Spike Train Patterns Research Articles

Use of a spiking neural model to simulate lip motor unit activity and movements in speech

In order to clarify the nature of EMG‐kinematic relationships involved in speech production, a rudimentary computer model of the lower lip as a neuromechanical system was developed. The model consists of three muscles having forcing functions that act on a common point. Each muscle is treated as a set of single motor units with associated motoneuron spike activity and muscle‐unit twitch forces. The temporal patterns of motoneuron spike trains, which serve as the system input, are based on single motor unit EMG recordings obtained during syllable repetition [M. McClean and J. Clay, Society for Neuroscience Abstracts 19, 229.15 (1993)]. System output is evaluated in terms of lower‐lip movement through the midsagittal plane. Simulations produce realistic movement patterns when they are constrained by reasonable assumptions about motor unit intrinsic properties, muscle force angles, and relative timing of motoneuron spike trains. Initial applications of the model have focused on the mechanisms of speech rate control. Different rates of syllable production are established by the overall temporal patterns of motoneuron spike trains, and the effects of varying system parameters are evaluated at each rate.

The algorithmic complexity of neural spike trains increases during focal seizures

The interspike interval spike trains of spontaneously active cortical neurons can display nonrandom internal structure. The degree of nonrandom structure can be quantified and was found to decrease during focal epileptic seizures. Greater statistical discrimination between the two physiological conditions (normal vs seizure) was obtained with measurements of context-free grammar complexity than by measures of the distribution of the interspike intervals such as the mean interval, its standard deviation, skewness, or kurtosis. An examination of fixed epoch data sets showed that two factors contribute to the complexity: the firing rate and the internal structure of the spike train. However, calculations with randomly shuffled surrogates of the original data sets showed that the complexity is not completely determined by the firing rate. The sequence-sensitive structure of the spike train is a significant contributor. By combining complexity measurements with statistically related surrogate data sets, it is possible to classify neurons according to the dynamical structure of their spike trains. This classification could not have been made on the basis of conventional distribution-determined measures. Computations with more sophisticated kinds of surrogate data show that the structure observed using complexity measures cannot be attributed to linearly correlated noise or to linearly correlated noise transformed by a static monotonic nonlinearity. The patterns in spike trains appear to reflect genuine nonlinear structure. The limitations of these results are also discussed. The results presented in this article do not, of themselves, establish the presence of a fine-structure encoding of neural information.

Properties of favored patterns in spontaneous spike trains and responses of favored patterns to electroacupuncture in evoked trains

By using ‘the modified detection method’, our previous study has shown that all spontaneous spike trains recorded from several areas of brain and spinal cord have favored patterns (FPs). The present study further shows that: (1) all newly detected spike trains from substantia nigra zona compacta, nucleus periventricularis hypothalami and nucleus hypothalamicus posterior also have FPs, and some spike trains from neurons in the same nucleus have a common favored pattern (CF, i.e. they share the same FP), indicating that FP and CF in spike trains are common phenomena; (2) all serial correlation coefficients of FP repetitions (in serial order) in different spike trains detected are less than 0.3 (close to 0), revealing that the repetition of FPs is a renewal process; (3) in different periods of the spike trains evoked by electroacupuncture (EA), the number of different FPs and the number of repetitions of the same representative FP either increase or decrease along with the change of firing rate. The tendencies of these changes are very similar, but after EA the repetitions of different FPs in the same spike trains change differently, showing that different (hidden) responses exist at the same time. The above results suggest that the FPs in spike trains may represent various neural codes, and ‘the modified detection method of FP’ can pick up more information from spike trains than the firing rate analysis, hence it is a very useful tool for the study of neural coding.

Favored patterns in spontaneous spike trains

By using the modified detection method, favored patterns can be detected in a total of 44 spontaneous spike trains. Among these the ‘periodical burst’ discharge of one sympathetic preganglionic neuron and the ‘fast-slow’ alternative discharge of some hypothalamic neurons have visible characteristics, hence we use them to test the reliability of our method by comparing the detected patterns with the non-sequential interval histograms and oscillograms of the spike trains. The comparisons show that our method is reliable. The spike trains of nucleus raphe magnus (NRM) and the locus coeruleus (LC) have no visible characteristics; from these the following results have been observed: (1) all spike trains have one or more favored patterns; (2) some spike trains from neurons in the same nucleus have common fragments of favored patterns; (3) the favored patterns in spike trains recorded from different nuclei are different from each other; (4) some favored patterns in spike trains of the NRM neurons remain unchanged from beginning to end in 35-min records and their repetitions are relatively stable; and (5) microinjection of normal saline or normal serum into the LC has no significant influence on the occurrence of favored patterns in 35-min records of spike trains of the LC neurons. The above results indicate that the favored patterns in spike trains are objective and regular phenomena with relative stability. It seems likely that favored pattern may be used (as an index of the neuronal activity) in combination with the microinjection technique, etc., for various studies including studies on neural coding.

The effect of muscle length on motor unit discharge characteristics in human tibialis anterior muscle

Muscle length influences the contractile properties of muscle in that when muscle is lengthened the relaxation phase of the muscle twitch is prolonged and when muscle is shortened, the relaxation phase is shorter in duration. As a result, the force exerted by active motor units varies with muscle length during voluntary contractions. To determine if motoneuron spike trains were adjusted to accommodate for changes in the contractile properties imposed by shortened and lengthened muscle, motor unit action potentials were recorded from the tibialis anterior muscle at different muscle lengths. Twenty subjects performed isometric ramp contractions at ankle angles of 20 degrees dorsiflexion, neutral between dorsiflexion and plantar flexion, and 30 degrees plantar flexion, which put the tibialis anterior muscle in a shortened, neutral, or lengthened condition, respectively. During isometric contractions where torque increased at 5% MVC/s, motor unit discharge rate at recruitment was greater in shortened muscle than in lengthened muscle (P less than 0.05). Brief initial interspike intervals (less than 40 ms) occurred more frequently in shortened muscle than in either neutral length or lengthened muscle. During steady contractions, motor unit discharge rate was greater per unit torque (N.m) in shortened muscle than in neutral length or lengthened muscle (P less than 0.05). These findings indicate that muscle length does influence the discharge pattern of motor unit spike trains during isometric ramp contractions.(ABSTRACT TRUNCATED AT 250 WORDS)

Recurring discharge patterns in multiple spike trains

We present a procedure to detect recurring discharge patterns in multiple spike trains. Such recurring patterns can include many spikes and involve from three to many spike trains. The pattern detection procedure is based on calculating the exact probability of randomly obtaining each individually recurring pattern. The statistical evaluation is based on the use of 2 x 2 contingency tables and the application of Fisher's exact test. Several simulations are applied to evaluate the method. Findings based on applying the procedure to simultaneously recorded spike and event trains are described in a companion paper (Frostig et al. 1990).

Recurring discharge patterns in multiple spike trains

Simultaneously recorded spike trains were obtained using microwire bundles from unrestrained, drug-free cats during different sleep-waking states in forebrain areas associated with cardiac and respiratory activity. Cardiac and respiratory activity was simultaneously recorded with the spike trains. We applied the recurring discharge patterns detection procedure described in a companion paper (Frostig et al. 1990) to the spike and cardiorespiratory trains. The pattern detection procedure was applied to detect only precise (in time and structure) recurring patterns. Recurring discharge patterns were detected in all simultaneously recorded groups. Recurring discharge patterns were composed of up to ten spikes per pattern and involved up to four simultaneously recorded spike trains. Fourty-two percent of the recurring patterns contained cardiac and/or respiratory events in addition to neuronal spikes. When patterns were compared over different sleep-waking states it was found the the same units produced different patterns in different states, that patterns were significantly more compact in time during quiet sleep, and that changes in the discharge rates accompanying changes in sleep-waking states were not correlated with changes in pattern rate.

A model proposing synaptic and extra-synaptic influences on the responses of cochlear nerve fibres

A unique property of sensory coding in the vertebrate auditory system is the existence of the classical form of excitatory centre-inhibitory surround in relative spike rate along the stimulus frequency dimension, in addition to a representation of temporal fine structure of high frequency periodic stimuli in the discharge pattern of primary afferent spike trains. We present a model which designates three factors that influence rate and temporal synchrony in spike responses; an excitatory factor, a suppressive factor and a synchronizing factor. The model proposes that an essential integration of bioelectric signals occurs in the primary afferent fibre. It is presumed that mean spike rate depends on mean level of membrane depolarization and synchronization depends on periodic modulation of membrane potential at the spike initiating zone. In the model, the excitatory factor is synaptically-mediated, excitatory post-synaptic potential (e.p.s.p.); the suppressive factor is negative DC polarization of the fibre membrane and the synchronizing factor is AC modulation of the fibre membrane potential. It is proposed that both the negatively-polarizing and high-frequency modulating signals are derived from extracellular current flow in the cochlea.

Background firing in cortical neurons with blockade of synaptic inhibition in guinea pig neocortical slices maintained in vitro

The effects of 100 µM picrotoxin on neuronal background firing were investigated in guinea pig neocortical slices maintained in vitro. Picrotoxin or bicuculline application is known to bring about an abrupt increase in background firing or the onset of spontaneous epileptiform volleys at a higher excitatory and inhibitory level in the in vivo than in the in vitro cortex. Blocking GABA-ergic inhibition hardly affected the pattern of background spike trains, although stimuli-induced response did become epileptiform. Findings from this research would thus indicate that any inhibitory processes taking place during in vitro background activity are only very slight and exert no significant effect on this activity.

A method for determining the primary effect of a stimulus in tonically firing neurons using spike train analysis

We present a novel method for measuring changes in the timing of spikes evoked by a stimulus in single neurons. The result provides an unambiguous separation of the stimulus effect from effects due to intrinsic spike train patterns. This separation facilitates the comparison of responses in different neurons. The analysis is based only on the spike train and requires no models of the underlying cell behavior.

Evidence on precise time-coded symbols and memory of patterns in monkey cortical neuronal spike trains.

High-resolution examination of pulse sequences generated by single visual cortex cells of the rhesus monkey in response to precisely controlled visual stimuli has disclosed (i) that the outputs of such neurons contain highly improbable (P less than 10(-7) numbers of identical triplets of precisely repeating pulse patterns; (ii) that the precision of such matches is better than 1/6000th of a second; (iii) that there is a similarly improbable high number of precisely matching pairs of triplets and anti-triplets, about half of which are present in symmetrical quadruplets of the form A-B-A, and that precisely replicating quadruplets and quintuplets are similarly generated in improbably large numbers; (iv) that identical triplets occur highly preferentially during immediately succeeding presentation of the same stimulus to the eye; and (v) that identical triplet (and doublet) patterns occur much more frequently in the responses of the same nerve when the eye receives identical or similar stimuli in different experiments than when dissimilar stimuli are applied. From these findings it is concluded (i) that the high precision of pattern replication required for triplets of pulses in time to serve to encode specific inputs and to permit their decoding through spatial summation is met (observations i-iii); (ii) that stimulus-specific triplets symbolize components of responses to specific stimuli (observation iv); (iii) that a temporary memory store of previous responses exists (observations iv and v); and (iv) that the mammalian brain uses precise patterns of discharges in time to represent and store specific data, rather than statistical qualities associated with pulse trains to symbolize qualitative stimulus components.

Warm-Up and Stridulation in the Buschcricket, Hexacentrus Unicolor Serville (Orthoptera, Conocephalidae, Listroscelidinae)

ABSTRACT The morphology of the stridulatory organ of the tropical bushcricket Hexacentrus unicolor is described and an investigation is made of stridulatory movements and muscle activities. The song is produced by extremely fast stridulatory movements (320-415 Hz), during which, while closing the wings, a highly specialized file is brought into contact with the plectrum to produce sound. The muscles are activated with the same frequency, i.e. they work synchronously (neurogenic). A few minutes before the stridulation starts, the muscles are activated in a similar rhythm to that pertaining during singing (pattern of spike trains and pauses). As a result, the thorax temperature increases considerably (up to approximately 37°C, 13-15°C higher than the ambient temperature). The frequency of the muscle potentials within the spike trains rises during warm-up. There are, however, indications that no phase displacement of antagonistically working muscles takes place.

Sleep and purposive behavior: Inverse deviations from randomness of neuronal firing patterns in the feline thalamus: A new form of homeostasis?

In behaving cats trained to press a bar for small aliquots of milk reward, single neuronal firing patterns were monitored from the nucleus reticularis (NR) thalami during bar bressing (BP), subsequent quiet wakefulness with EEG spindles (S- QW ), grooming behavior (GR) and slow-wave sleep (SWS). The temporal patterns in the neuronal spike trains were analyzed using a non-parametric method based on relative relations between sequential spike intervals. The deviations of pattern occurrences from the random model were quantified. During BP, specific patterns occurred much more often while others occurred much less often than predicted by the random model. Patterns that were dominant during BP, were selectively suppressed or virtually eliminated during S- QW , GR and SWS, despite the increased firing rate; and, vice versa, patterns that were suppressed below chance level during BP, became dominant during S- QW , GR and SWS. The magnitudes of these inversions of the statistical distribution of patterns were not random but graded and positively correlated, thus indicating that they were homeostatically controlled. Since the inversions were already evident shortly after the satiated ceased bar pressing, they may be related to the 'need' for sleep. On the basis of the known mechanisms of pattern generation and changes in receptors for putative transmitters, it was postulated that the inversions of pattern distribution are related to the recuperative function of SWS, i.e. resensitization of receptors that had been desensitized during the animal's stereotypic BP performance. The NR and other neuronal ensembles seem to constitute an oscillatory system with two modes of reciprocal connectivities : one is supporting wakefulness and emission of specific firing patterns, and the other is incompatible with wakefulness and instead is associated with inversion of statistical distribution of firing patterns and recuperative function of SWS.

Favored patterns in spike trains. I. Detection.

Traditional spike-train analysis methods cannot identify patterns of firing that occur frequently but at arbitrary times. It is appropriate to search for recurring patterns because such patterns could be used for information transfer. In this paper, we present two methods for identifying "favored patterns" --patterns that occur more often than is reasonably expected at random. The quantized Monte Carlo method identifies and establishes significance for favored patterns whose detailed timing may vary but that do not have extra or missing spikes. The template method identifies favored patterns whose occurrences may have extra or missing spikes. This method is useful when employed after the results of the first method are known. Studies with simulated spike trains containing known interpolated patterns are used to establish the sensitivity and accuracy of the quantized Monte Carlo method. Certain trends with regard to parameters of the detected patterns and of the analysis methods are described. Application of these methods to neurophysiological data has shown that a large proportion of spike trains have favored patterns. These findings are described in the accompanying paper (3).

Favored patterns in spike trains. II. Application.

In this paper we apply the two methods described in the companion paper (4) to experimentally recorded spike trains from two preparations, the crayfish claw and the cat striate cortex. Neurons in the crayfish claw control system produced favored patterns in 23 of 30 spike trains under a variety of experimental conditions. Favored patterns generally consisted of 3-7 spikes and were found to be in excess by both quantized and template methods. Spike trains from area 17 of the lightly anesthetized cat showed favored patterns in 16 of 27 cases (in quantized form). Some patterns were also found to be favored in template form; these were not as abundant in the cat data as in the crayfish data. Most firing of the cat neurons occurred at times near stimulation, and the observed patterns may represent stimulus information. Favored patterns generally contained up to 7 spikes. No obvious correlations between identified neurons or experimental conditions and the generation of favored patterns were apparent from these data in either preparation. This work adds to the existing evidence that pattern codes are available for use by the nervous system. The potential biological significance of pattern codes is discussed.

The effect of the time pattern of presynaptic impulses on the transfer of information across an inhibitory synapse.

The effects of different time patterns in presynaptic spike trains on the transmission of information across an inhibitory synapse is examined in the muscle receptor organs of the crayfish abdomen. With regular input, the system would be strongly affected by phaselocking (Perkel et al. 1964), and it is shown that a similar phenomenon would occur during closedloop inhibitory feedback. The conditions under which different degrees of phase-locking occur is studied in simple models of the system, and the model predictions is compared with experimental observations of pre- and postsynaptic spike trains. The results suggest that phaselocking is uncommon during the normal operation of these sense organs, due to the special design of its neuronal elements, which promote irregular time patterns of impulse firing in both receptors and inhibitory neurons.

Neuronal firing patterns in the feline hippocampus during sleep and wakefulness

The study addressed the problem of information transmission in mammalian brain as reflected in the emergence or disappearence of temporal patterns in extra-cellularly monitored single action potentials from the dorsal hippocampus of unrestrained cats during slow wave sleep (SWS), rapid eye movement sleep (REM), and motionless quiet wakefulness (QW). The spike trains were analyzed with a non-paarametric technique. Chi-square statistics were used to measure deviations of firing patterns from the theoretical model which is based on the assumption that the intervals are random and/or independent from each other. The plots of the chi-square values for a given set of patterns represented the neuronal ‘signatures’ characteristic a behavioral state. During SWS most neurons followed the theoretical model, i.e. their ‘signatures’ were flat and statistically non-significant. However, during REM sleep and QW their firing modes showed specific deviations from the theoretical model: some patters occured more often while others less often than expected, thus generating large and statistically significant ‘signatures’. During REM sleep some neurons shared similar tendencies in their departures from the theoretical model. However, during QW the same neurons developed their individual ‘signatures’ which were significantly different from each other. Hence, the QW episodes were characterized by a greater differentiation of neuronal firing patterns. The mean firing rate and the shape of the time interval histogramwere not necessarily correlated with the emergence of specific temporal patterns in spike trains. The results suggest that information transmission from one neuron to anothe depends on the emergence of repetitive and specific temporal patterns. The strong tendency of most neurons to lapse during SWS into a firing mode that closely follows the theoretical model constitutes the basis for a working hypothesis which states that the essence of SWS recovery processes in cognitive systems is the disappearance of temporal patterns, and that the ‘noisy’ interactions between neurons plays an important role in the recuperative processes.

On statistical methods in neuronal spike-train analysis

Changes in membrane potential of a neuron are, under certain experimental conditions, manifested by spike discharges. The number of spikes recorded from the neuron within a given period represents the information which the neuron conveys; and the message, thus transmitted, is carried by the pattern of spikes and the intervals between spikes. This can be modeled by a stochastic point process. This article reviews in three parts recent developments of the statistical analysis of discharge patterns of spike trains recorded from individual nerve cells, and suggests several methods for identifying certain types of spike trains. The first part reviews those stochastic processes Y( t) used as models for the membrane potential changes. The occurence time of a spike is defined as a first-passage time of Y( t) upcrossing a threshold value. These upcrossing times form a point process describing the occurences of spikes. Evidently, the occurence rate depends on the underlying assumption of Y( t). Presently, a majority of the point process models adopt the renewal-process assumptions. The second part deals with statistical inferences on the models and the validation methods. The research in this area is scarce; the inference on renewal processes is based mostly on Cox and Lewis's book The Statistical Analysis of Series of Events. We have used the contiguity theory due to Le Cam [30] to derive several asymptotically optimal statistical procedures. The last part discusses some popular statistical techniques employed and some areas needed for further investigation.