Impulse Activity Of Neurons Research Articles

Markov process of maintained impulse activity in central single neurons.

To clarify the stochast properties of the maintained impulse activity of the central nervous system, we proposed a measure of statistical dependency on the basis of Shannon's entropy. This measure could provide the Markov properties of the neural impulse sequences, representing the necessary and sufficient condition for the statistical dependence. The order of Markov process of the sequence is determined by the conditional entropy which is derived from the joint entropy. Here the joint entropy in the case of Gaussian process is directly related with the covariance matrix which is substituted for the matrix of the serial correlation coefficients. Therefore the condition to determine the order of Markov process is obtained by the equation of the matrices of the serial correlation coefficients. The order of Markov process of the neural impulse sequences recorded from the mesencephalic reticular formation (MRF), red nucleus (RN), and lateral geniculate nucleus (LGN) neurons has been estimated. The maintained impulse activity of the MRF and RN neurons had from the 2-nd to 4-th order Markov property, while that of the LGN had no Markov property, in the consecutive impulse sequences.

Change in reactions of visual cortex neurons to light flash upon hypothalamic and reticular stimulation

The effect of electrical stimulation of the hypothalamic positive reinforcement zone (PRZ), the neutral hypothalamic zone (NZ), and the reticular formation (RF), of the midbrain on the impulse activity of single neurons of the visual cortex evoked by light flashes was studied in unanesthetized and uncurarized white rats. Poststimulus histograms of the neurons's responses were compared. Under the influence of stimulation the evoked activity of the neurons which responded to light changed in a majority of them (from 63% for the NZ to 82% for the RF). Qualitative differences were found in the effects of PRZ and RF stimulation. The effects of PRZ stimulation consisted in the invariability or in a decrease in the frequency of the neuron's discharge comprising the short-latent response, and an increase in the frequency of the discharges in the long-latent response ("positive-motivation" type). The effects of RF stimulation were manifested in intensification of the neuronal discharges in the short-latent and a decrease in the discharges in the long-latent response ("reticular" type). The responses of a considerable number of the neurons changed to the "combined" type. The data obtained indicates the different natures and mechanisms of the ascending activating effects caused by stimulation of the PRZ and the RF and which brings about positive nonspecific reinforcements. These effects, which are manifested differently in different periods of the neuron's working cycle cannot be explained by "energizing" or "tonus" concepts; their explanation must be sought for in informational (systemic) concepts.

Neuron activity in areas of the hypothalamic nuclei in rabbits after intraventricular administration of vasopressin and oxytocin

Intraventricularly applied vasopressin ncreased, and oxytocin decreased, the impulse activity of neurones in the paraventricular and supraoptic nuclei. We found a shorter reaction time for the paraventricular nucleus in comparison with the supraoptic nucleus.

Activity of caudal mesenteric ganglion in relation to its impulsation (age aspect)

It has been shown in acute experiments on cats and kittens that the pre- and postganglionic nerves of the caudal mesenteric sympathetic ganglion (CMSG) are bioelectrically active from the first day of the animal's life. When the impulsation which comes to the ganglion along the afferent and preganglionic fibers is removed, the impulse activity of the post-ganglionic neurons disappears completely. In newborn kittens the level of activity of the postganglionic fibers is determined to a greater degree by the afferent impulsation of the hypogastric nerves than in adult cats. The effect of the preganglionic impulsation, especially that coming through the intramesenteric nerves, predominates in adult animals. The efferent impulsation of the hypogastric nerves in cats not older than five days disappeared after sectioning of two to three preganglionic branches of the CMSG; in six to nine and 14 to 15-day-old cats, after sectioning of four and in month old cats after sectioning of five; and in two to three month old cats after sectioning of six branches. In adult cats after the first sectioning the postganglionic impulsation frequently intensified, and after sectioning of seven branches the activity completely disappeared. Automatic activity of the ganglia was not observed, postganglionic impulsation developed and changed under the influence of the impulses coming to the ganglion.

Minor tranquillizers, stress and central catecholamine neurons

The effects of chlordiazepoxide, diazepam and nitrazepam on central DA and NA neurons of non-stressed and stressed rats were studied using histochemical and biochemical analysis of DA and NA. Estimations of DA and NA turnover in various regions of the brain were obtained by studying the decrease in stored DA and NA following treatment with a tyrosine hydroxylase inhibitor (H44/68) or a DA-β-hydroxylase inhibitor (FLA63). Stress was induced by immobilization. (1) Stress increased NA turnover in all parts of the brain and the spinal cord. By biochemical methods it was shown that DA turnover in the telencephalon was significantly reduced. (2) By histochemical methods it was shown that chlordiazepoxide and diazepam decreased NA turnover in the cortex cerebri and cortex cerebelli and the hippocampal formation but did not do so to any significant extent in the hypothalamus or the lower brain stem. These results show that the benzodiazepine derivatives decrease the impulse activity in the NA neurons of the locus coeruleus which innervate all cortices of the brain. (3) Chlordiazepoxide and diazepam caused a small but significant decrease in DA turnover in ascending DA neurons to the neostriatum and the limbic forebrain indicating reduced impulse flow in these neurons. (4) Chlordiazepoxide, diazepam and nitrazepam caused a blockade of the stress-induced activation of NA neurons by decreasing nervous activity in these neurons. (5) Chlordiazepoxide and diazepam potentiated the stress-induced decrease in nervous activity in ascending DA neurons. Stress combined with these drugs therefore decreased DA turnover in the telencephalon in comparison with normal controls. In view of the role which the central NA and DA neurons probably play in behavioral and EEG arousal it seems that the decrease in nervous activity in DA and NA neurons produced by chlordiazepoxide and diazepam may be responsible for part of the pharmacological effects of these tranquillizers such as sedation and EEG slowing.

Electric responses of the cerebral cortex to central excitation and inhibition

An attempt was made to evaluate critically the extent to which the background electrocorticogram, neuronal impulse activity, and evoked potentials reflect the state of cortical excitation and inhibition. It was shown that during electrocorticogram desynchronization, firing neurons predominated in the surface (mainly afferent) layers, while inhibited neurons were in the majority in the lower layers of the cortex. Consequently, desynchronization does not reflect diffuse excitation of the cortex and cannot be taken as an index of central excitation. Slow electrocortical waves cannot be used as indicators of an inhibitory state, even though they may be associated with processes leading to the development of inhibition. Under the effects of different stimuli, the number of neurons participating in impulse condition, and the number of neurons temporarily inhibiting impulse activity in the projection cortical area were stable (ratio 2:1). It was found that the correlation between impulse discharges of neuronal pairs increases during both central excitation and central inhibition. Nonetheless, differences between cortical excitation and inhibition were seen in the reorganization of neuronal columns. The use of evoked potentials to determine cortical excitation or inhibition is complicated by the fact that the amplitude of evoked-potential components reflects the divergent influences of many factors. It was shown that conditional excitation diminished the evoked potential to a light stimulus in the projection cortical area, but caused it to increase in the region of the motor analyzer. The elaboration of a conditional inhibition (extinction) is accompanied by the growth of an evoked potential to a stimulus in the primary cortical area, and by its repression in the region of the motor analyzer. In this case, a large delayed negative wave appears in the evoked potential.

Stochastic properties of spontaneous impulse activity in central single neurons.

Stochastic dependence of the consecutive interspike intervals of the spontaneous discharges of the central single neurons has been studied in cats. Out of 35 neurons examined with the stationarity test, 16 passed it: 3 from the ventrobasal complex where the modality was hair (VB), 6 from the lateral geniculate nucleus (LGN), 4 from the mesencephalic reticular formation (MRF), and 3 from the red nucleus (RN). The interspike interval histogram in the VB and the LGN nuerons resembled the exponential and the bimodal distribution, while that in the MRF and the RN neurons did the gamma distribution. The quantitative measures of correlation between interspike intervals were furnished by the serial correlation coefficient, the variance function and the joint interval histogram. They showed that there were no correlation in most of the VB and the LGN neurons, while there existed correlation in most of the MRF and the RN nuerons. Approximately similar results were obtained by the X2 test for Markov process. A new quantitative measure which reflects Markov properties of the consecutive impulse sequences has been developed. It estimates the statistical dependency, d(τ), on the basis of Shannon's entropy. It has been confirmed theoretically that this measure is applicable in practice. The value of d(τ) of adjacent interspike intervals obtained from the VB and the LGN neurons was approximately equal to that of the shuffled ones, while that from the MRF and the RN neurons was larger than that of the shuffled ones. This is to be regarded as the evidence of the fact that the spontaneous impulse activity of the VB and the LGN neurons has no Markov property, while that of the MRF and the RN neurons has at least first order Markov property. The differentiation in two groups of the neurons is suggested to correlate with other functional characteristics of these neuron populations. However, the number of neurons sampled would have to be increased several-fold before the statistical differences in patterns of discharge could be made the basis for widely applicable generalizations about function.

Use of the principles of computer statistical analysis for investigating the background impulse activity of neurons

A program for complex statistical analysis of the background impulse activity of neurons on a computer is proposed. The program includes: determination of the portion of the recording having a stable statistical structure; calculation of histograms of the probability density function of the interspike intervals (ISI) and statistical indexes related with them; correlation-spectral analysis of the ISI sequence; correlation-spectral analysis of the instants of appearance of impulses (from the frequency graph and graph of the function of recovery of impulse activity); and determination of the type and degree of relation of the lengths of adjacent ISI's and entropy analysis of this connection. A method is described for determining the portion of burst and group activity of the investigated neuron in the recording. The effectiveness of using the proposed program was checked by analyzing the background activity of pyramidal cells of the cat cortex. An analysis of neurons equal in frequency of background activity and rate of conduction of impulses in axons showed that the differences in the internal statistical structure of their impulses are very substantial.

Dynamics of the single unit reactions in the visual cortex of the unanesthetized rabbit

The impulse activity of the visual neurons of an unanaesthetized rabbit was-recorded with the help of tungsten microelecirodes. According to the character of the background activity. the neurons are divided in 4 groups. The responses to a flash are determined by the correlation of the phases of excitation and inhibition; on this basis the neurons are divided into excitatory, excitatory-inhibitory, inhibitory, inhibitory-excitatory and non-responsive groups. The action of a sound (a click, the noise of the motor of a “recordina”) is characterized mainly by inhibition of both the background and the light-evoked activities. During rhythmic repetitions of the flashes the responses of the visual neurons manifest a marked stability. The following forms of dynamic changes taking place during repetitions of the light flashes, as well as of the complex of a click - a flash were established: stabilization of the responses (20.7 per cent): partial extinction (about 17 per cent); intensification (5 per cent): conditioning to time (10 per cent): sound and light association (8 per cent). The repeated presentations of a sound stimulus result in a complete extinction of the neuronal responses. The data obtained are explained as a convergence of specific and nonspecific influences on the visual neurons. It is supposed that conditioning on the neuronal level is due to a particular type of convergence, namely, “plastic convergence”. The data obtained refer to the sensory interaction studied at psychophysiological level.

Effect of hypercapnia and hypocapnia on impulse activity of inspiratory and expiratory neurons of the reticular formation of the medulla

Effect of hypercapnia and hypocapnia on impulse activity of inspiratory and expiratory neurons of the reticular formation of the medulla

Response in units of inferior colliculus in cats to unilateral change of intensity of a binaural stimulus

1. The impulse activity of neurons of the inferior colliculus of cats was investigated by varying the intensity of one of a binaural pair of stimuli. Several types of neuronal responses were discovered, characterized by an increase or decrease of activity, as a rule at strictly demarcated intensities of the variable stimulus. The changes in intensity of most neurons are reciprocal in character. 2. Comparison with data in the literature concerning changes in neuronal activity of the superior olive suggests that the main tendency of transformation in activity between these portions of the auditory system during variation in intensity of one of a binaural pair of stimuli is a change from gradual (linear) changes in discharge throughout the range of variation of intensity (superior olive) to nonlinear changes in discharge, strictly limited to definite values of the varied intensity (inferior colliculus). These intensities are specific for a particular neuron, but differ from one neuron to another, thus covering the whole range of intensities used.

Spontaneous spike potentials of single neurons in situ in ganglia of the leech

In experiments on leeches it was found that potentials of single neurons can be recorded from the neural ganglion in situ. The spike discharges of most single neurons in these conditions do not possess extreme properties: neither strict orderliness, especially rhythmicity of their activity, nor absolute randomness of the Poisson type. The discharge pattern is distinguished by variability and, at the same time, by some degree of ill defined orderliness, i.e., positive correlation. Consequently, the dynamic connections between neurons, even in primitive nerve structures, are complex. The factors determining the slight degree of orderliness (cyclic character) of impulse activity of neurons in these conditions are still unknown.

Statistical machine analysis of the impulse activity of individual neurons

Statistical machine analysis of the impulse activity of individual neurons

Central Organization of Nervous Processes and the Basic Impulse Activity of Neurons

1) The neuron organization of nervous proccesses in the higher divisions of the brain are characterized by rising arrhythmia and asynchrony of "spontaneous" impulses with a relative reduction in the number of neurons yielding spontaneous discharges.

The relationship between the background impulse activity of cortical neurons and the electrocorticogram phases

The relationship between the background impulse activity of cortical neurons and the electrocorticogram phases