Effect of prolonged refractoriness on the forward masking of tone bursts in single units of the mouse inferior colliculus

The estimation of conditional probability was used to demonstrate the effect of the postspike changes in neuron excitability on its response to the second burst in a pair with an interval between bursts ranging from 50 to 200 ms. The responses of the neurons of the inferior colliculus to pairs of low-intensity tone bursts were recorded extracellularly in anesthetized albino mice. The probability of the response to the second burst in a pair was estimated under two conditions: the presence and the absence of a spike in the response to the first burst. If the interval between burst was 50 ms, the probability of response was decreased in most neurons where there was a spike in the response to the first burst. The opposite trend was observed in a small proportion of neurons. If the interval was increased, it weakened the dependence of the response to the second burst on the character of the response to the first one. The suppression of inhibitory inputs by bicuculline emphasized the postspike refractoriness rather than canceled it. The possible mechanisms of the interdependence between the responses to two consecutive signals are discussed.     

Temporal interaction between single spikes and complex spike bursts in hippocampal pyramidal cells

Cortical pyramidal cells fire single spikes and complex spike bursts. However, neither the conditions necessary for triggering complex spikes, nor their computational function are well understood. CA1 pyramidal cell burst activity was examined in behaving rats. The fraction of bursts was not reliably higher in place field centers, but rather in places where discharge frequency was 6-7 Hz. Burst probability was lower and bursts were shorter after recent spiking activity than after prolonged periods of silence (100 ms-1 s). Burst initiation probability and burst length were correlated with extracellular spike amplitude and with intracellular action potential rising slope. We suggest that bursts may function as "conditional synchrony detectors," signaling strong afferent synchrony after neuronal silence, and that single spikes triggered by a weak input may suppress bursts evoked by a subsequent strong input.     

Nonlinear Relationships in the Patterns of Neuronal Spiking in Cortical Neurons

The pattern of neuronal spiking of cortical neurons was investigated in an awake nonimmobilized rabbit. Thecharacteristics of the interspike intervals (total numberof intervals, mean interval, mean-square deviation) and of the burst (group) activity (burst number, mean spikefrequency in a burst, mean spike number for a burst, meanburst duration) were considered. Nonlinear relationshipbetween the values of mean interspike intervals and thenumber of spike bursts was found. A number of functionswere applied to describe the observed phenomena. On thebasis of regression analysis two populations of corticalneurons with distinct neuronal spiking patterns wereidentified. Bursts occur at a higher rate in one populationthan the other, although both populations exhibit burstsand are otherwise indistinguishable.     

Measurement of electrical activity of long-term mammalian neuronal networks on semiconductor neurosensor chips and comparison with conventional microelectrode arrays

Based on complementary metal-oxide semiconductor (CMOS) technology a neurosensor chip with passive palladium electrodes was developed. The CMOS technology allows a high reproducibility of the sensors as well as miniaturization and the on-chip integration of electronics. Networks of primary neurones were taken from murine foetal spinal cord (day 14) and frontal cortex (day 15) tissues and cultured on the silicon surface in a chamber volume of 200 microl with 7 mm diameter. Measurements were performed between days 15 and 59 in vitro. Signals were recorded from both types of cultures. To test the capability of the system to detect pharmacologically induced activity changes two established neuromodulators were applied. The GABA(A)-receptor blocker bicuculline was applied to both tissue cultures, the glycine-receptor blocker strychnine to spinal cord cultures. Four network frequency parameters were analysed: spike rate (SR), burst rate (BR), frequency in bursts (FiB) and peak frequency in bursts (PFiB). Significant changes of spike rate and burst rate were measured with spinal cord cultures after bicuculline application. Significant changes of frequency in bursts and peak frequency in bursts were observed with frontal cortex cultures after bicuculline application. Significant changes of spike rate and frequency in bursts were recorded with spinal cord cultures after strychnine application. These results were compared with results achieved in the same laboratory by using glass-microelectrode arrays (MEAs). This comparison showed for spinal cord similar native spike and burst rate, but higher mean frequency and peak frequency in bursts, whereas frontal cortex activity had higher spike and burst rate and peak frequency in bursts. Application of bicuculline or strychnine to spinal cord networks showed stronger effects on MEAs, whereas with frontal cortex networks the modulation of activity was similar after application of bicuculline.     

Risk functions and expected spike density functions for neurons in the cat cochlear nucleus

The temporal properties of spontaneous and (or) evoked discharges of 157 neurons localized in dorsal cochlear nucleus of anaesthetized cats have been studied. Tone bursts were presented at stimulus best frequency in a free field from the side of ipsilateral ear. About half of cells were characterized by paused or build-up types of the discharge. For all such units a long lasting post-spike decrease in excitability could be seen from the analysis of hazard functions of spontaneous and evoked activity. As a result, the time dependence of conditional probability of the first crossing of the threshold (under condition of an absence of previous response spikes) or expecting probability function (EPF) were over the usual peristimulus histograms. Units with chopper discharges usually did not demonstrate alternative peaks in EPF. We interpreted this fact as evidence that chopper discharge pattern is a result of strong post spike decrease in excitability. Such pattern doesn't demonstrate an existence of real periodicity of the unit. In primary-like units the hazard functions demonstrated only minor after-spike decrease of excitability, and the EPFs were similar to the initial part of peristimulus histograms. Type II units (presumably inhibitory cells) were characterized by non-monotonous hazard functions and by a tendency to burst response patterns. In some cells, we observed a tendency to existence of real intrinsic oscillations both in the EPFs and hazard functions.     

Electrophysiology of "yellow cells," neurosecretory neurones in Lymnaea.

The thirty Yellow Cells of Lymnaea show single, double and other extra spike modes of firing. Yellow Cell bursts consist of various combinations of single, doublet and triplet spikes whose number per burst varies spontaneously. Single spike firing modes of activity can be converted into doublets or bursts (and vice versa) by applying steady currents of the appropriate polarity. Spike activity is basically endogenous although it is modulated by low frequency synaptic input originating from within the brain. Interburst interval is affected by the number of spikes occurring in the preceding burst. This varies spontaneously or can be induced by applying appropriately timed current pulses or occurs following synaptic input. Excitatory synaptic input often induces bursts which far exceed the duration of the input and which are followed by long periods of inhibition.     

Selectivity of stimulus induced responses in cultured hippocampal networks on microelectrode arrays

Sensory information can be encoded using the average firing rate and spike occurrence times in neuronal network responses to external stimuli. Decoding or retrieving stimulus characteristics from the response pattern generally implies that the corresponding neural network has a selective response to various input signals. The role of various spiking activity characteristics (e.g., spike rate and precise spike timing) for basic information processing was widely investigated on the level of neural populations but gave inconsistent evidence for particular mechanisms. Multisite electrophysiology of cultured neural networks grown on microelectrode arrays is a recently developed tool and currently an active research area. In this study, we analyzed the stimulus responses represented by network-wide bursts evoked from various spatial locations (electrodes). We found that the response characteristics, such as the burst initiation time and the spike rate, can be used to retrieve information about the stimulus location. The best selectivity in the response spiking pattern could be found for a small subpopulation of neurones (electrodes) at relatively short post-stimulus intervals. Such intervals were unique for each culture due to the non-uniform organization of the functional connectivity in the network during spontaneous development.     

基于最大锋电位间隔的爆发检测自适应算法

在各种类型的培养神经元网络、哺乳动物中枢神经系统和切片中,都可以观察到爆发。爆发是空间-时间放电模式的重要特征,它由一系列高频率发放的连续动作电位组成,由于在时间尺度上的复杂性,使其辨识和探测存在许多困难。自适应算法利用爆发外部锋电位间隔超过爆发内部锋电位间隔的累加和识别爆发本身。基于该算法原理,以爆发内部最大锋电位间隔参数作为确定爆发的约束条件,改进爆发检测自适应算法。实验结果表明,改进算法可以有效地避免爆发的漏检和错检,较准确地检测出神经元的爆发活动,确定爆发活动的数目和持续时间等,爆发检测的平均准确率为93.8%,比原自适应算法提高了35.3%。     

Physiological properties of sympathetic preganglionic neurones in the thoracic intermediolateral nucleus of the cat

Extracellular spikes were recorded from cell bodies of sympathetic preganglionic neurones in spinal segments T1-T3 of the cat. Each neurone was identified by its antidromic response to electrical stimulation of the sympathetic chain and was found in histological sections to lie within the intermediolateral nucleus. Physiological properties studied in detail included basal activity, spike configuration, and latency of antidromic activation. Also studied, in tests with paired stimuli, were the threshold interstimulus interval evoking two responses, as well as changes in amplitude and latency of the second spike which occurred at intervals near this threshold. Approximately 60% of the units studied were spontaneously active, the rest were silent. Spontaneous activity was characterized by a slow (mean = 3.1 +/- 2.6 (SD) spikes/s), irregular pattern of discharge. With approximately one-third of the cases there was a periodic pattern of discharge in phase with oscillations in blood pressure. This correlation of phasic activity suggests that many of the units studied were involved specifically in cardiovascular function. Silent and spontaneously active units could not be differentiated on the basis of latency of antidromic activation or threshold interstimulus interval; mean latency for the two groups was 7.2 +/- 4.9 ms, mean threshold interval was 6.4 +/- 4.7 ms. Thus, with the exception of basal activity, the physiological properties studied failed to indicate more than a single population of neurones. These results therefore suggest that the sympathetic preganglionic neurones in the intermediolateral nucleus subserving varied autonomic functions share overlapping physiological properties, and that functional differentiation of these neurones may be based on differences in synaptic inputs.     

Comparative analysis of background activity of ventrolateral thalamic neurons in patients with parkinsonism and torsion muscle dystonia

In the course of neurosurgical interventions in 40 patients with parkinsonism and torsion muscle dystonia, the background activity (BA) was recorded from 124 neurons of the ventrolateral nucleus (VL) of the thalamus with the aid of microelectrodes during demarcation of boundaries between nuclear structures, and identification of zones within a nucleus. The following characteristic features of the BA in patients with parkinsonism were found: a relatively large proportion (71%) of cells with a burst pattern of activity; a great diversity of burst duration in the activity (short or prolonged bursts); a large proportion (67%) of cells with cyclic changes in the BA frequency; diverse patterns of cyclic modulation, where periods varied from fractions of a second (0.2–0.8 sec) to seconds (2–10 sec) or to tens of seconds (20–40 sec); cyclic successions of spike bursts with the rhythm typical of the peripheral tremor (3–7/sec) in a substantial proportion (40%) of the units.The background spike trains recorded in patients with torsion muscle dystonia consisted of separated spikes in the majority (69%) of units. Only short high-frequency discharges were found in the burst activity in this group; a cyclic BA pattern occurred much less frequently (in 23% of neurons); burst discharges at a 3–4/sec frequency were found only in 4% of the examined cells.The possible nature of motor disorders in patients with parkinsonism and torsion muscle dystonia and the mechanisms of the curing effects of cryodestruction of theVL of the thalamus in the treatment of the disease are discussed.Neirofiziologiya/Neurophysiology, Vol. 25, No. 4, pp. 246–253, July–August, 1993.     

Bursting as an Effective Relay Mode in a Minimal Thalamic Model

In recent years, accumulating evidence indicates that thalamic bursts are present during wakefulness and participate in information transmission as an effective relay mode with distinctive properties from the tonic activity. Thalamic bursts originate from activation of the low threshold calcium cannels via a local feedback inhibition, exerted by the thalamic reticular neurons upon the relay neurons. This article, examines if this simple mechanism is sufficient to explain the distinctive properties of thalamic bursting as an effective relay mode. A minimal model of thalamic circuit composed of a retinal spike train, a relay neuron and a reticular neuron is simulated to generate the tonic and burst firing modes. The integrate-and-fire-or-burst model is used to simulate the neurons. After discriminating the burst events with criteria based on inter-spike-intervals, statistical indices show that the bursts of the minimal model are stereotypic events. The relation between the rate of bursts and the parameters of the input spike train demonstrates marked nonlinearities. Burst response is shown to be selective to spike-silence-spike sequences in the input spike train. Moreover, burst events represent the input more reliably than the tonic spike in a considerable range of the parameters of the model. In conclusion, many of the distinctive properties of thalamic bursts such as stereotypy, nonlinear dependence on the sensory stimulus, feature selectivity and reliability are reproducible in the minimal model. Furthermore, the minimal model predicts that while the bursts are more frequent in the spike train of the off-center X relay neurons (corresponding to off-center X retinal ganglion cells), they are more reliable when generated by the on-center ones (corresponding to on-center X ganglion cells).     

Spike firing pattern of output neurons of the Limulus circadian clock

The lateral eyes of the horseshoe crab (Limulus polyphemus) show a daily rhythm in visual sensitivity that is mediated by efferent nerve signals from a circadian clock in the crab's brain. How these signals communicate circadian messages is not known for this or other animals. Here the authors describe in quantitative detail the spike firing pattern of clock output neurons in living horseshoe crabs and discuss its possible significance to clock organization and function. Efferent fiber spike trains were recorded extracellularly for several hours to days, and in some cases, the electroretinogram was simultaneously acquired to monitor eye sensitivity. Statistical features of single- and multifiber recordings were characterized via interval distribution, serial correlation, and power spectral analysis. The authors report that efferent feedback to the eyes has several scales of temporal structure, consisting of multicellular bursts of spikes that group into clusters and packets of clusters that repeat throughout the night and disappear during the day. Except near dusk and dawn, the bursts occur every 1 to 2 sec in clusters of 10 to 30 bursts separated by a minute or two of silence. Within a burst, each output neuron typically fires a single spike with a preferred order, and intervals between bursts and clusters are positively correlated in length. The authors also report that efferent activity is strongly modulated by light at night and that just a brief flash has lasting impact on clock output. The multilayered firing pattern is likely important for driving circadian rhythms in the eye and other target organs.     

On the complex dynamics of intracellular ganglion cell light responses in the cat retina

We recorded intracellular responses from cat retinal ganglion cells to sinusoidal flickering lights, and compared the response dynamics with a theoretical model based on coupled nonlinear oscillators. Flicker responses for several different spot sizes were separated in a smooth generator (G) potential and corresponding spike trains. We have previously shown that the G-potential reveals complex, stimulus-dependent, oscillatory behavior in response to sinusoidally flickering lights. Such behavior could be simulated by a modified van der Pol oscillator. In this paper, we extend the model to account for spike generation as well, by including extended Hodgkin-Huxley equations describing local membrane properties. We quantified spike responses by several parameters describing the mean and standard deviation of spike burst duration, timing (phase shift) of bursts, and the number of spikes in a burst. The dependence of these response parameters on stimulus frequency and spot size could be reproduced in great detail by coupling the van der Pol oscillator and Hodgkin-Huxley equations. The model mimics many experimentally observed response patterns, including non-phase-locked irregular oscillations. Our findings suggest that the information in the ganglion cell spike train reflects both intraretinal processing, simulated by the van der Pol oscillator, and local membrane properties described by Hodgkin-Huxley equations. The interplay between these complex processes can be simulated by changing the coupling coefficients between the two oscillators. Our simulations therefore show that irregularities in spike trains, which normally are considered to be noise, may be interpreted as complex oscillations that might carry information.To the memory of Prof. Otto-Joachim Grusser     

Proctolin potentiates synaptic transmission in the central nervous system of an insect

1. Bursts of spike activity in the ventral nerve cord of the cockroach were elicited by mechanically stimulating the cercal organs. 2. In the presence of micromolar proctolin, the peak frequency and the duration of a burst were slowly but significantly increased. 3. In contrast, carbachol produced an immediate enhancement of spontaneous activity, but a potentiation of bursts was not seen. 4. It is proposed that proctolin functions as a neuromodulator in the terminal abdominal ganglion of the cockroach.     

Unit activity of rabbit medial septum in early ontogenesis]

In experiments on 7-20 and 75-day-old rabbits, the activity of units of the septal nuclei, the nucleus of the diagonal band of Broca (NBD), nucleus medialis (NSM) and the EEG of dorsal hippocamp (the CA2-CA3 fields) have been recorded. It was shown that the specific discharge pattern of septal neurons (the bursts) appears on 8-11th days under action of eserine. The distinct bimodal pattern of the interval histograms of the septal units appeared from the 14th day. The burst discharge pattern of NBD and NSM neurones reached a definitive level by the 20th day. The parallel evolution of discharge pattern of the septal units and the EEG of the hippocamp is observed in ontogenesis, the formation of hippocampal theta activity correlating with enhancement of the average frequency of the septal (NBD, NSM) neuronal activity, with shortening to the interval between the discharges within the bursts and with enhancement of the regularity of the bursts.     

Probing real sensory worlds of receivers with unsupervised clustering

The task of an organism to extract information about the external environment from sensory signals is based entirely on the analysis of ongoing afferent spike activity provided by the sense organs. We investigate the processing of auditory stimuli by an acoustic interneuron of insects. In contrast to most previous work we do this by using stimuli and neurophysiological recordings directly in the nocturnal tropical rainforest, where the insect communicates. Different from typical recordings in sound proof laboratories, strong environmental noise from multiple sound sources interferes with the perception of acoustic signals in these realistic scenarios. We apply a recently developed unsupervised machine learning algorithm based on probabilistic inference to find frequently occurring firing patterns in the response of the acoustic interneuron. We can thus ask how much information the central nervous system of the receiver can extract from bursts without ever being told which type and which variants of bursts are characteristic for particular stimuli. Our results show that the reliability of burst coding in the time domain is so high that identical stimuli lead to extremely similar spike pattern responses, even for different preparations on different dates, and even if one of the preparations is recorded outdoors and the other one in the sound proof lab. Simultaneous recordings in two preparations exposed to the same acoustic environment reveal that characteristics of burst patterns are largely preserved among individuals of the same species. Our study shows that burst coding can provide a reliable mechanism for acoustic insects to classify and discriminate signals under very noisy real-world conditions. This gives new insights into the neural mechanisms potentially used by bushcrickets to discriminate conspecific songs from sounds of predators in similar carrier frequency bands.     

Inhibitory effects of neuropeptide Y (NPY) on CRF and stress-induced cecal motor response in rats

The effects of NPY on CRF and stress-stimulated cecal motility were investigated by electromyography in rats. Intracerebroventricular (ICV) injection of NPY at 300 ng/kg significantly reduced the frequency of spike burst during the first 15 minutes after its administration while no effect was observed at a lower dose (150 ng/kg). Exposure to mental stress (MS) increased significantly (p less than 0.01) during 45 minutes, the frequency of cecal spike bursts. NPY (300 ng/kg) injected ICV, 30 minutes prior to MS periods abolished the excitatory effect induced by stress. The frequency of cecal spike bursts was also increased during the first 15-minutes following ICV injection of CRF (300 ng/kg). Prior (5 min) ICV administration of NPY (150 ng/kg) abolished the stimulatory effect of CRF on cecal motility. It is concluded that central administration of NPY suppresses the stress-induced cecal motor response probably by inhibiting the pathways involved in CRF mediation of these effects.     

Types of spontaneous discharges of muscle receptors

Characteristics of discharges of 462 muslce spindle receptors located in the deefferented triceps surae muscle with a divided tendon were analyzed in anesthetized cats. Of the total number, 205 units had spontaneous activity which, depending on its stability, could be divided into three types. A long continuous spike train was generated by 87% of units. Distributions of interspike intervals were unimodal and symmetrical. Spontaneous activity of this type was more regular in secondary than in primary endings. Action potentials in 8% of units were grouped in volleys and interval distributions were bimodal. Spontaneous activity of the remaining 5% of units was characterized by sporadically appearing spikes with long intervals between them. The first two types of spontaneous activity cannot be placed in the category of stochastic processes. Threshold discharges during static stretching of the muscle sufficient to cause the appearance of a long spike train were studied in 231 of 257 initially "silent" units. By the same criteria these discharges were divided into corresponding types. Comparison of the characteristics of spontaneous activity and evoked responses suggests that they share the same mechanism of origin. It is concluded that the spontaneous discharge can be regarded as a static response of the receptors due not to an externally applied stretching load, but to the action of internal factors, depending on interaction between extrafusal and intrafusal muscle fibers.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 13, No. 3, pp. 315–321, May–June, 1981.     

Bursts and isolated spikes code for opposite movement directions in midbrain electrosensory neurons

Directional selectivity, in which neurons respond strongly to an object moving in a given direction but weakly or not at all to the same object moving in the opposite direction, is a crucial computation that is thought to provide a neural correlate of motion perception. However, directional selectivity has been traditionally quantified by using the full spike train, which does not take into account particular action potential patterns. We investigated how different action potential patterns, namely bursts (i.e. packets of action potentials followed by quiescence) and isolated spikes, contribute to movement direction coding in a mathematical model of midbrain electrosensory neurons. We found that bursts and isolated spikes could be selectively elicited when the same object moved in opposite directions. In particular, it was possible to find parameter values for which our model neuron did not display directional selectivity when the full spike train was considered but displayed strong directional selectivity when bursts or isolated spikes were instead considered. Further analysis of our model revealed that an intrinsic burst mechanism based on subthreshold T-type calcium channels was not required to observe parameter regimes for which bursts and isolated spikes code for opposite movement directions. However, this burst mechanism enhanced the range of parameter values for which such regimes were observed. Experimental recordings from midbrain neurons confirmed our modeling prediction that bursts and isolated spikes can indeed code for opposite movement directions. Finally, we quantified the performance of a plausible neural circuit and found that it could respond more or less selectively to isolated spikes for a wide range of parameter values when compared with an interspike interval threshold. Our results thus show for the first time that different action potential patterns can differentially encode movement and that traditional measures of directional selectivity need to be revised in such cases.     

Activity of neurons of the motor zone of the cortex during elaboration of a local instrumental defensive reflex in the rabbit

During instrumental defensive reaction of wrist extension in response to a sound (conditioned) stimulus, two types of neuronal responses in the rabbit motor cortex were discovered. The first type was recorded in cells with activity not connected with electromyographic activity of wrist extensors. The reaction consisted in the appearance of inhibitory response at the place of the cancelled electrocutaneous stimulation at animal's performance of conditioned reaction to sound. The second type of responses was shown for a neurone with the activity significantly related to electromyographic activity. In this case the conditioned motor response was accompanied by enhancement of the cellular activation reaction to sound and the increase of spike activity in interstimuli intervals.