Background Impulse Activity Research Articles

Prolonged excitation of individual neocortical neurons, structure of background impulse activity

The background impulse activity of individual neurons was recorded extracellularly in the cerebral cortex of the cat during the prolonged microionophoretic delivery to these neurons of L-glutamate. Glutamate ionophoresis ensured the transition of the neuron to an elevated, but stable level of activation. An autocorrelation analysis of the trains of impulses showed that in spite of the multiple rise in the average discharge frequency, the type of background impulse activity and the periods of increased and reduced probability of discharges for the most part remained constant. The obtained data indicate that an individual cell is unable to influence substantially the interneurons connected with it, while the type of background activity of a neuron is determined primarily by the level of activation of the cellular ensemble incorporating this neuron.

Change in the activity of cortical neurons under the influence of biogenic amines.

Under the conditions of extracellular recording of action potentials, the influence of proposed neuromediators on the structure of background impulse activity of neurons of various regions of the cerebral cortex was studied. Computer analysis of the statistical parameters of impulse flows revealed the presence of a fundamental difference between the effects of neuromediators of cortical and subcortical origin. It was demonstrated that prolonged application of serotonin and noradrenalin evokes a change in structure of cortical neuron impulse activity more complex than the simple inhibition and excitation characteristic of acetylcholine or GABA. Different types were found of the reaction of neurons to the same monoaminergic stimulus, types whose characteristic feature is the dependence of the end result of the influence on the initial level of excitation in the neuron examined. The fundamental difference between the effects of preparations studied in the visual and sensorimotor regions of the cortex was not discovered. The data obtained are considered from the point of view of the modulating role of the biogenic amines in the regulation of the level of excitation of cerebral cortical neurons.

Cross-correlation analysis of the background impulse activity of cells located at various distances in the visual cortex of the alert rabbit.

1. In a microarea of the visual cortex with tangential dimensions of not more than 300 μ dependent relations between neurons are most often (80%) exhibited when recording cells with one electrode. With an increase of the distance between neurons the number of independently working pairs decreases. 2. The greatest diversity of the forms of cross-correlation functions is found for adjacent neurons recorded by one electrode. Only wide symmetric cross-correlation functions or one-bin overshoots are characteristic for the activity of cells recorded by two electrodes regardless of the distance between them. 3. Discharges of adjacent neurons with a large amplitude of the spikes lead discharges of cells with a small amplitude. For distant cells dependent relations are most often observed between neurons with small spikes. 4. For adjacent cells the modes of significant extremes are located mainly in the range of time delays up to 10.5 msec. With an increase of distance between neurons extremes shifted by the amount of delays greater than 10.5 msec occur in the cross-correlation functions with noticeable probability.

Convergent properties of three types of visual-cortex neurons recorded with different action-potential amplitudes

1. The responses of neurons recorded with a large (N1), medium (N2), and small (N3) action potential (AP) amplitude to light, sound, and electrocutaneous stimulation were investigated in the region of field 18 in the visual cortex of cats. Regardless of the modality of the presented stimulus, responses of the inhibitory type were more frequently observed in group N1 and N2 neurons than in group N3 neurons. 2. A significant number (46%) of tri- and bimodal cells was found; such cells were encountered more frequently among group N1 neurons than group N2 and N3 neurons. 3. Comparison of the character of the responses of each of the cells to stimuli of various modalities made it possible to postulate that the inhibitory responses of group N1 and N2 neurons are provided for by inhibitory interneurons that receive converging signals of all three investigated modalities. Apparently, only nonvisual stimuli converge on the excitatory neurons located at the input of N1 and N2 cells. 4. It is believed that the unitypic excitatory responses of group N3 neurons are provided for by the convergence on them of independent inputs from stimuli of various modalities. 5. A correlation was found between the “responsive” properties of cells and the structure of their background impulse activity. 6. The conclusion was made concerning the functional heterogeneity of neurons recorded with different AP amplitudes.

Computer Analysis Dynamics of Background Impulse Activity of Neurons in Situ and in Vitro

Statistical characteristics of background impulse activity of pyramide neurons of hippocampus in situ and in vitro were compared. The results of statistical analysis have shown a good coincidence of numerical characteristics of distribution of inter-impulse intervals: mathematical expectancies, standard deviations, coefficients of asymmetry and excess in impulse flows of the compared series. This coincidence can serve as one of proofs of preservation of normal functional properties and “organospecificity” by the neurons is tissue culture.On the other hand, some differences were found in the structure of the compared flows, which the authors attribute to essential differences between the neuronal networks in the objects studied.

Afferent signal transformation at subcortical levels of the visual system

A comparison was made of the characteristics of the background and light-induced impulse activity of 350 neurons of the retina and laterial geniculate body (LGB) of an immobilized cat. In the LGB, in contrast to the ganglion cells of the retina, there are relatively more neurons with high-light sensitivity, low latency of response, short-initial discharge, and low summation time, as well as rapid recovery of reactivity. It was found that these changes are characteristic of cells connected with the peripheral region of the retina. In the central channel and the system of long-latency cells, according to a number of parameters, no such transformations are found, while other characteristics change in the opposite direction. In the central channel at the postgenicular level, the frequency of the background and induced impulsation decreases, while in the peripheral channel it increases considerably. The results obtained indicate differences in the organization of the synaptic inputs of LGB neurons of different groups. The intensification and time compression of the sensory transmission in the peripheral channel are explained by the reticular properties of the structures formed by the branching and overlapping fibers coming from the retina, as well as by the great effectiveness of the successive inhibition in the LGB which blocks the late group of initial discharges. These transformations of the afferentation can provide reliability and rapidity of the detection of weak, slowly increasing, and moving light signals.

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.

Influence of afferent impulses from the nerves of the anterior limbs on the insertion neurons of the lumbar section of the spinal cord

In anesthetized cats in conditions of muscular relaxation we have studied the participation of the interneurons of the lumbar section of the spinal cord in the interaction of the FRA systems of the fore and hind limbs. Using microelectrodes we have made extra- and intracellular recordings of the potentials. It has been shown that from the flexor afferents of the fore limbs both facilitating and inhibitory influences are transmitted. The former are expressed in increased frequency of the background impulse activity of the neurons, in the appearance of evoked responses of the "silent" cells and intensification of the test responses for short time intervals with paired heteronymous stimulation. The inhibitory influences prevail over the facilitating and are manifest in depression of the background activity and evoked segmental responses of the neurons. The maximum inhibition of the segmental responses was noted for intervals of 40–140 msec. The duration of inhibition varied from 100–500 msec and more. Depending on the intensity and duration of the inhibitory influences two groups of interneurons have been isolated. The role of the pre- and postsynaptic mechanisms in the transmission of inhibitory influences from the afferents of the fore limbs on the afferents of the hind limbs is discussed.

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

Character of the efferent impulses in the postganglionic fibers of the splanchnic nerve during vasoconstrictor and vasodilator reactions in the abdominal organs

Recording of efferent impulsation in the central ends of the mesenteric, renal and splenic nerves has made it possible to establish the presence of a background impulse activity in all three nerves. Following stimulation of the peripheral end of the greater splanchnic nerve the impulse activity in these nerves changed in accordance with the frequency and strength of the stimulation. It may be considered that vasoconstrictor and vasodilator effects are dependent upon the stimulation intensity of preganglionic fibers of the splanchnic nerve, and concomitant quantitative changes in the terminal impulsation of the postganglionic vasomotor fibers.