing the validity of MU potential trains extracted by an EMG decomposition algorithm. However, MU firing patterns extracted via EMG decomposition might contain several missed or erroneous that can lead to misleading conclusion. In this paper, we presented a multiple model estimation system (MMES) for estimating the mean ([Formula: see text]) and standard deviation ([Formula: see text]) of inter-discharge intervals (IDIs) of a MU. The presented MMES aggregates an existing error-filtered estimation (EFE) algorithm and a multiple linear regression model to estimate both [Formula: see text] and [Formula: see text]. The MMES estimates these two parameters using 10 features extracted from given IDIs and initial estimation of [Formula: see text] and [Formula: see text] values provided by EFE algorithm. Evaluation results using both simulated and real IDIs revealed that MMES performed better than EFE algorithm in estimating both [Formula: see text] and [Formula: see text] values in terms of root mean square error (RMSE), estimating variance and the range of estimated values. The RMSE values for MMES in estimating [Formula: see text] for simulated and real IDIs, respectively, were [Formula: see text] and [Formula: see text] that are statistically lower than that of EFE algorithm with RMSE [Formula: see text] and [Formula: see text]. In estimating [Formula: see text] in simulated and real IDIs, RMSE values of MMES, respectively were [Formula: see text] and [Formula: see text] that was significantly lower than those values obtained for EFE [Formula: see text] (for simulated IDIs) and [Formula: see text] (for real IDIs). More importantly, MMES outperformed EFE algorithm for real train with right-skewed IDI distribution. Consequently, MMES is more accurate, reliable and consistent than EFE algorithm for estimating IDI mean and standard deviation.

Evidence for mutual allocation of social attention through interactive signaling in a mormyrid weakly electric fish

Mormyrid weakly electric fish produce electric organ discharges (EODs) for active electrolocation and electrocommunication. These pulses are emitted with variable interdischarge intervals (IDIs) resulting in temporal discharge patterns and interactive signaling episodes with nearby conspecifics. However, unequivocal assignment of interactive signaling to a specific behavioral context has proven to be challenging. Using an ethorobotical approach, we confronted single individuals of weakly electric Mormyrus rume proboscirostris with a mobile fish robot capable of interacting both physically, on arbitrary trajectories, as well as electrically, by generating echo responses through playback of species-specific EODs, thus synchronizing signals with the fish. Interactive signaling by the fish was more pronounced in response to a dynamic echo playback generated by the robot than in response to playback of static random IDI sequences. Such synchronizations were particularly strong at a distance corresponding to the outer limit of active electrolocation, and when fish oriented toward the fish replica. We therefore argue that interactive signaling through echoing of a conspecific's EODs provides a simple mechanism by which weakly electric fish can specifically address nearby individuals during electrocommunication. Echoing may thus enable mormyrids to mutually allocate social attention and constitute a foundation for complex social behavior and relatively advanced cognitive abilities in a basal vertebrate lineage.

Statistical Characteristics of the Gaussian-Noise Spikes Exceeding the Specified Threshold as Applied to Discharges in a Thundercloud

We obtain expressions for the probabilities of the normal-noise spikes with the Gaussian correlation function and for the probability density of the inter-spike intervals. As distinct from the delta-correlated noise, in which the intervals are distributed by the exponential law, the probability of the subsequent spike depends on the previous spike and the interval-distribution law deviates from the exponential one for a finite noise-correlation time (frequency-bandwidth restriction). This deviation is the most pronounced for a low detection threshold. Similarity of the behaviors of the distributions of the inter-discharge intervals in a thundercloud and the noise spikes for the varying repetition rate of the discharges/spikes, which is determined by the ratio of the detection threshold to the root-mean-square value of noise, is observed. The results of this work can be useful for the quantitative description of the statistical characteristics of the noise spikes and studying the role of fluctuations for the discharge emergence in a thundercloud.

Electrocommununication in social groups of weakly electric fish: a comparison of Mormyrus rume and Marcusenius altisambesi (Mormyridae, Teleostei)

Event Abstract Back to Event Electrocommununication in social groups of weakly electric fish: a comparison of Mormyrus rume and Marcusenius altisambesi (Mormyridae, Teleostei) Kristina Gebhardt1, Miriam Böhme1 and Gerhard Von Der Emde1* 1 University of Bonn, Zoology, Germany African mormyrid fish generate and receive low-voltage electric signals (electric organ discharges, EODs) to sense nearby objects and for electrocommunication. With epidermal electroreceptors fish can perceive the highly stereotyped species-specific EOD waveforms of conspecifics, and thus can recognise each others presence and identity. In addition, Mormyrids can vary the inter-discharge intervals (IDIs) and create temporal situation dependent discharge patterns for electrocommunication. We investigated this special type of communication in two homogeneous groups of freely swimming weakly electric fish, Mormyrus rume (5 individuals) and Marcusenius altisambesi (4 individuals). Depending on the fishs’ positions in the experimental tank, it was possible to assign each recorded EOD to an individual sender. Thus, we could study the electrocommunication behaviour of every single group member in detail. During different situations like resting, foraging and aggressive encounters, we searched for behaviourally caused temporal patterns of IDIs between the fishes. The analysed sequences showed that both species performed complex situation-specific communication patterns, such as synchronised discharging, signalling in a fixed order or echo-responses between neighbours. By comparing the communication patterns of the two species, we found similarities, e.g. in fixed-order signalling, as well as differences, such as different IDI-patterns during resting or during aggressive encounters. For example during aggressive displays, M. rume showed extremely short IDIs that slowly increased in duration, a behaviour which was never found in M. altisambesi. Our results indicate that electrocommunication in group-living weakly electric fish plays an important role during social interactions and is highly complex. Keywords: electric organ discharges, electrocommunication, group living, interpulse interval, temporal pattern Conference: Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012. Presentation Type: Poster Presentation (see alternatives below as well) Topic: Communication Citation: Gebhardt K, Böhme M and Von Der Emde G (2012). Electrocommununication in social groups of weakly electric fish: a comparison of Mormyrus rume and Marcusenius altisambesi (Mormyridae, Teleostei). Conference Abstract: Tenth International Congress of Neuroethology. doi: 10.3389/conf.fnbeh.2012.27.00235 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 30 Apr 2012; Published Online: 07 Jul 2012. * Correspondence: Dr. Gerhard Von Der Emde, University of Bonn, Zoology, Bonn, 53115, Germany, vonderemde@uni-bonn.de Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Kristina Gebhardt Miriam Böhme Gerhard Von Der Emde Google Kristina Gebhardt Miriam Böhme Gerhard Von Der Emde Google Scholar Kristina Gebhardt Miriam Böhme Gerhard Von Der Emde PubMed Kristina Gebhardt Miriam Böhme Gerhard Von Der Emde Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Electric discharge patterns in group-living weakly electric fish, Mormyrus rume (Mormyridae, Teleostei)

Electrocommunication in weakly electric fish has various functions, such as species recognition and information transfer during social encounters. For communication, weakly electric fish rely on their electric organ discharges (EOD), which are generated by an electric organ located in the fish’s tail. While in mormyrids the species-specific EOD-waveform remains rather constant, the highly variable inter-discharge intervals (IDIs) enable the fish to modify their signalling behaviour on a short time scale. Different IDI-patterns were found to correlate with certain behavioural situations. We investigated electrocommunication in a social group of five freely swimming Mormyrus rume during different group behaviours. We found several electrical discharge patterns, which occurred during group foraging, aggressive encounters, fleeing and resting. We were able to describe several so far unknown signal patterns, such as synchronous discharging of two fish, and fixed-order-signalling in groups of up to five fish. Our results show that electrocommunication in social groups consists of complex and rapidly changing interactions between different individuals.

History dependence of human muscle-fiber conduction velocity during voluntary isometric contractions

The conduction velocity (CV) of a muscle fiber is affected by the fiber's discharge history going back ∼1 s. We investigated this dependence by measuring CV fluctuations during voluntary isometric contractions of the human brachioradialis muscle. We recorded electromyogram (EMG) signals simultaneously from multiple intramuscular electrodes, identified potentials belonging to the same motor unit using EMG decomposition, and estimated the CV of each discharge from the interpotential interval. In 12 of 14 subjects, CV increased by ∼10% during the first second after recruitment and then fluctuated by about ±2% in a way that mirrored the fluctuations in the instantaneous firing rate. The CV profile could be precisely described in terms of the discharge history by a simple mathematical model. In the other two subjects, and one subject retested after cooling the arm, the CV fluctuations were inversely correlated with instantaneous firing rate. In all subjects, CV was additionally affected by very short interdischarge intervals (<25 ms): it was increased in doublets at recruitment, but decreased in doublets during continuous firing and after short interdischarge intervals in doubly innervated fibers. CV also exhibited a slow trend of about -0.05%/s that did not depend on the immediate discharge history. We suggest that measurements of CV fluctuations during voluntary contractions, or during stimulation protocols that involve longer and more complex stimulation patterns than are currently being used, may provide a sensitive approach for estimating the dynamic characteristics of ion channels in the human muscle-fiber membrane.

Novel electrosensory advertising during diurnal resting period in male snoutfish, Marcusenius altisambesi (Mormyridae, Teleostei)

During the day, weakly electric snoutfish, such as Marcusenius altisambesi from the Okavango delta, avoid visually oriented predators by hiding in sheltered, dark places where they discharge their electric organs at a low and variable rate, interspersed with occasional short bursts (mean discharge rate, 4–12 Hz). Hence, histograms of inter-discharge intervals (IDI) are broad and bimodal (IDI range, about 15–500 ms; “variable IDI pattern”). We report here that with a female neighbor in electrical communication reach, captive males of M. altisambesi (N = 4) each showed a novel type of IDI resting pattern that was characterized by a higher and more constant discharge rate (16–28 Hz). These IDI histograms were unimodal and narrow (IDI range, about 11–100 ms; “regularized IDI pattern”). In each of these males, the regularized pattern vanished when the female neighbors were replaced by males, and the common variable IDI pattern of low rate was observed instead. In an unforced choice paradigm, six M. altisambesi experimental females were allowed to choose between two electric fish decoys, one playing back the novel regularized IDI pattern and one playing back the variable IDI pattern. Five experimental females significantly preferred staying close to the decoy playing back the regularized IDI pattern, whereas one female showed the opposite preference. It appears that males advertise to females during their diurnal period of overt inactivity, with an inconspicuous signal that neither threatens conspecifics nor alerts predators by overt behavior. A secondary function of the regularized male IDI pattern could be to advance the reproductive cycle of females.

Period doubling bifurcation in a train of spontaneous activity

Introduction: It has been shown that fibrillations (FIBs) and positive sharp waves (PSWs) occur during spontaneous oscillations of the membrane potential when the threshold is reached. According to the models of excitable membranes these oscillations should be nonlinear. We wondered whether the nonlinearity of the underlying process could also be demonstrated indirectly in the pattern of spontaneous discharges that can be recorded much easier extracellularly in routine electromyography. A simple example of nonlinear behaviour is a period doubling bifurcation in a periodic system. Methods: In our clinical neurophysiology laboratory discharges are saved on hard disc and the interval between successive discharges is analyzed if there is any doubt whether the discharges occur at regular intervals. In one recording out of 32 we found a phenomenon that we believe to represent a bifurcation. The recording is from the left anterior tibial muscle of a 67 year old patient. The patient showed widespread presence of spontaneous activity and fasciculations in muscles. Neurography was normal. Thus, a motor neuron disease was suspected. The recordings were made with the commercial Neurophysiology workstation „Keypoint“ from ALPINE Biomed with concentric needle electrodes. The samples were exported in ASCII format at a sampling frequency of 24kHz and a resolution of 1µV. Discharges were selected manually and the interdischarge interval (IDI) was calculated. Results: The upper trace in Fig.1 shows the signal as recorded with the concentric needle electrode. The peaks of the discharges that were used to calculate the interdischarge intervals are marked with little circles. The lower trace shows the interdischarge intervals as a function of time. Note that the discharge intervals decrease initially, and increase slowly afterward. At the moment indicated by the double arrow two different IDIs occur that alternate. This resembles behaviour resembles very closely period doubling bifurcations that can be observed in simple nonlinear systems such as the logistic map. Discussion: The recording presented here illustrates that irregularity at the end of trains of spontaneous activity can be the result of nonlinear deterministic behaviour. Further studies have to show whether more irregular behaviour that also can be observed at the end of these trains can also be described with methods of nonlinear dynamics.

Electric signalling and reproductive behaviour in a mormyrid fish, the bulldog Marcusenius macrolepidotus (South African form)

Bulldog fish (Marcusenius macrolepidotus) generate short (<1 ms) electric-organ discharges (EODs), separated by much longer and highly variable interdischarge intervals (IDIs). We observed overt behaviour and electrical activity during reproductive behaviour in a male and in a female bulldog, and identified IDI patterns with putative signal functions. In contrast to Pollimyrus adspersus and Pollimyrus isidori, in which an elaborate and extended courtship precedes spawning proper, our fish started spawning almost immediately when we allowed the female to enter the male’s territory. The male did not construct a nest, and neither parent provided parental care. The male showed very little aggression towards the intruding female. Fish spawned in bouts near the male’s hiding place, and eggs were scattered by the female’s vigorous tail flips as she left the spawning site, only to return shortly thereafter. During spawning bouts, both fish generated highly stereotyped IDI patterns: the male generated a series of IDIs gradually decreasing from about 200 ms to about 55 ms that was abruptly terminated by a long IDI. The female generated a series of relatively regular IDIs (about 54 ms) that was followed by a marked increase in IDI duration (the probable time of spawning). Finally, a sharp decrease in IDIs to about 20 ms accompanied the female’s sudden escape from the spawning site. In between spawning bouts, both fish generated series of very short IDIs (high discharge rate, HD) that alternated abruptly with very low-rate inter-HD activity (especially in the male). IDIs as short as 9 ms (male) or 11 ms (female) occurred during HD displays. No visible aggression, in fact very little overt behaviour, occurred during these HD displays in both fish. Agonistic interactions between male and female, outside a reproductive context, were similar to those previously described in male pairs, including overt behavioural patterns such as parallel swimming, antiparallel display and attack, as well as HD displays. When not interacting, fish did not generate HD displays. We suggest the HD display is a communication signal in both reproductive and agonistic contexts.

Intraspecific agonistic interactions in freely swimming mormyrid fish, Marcusenius macrolepidotus (South African form)

South African bulldogs (Marcusenius macrolepidotus, Mormyridae) generate brief (less than 1 ms) electric organ discharges (EODs), separated by much longer and highly variable inter-discharge intervals (IDIs). The diurnal and nocturnal overt behaviour and electrical activity were studied under various conditions: in isolated fish, in pairs of fish, and in a group of four fish that were kept in a “natural” large aquarium. EODs from up to four individuals were recorded simultaneously and identified. While resting during the day, isolated fish showed a broad inter-individual variability of IDI patterns, with distribution histogram modes ranging from 85.7 ms to 325.8 ms. When foraging during the day, IDI modes were shorter and less variable (36.3–48.3 ms). Behaviour patterns displayed during nocturnal agonistic encounters were retreating, parallel swimming, anti-parallel display, attack, and fleeing/chasing. High-discharge-rate (HD) displays were observed at several stages of these encounters, for example, during antiparallel display (a period of low overt motor activity), or following attacks. IDI durations as short as 11 ms occurred during HD displays, which followed low-rate inter-HD activity almost without transition. IDI distribution histogram modes when fish showed anti-parallel display were 15.4 ms and 24.8 ms, and 30.0 ms during nocturnal nonagonistic interactions. No overt fighting was observed once a dominance relationship was established. In a large aquarium, an approaching dominant male evoked a simultaneous discharge arrest in a group of three subdominant males.

Dynamical behavior of a pacemaker neuron model with fixed delay stimulation.

In physiological and pathological conditions, many biological oscillators, such as pacemaker cells, operate under the influence of feedbacks. Fixed delay stimulation is a standard preparation to evaluate the effects of such influences. Through the study of the Hodgkin-Huxley model, we show that such recurrent excitation can lead to regular and irregular discharge trains with interdischarge intervals that are up to several multiples of the period of the oscillator. In other words, we show that recurrent excitation can considerably slow down the firings of the pacemaker. This result contrasts with previous studies of similar preparations that have reported that fixed delay stimulation leads to a bursting pattern in which regimes of high-frequency firing alternate with periods of quiescence. We elucidate the mechanisms underlying the behavior of the oscillator under fixed delay perturbation through the analysis of the dynamics of a well-known two-dimensional oscillator, namely, the Poincaré oscillator.

Variability of the electric organ discharge interval duration in resting Gymnotus carapo.

We recorded the electric organ discharges of resting Gymnotus carapo specimens. We analyzed the time series formed by the sequence of interdischarge intervals. Nonlinear prediction, false nearest neighbor analyses, and comparison between the performance of nonlinear and linear autoregressive models fitted to the data indicated that nonlinear correlations between intervals were absent, or were present to a minor extent only. Following these analyses, we showed that linear autoregressive models with combined Gaussian and shot noise reproduced the variability and correlations of the resting discharge pattern. We discuss the implications of our findings for the mechanisms underlying the timing of electric organ discharge generation. We also argue that autoregressive models can be used to evaluate the changes arising during a wide variety of behaviors, such as the modification in the discharge intervals during interaction between fish pairs.

Development of electrical signalling in larvae of the African fish, Pollimyrus adspersus (Mormyridae, Teleostei): the patterns of interdischarge intervals

The ontogenetic development of the overt motor and the electrical signalling behaviour in larvae of a West African elephantfish, Pollimyrus adspersus, were studied. At an age of 35–40 days, hovering in mid‐water was first observed. Before that time, the larvae moved only occasionally and rested in the nest that was guarded by the male parent. The very low electric organ discharge (EOD) rate of 2.4 ± 0.9 Hz observed in 8‐ to 10‐day‐old larvae (that generate their first EODs on day 8) increased to an adult rate of 8.4 ± 1.7 Hz in 21‐ to 25‐day‐old larvae. Even 8‐ to 10‐day‐old larvae generated a trimodal inter‐EOD interval distribution (with three distinct discharge rates), similar to that observed in adults, although larval interval modes were of much longer duration. For the first (high rate) mode, the trend towards shortening stabilized already at the age of 21–25 days, whereas for the second and third (low rate) modes, this occurred only at an age of around 61–70 days.Inter‐EOD interval patterns recorded during swimming behaviour of 8‐ to 10‐day‐old larvae closely resembled that observed in juveniles (exceeding 100 days): there was a single mode only, and EOD rate was increased (13.1 ± 3.2 Hz).Artificial stimulation with natural inter‐EOD interval patterns previously recorded from other larvae or the nest‐guarding male did not evoke any responses in 14‐day‐old larvae, apart from a brief EOD stop response to stimulus onset. However, even in larvae as young as 11 days, Preferred Latency Responses of their EODs to an artificial series of stimulus pulses (constant rate of 5 Hz) were observed at a stimulus intensity of 120 μVp‐p/cm. In the youngest larvae, 36‐ms latencies were most frequent; this shortened to 19 ms in 31‐day‐old larvae (approaching the adult value; Kramer, 1978). The time pattern of EOD generation in P. adspersus larvae resembled that in mature specimens even before the adult electric organ became functional.

Species recognition by the sequence of discharge intervals in weakly electric fishes of the genus Campylomormyrus (Mormyridae, Teleostei)

Abstract. In two Campylomormyrus species, tamandua and rhynchophorus from Central Africa, the electric organ discharge (EOD) activity was studied during the nocturnal activity phase in the laboratory. Both species have a pulse-type EOD of less than 200 μs duration and similar waveform; the sequence of inter-discharge intervals, however, differed characteristically: C. tamandua displayed a 'micro-pattern' encompassing nearly the whole range of intervals in a sequence of only three intervals (long-intermediate-short), while in C. rhynchophorus adjacent intervals tended to be more similar in duration. Four C. rhynchophorus and five C. tamandua were tested for their preference of conspecific pulse sequences rather than those of the other species, respectively, in playback experiments. These were performed in a T-maze paradigm such that two pulse patterns, one from each species, were simultaneously presented via two electric fish dipole models. Two pulse sequences recorded from different individuals were used to represent each species; the natural EOD waveform was replaced by a square-wave pulse of approximately natural duration. The pattern pairings and the sequence of stimulus patterns followed a randomized blocks design. Each of the four C. rhynchophorus had significantly higher preference scores for the conspecific pulse patterns than for those of C. tamandua, while in C. tamandua no such discrimination was observed. It is suggested that the juvenile C. tamandua used would probably have joined mixed-species schools as reported to exist in the wild, while this appears unlikely in the more mature C. rhynchophorus. One of the functions of the inter-discharge interval code of communication in mormyrids is species recognition although this may be seen only in sufficiently mature fish.

Discharge properties of single motor units in patients with spinal cord injuries

To study neurophysiological correlates of spastic paresis, we analyzed the discharge pattern of single motor units (SMUs) during sustained voluntary contraction from muscles weakened by spinal cord injury (SCI) and from muscles of near normal strength just at or above the level of injury. The average firing rate of SMUs was reduced in patients' biceps brachii and tibialis anterior muscles compared with controls, but not in the triceps brachii. Floating serial correlation coefficients obtained from successive interdischarge intervals were significantly more positive in patients than in controls in all three muscles. One statistical measure of regularity of discharge, akin to a coefficient of variation, was best able to differentiate patient and control SMUs. Increased discharge variability in muscles just above the level of injury suggested that subtle effects of traumatic SCIs were more extended than was clinically apparent. Although consistent statistical differences could be measured, these changes were not specific to SCI, nor were all SMUs equally affected.

Mechanical implications of paired motor unit discharges in pathological and voluntary tremor

Paired motor unit discharges (PDs), i.e., two discharges of the same motor unit (MU) with short interval, and their relation to tremor amplitude were studied in the first dorsal interosseous muscle (FDI) of patients with parkinsonian or essential tremor and in normal subjects mimicking tremor. In both pathological and voluntary tremor, interdischarge intervals of PDs were inversely correlated with the amplitude of the subsequent tremor beat, i.e., PDs with shorter intervals were followed by higher tremor beats. To further assess their mechanical impact, PDs were simulated by applying paired stimuli to MUs of the FDI in normal subjects using intramuscular microstimulation. Following paired stimuli, summation of twitch responses was more than linear. This was also the case with the paired stimuli applied at a tremor-like repetition rate (5 Hz). These findings stress the importance of PDs for tremor expression.

Single-fibre electromyography with a personal computer.

A single-fibre electromyography measuring unit based upon a personal computer (Apple II) and a special triggering unit is described. Its compact size facilitates its use online, next to the patient. It is a relatively cheap system, and can be handled by one investigator and a nurse. Operation is simple, and error messages are provided. Investigation of a patient consists of measuring the time of occurrence of action potentials in up to 20 trains of complex motor unit action potentials (MUAPs). One train may consist of up to 170 MUAPs, each comprising a maximum of four single action potentials (spikes). Triggering is performed with a special unit after an initial spike, triggering at an adjustable level is only possible within an adjustable time window. This feature reduces false triggerings and allows selection of a part of a complex MUAP. Interval analysis by the computer also reduces processing of MUAPs originating from other motor units. Computed are the mean consecutive difference (MCD) values of the jitter, the variance, the percentage of blockings and the number of relevant intervals. Scatter plots can be displayed and printed of the raw data, the consecutive differences or the interpulse intervals (IPI) against the interdischarge intervals (IDI). Suspicious data may be rejected by manipulation of graphical cursors. If a MUAP consists of at least four spikes, a test can be carried out whether there is a neurogenic variability cause concomitant jitter. The system has been evaluated over the last two years in the EMG department of the Academic Hospital, Utrecht, The Netherlands.

Bizarre repetitive discharges recorded with single fibre EMG.

Single fibre EMG was used to record bizarre repetitive discharges in patients with chronic denervation or muscle disorders. The low variability of intervals between individual spike components on successive discharges suggests that the bizarre repetitive discharges are based on ephaptic impulse transmission from the muscle fibre starting the discharge (principal pacemaker) to the adjacent muscle fibres. The low variability of the interdischarge intervals is explained by ephaptic reactivation of the principal pacemaker by one of the fibres participating in the previous discharge (a co-pacemaker). Secondary activator fibres may spread activity to more fibres. The bizarre repetitive discharge stops when either the principal pacemaker or the co-pacemaker become sufficiently subnormal to block. The co-pacemaker may be missing in cases of low frequency bizarre repetitive discharges, particularly in those with irregular interdischarge intervals.