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PubMedDate not supplied

[Model of nerve net learning based on changes in the efficiency of excitatory and inhibitory synapses].

Based on recent data on learning neurophysiology, a dynamic model of a nervous network was created, consisting in systems of locally connected excitatory and inhibitory elements and general excitatory and inhibitory systems. Interneuronal interactions were realized by means of imitation of impulse transmission of information, spatial-temporal summation of excitatory and inhibitory influences, the effect of "disinhibition" by the mechanism, imitating the depression of inhibitory elements during overexcitation and presynaptic inhibition of inhibitory systems. When learning the model, the Hebb's principle was applied, i. e. and irreversible increase of synaptic transmission after coincidence of activation of pre- and postsynaptic neurones. The processes, imitating the elaboration, extinction and recovery of conditioned reflex were studied. Some initially unforeseen effects were revealed. The universal properties of the model are being discussed.

Animals↗
PubMedDate not supplied

[Excitatory interactions in the nerve nets switching on the cells of the auditory cortex and the medial geniculate body].

Crosscorrelation method was used for revealing effective monosynaptic excitatory interactions in neural networks containing simultaneously recorded neurons from different loci of auditory cortex (A1) and medial geniculate body (MGB). It was shown that (a) there were effective reciprocal excitatory connections between neurons in different loci of A1 and MGB; (b) connections between neurons in tonotopic loci of A1 and MGB and in adjacent cortical loci were the most effective; (c) connections were "divergent", i.e., one neuron in A1 (MGB) excited neurons in different loci of A1 and MGB simultaneously; (d) connections were "convergent", i. e., one neuron in A1 (MGB) was excited by neurons from different loci of A1 and MGB simultaneously. We suggest that this principles of organization of excitatory connections in thalamo-cortical networks promoted the induction of long-term changes (LTP and LTD) in excitatory synaptic efficacy and that this mechanism underlie the observed changes of receptive fields of A1 and MGB neurons induced by intracortical microstimulation.

Action Potentials↗
PubMed1986

[Mechanisms of the formation of long-periodicity oscillations in activity in nerve nets. Nets with pre- and postsynaptic inhibition].

The role of presynaptic and postsynaptic processes in formation of the long-term (hundreds of milliseconds) activity of neuronal networks was analyzed by the mathematical simulation model. The long-term activity of networks with presynaptic inhibition was discontinued due to the depolarization of the neuronal terminals that achieved its critical level and to significant suppression of the effectiveness of synaptic interaction. The long-term activity of networks with postsynaptic inhibition was discontinued because of the activation of inhibitory neurons exerting strong hyperpolarizing effects on other neurons of the networks. Synchronization of neuronal discharges was important in achievement of the critical level by terminal depolarization or inhibitory postsynaptic processes that interrupted the network activity. Properties of neuronal networks with presynaptic and postsynaptic inhibition were compared with those of uniform neuronal networks (with a positive feedback between neurons only). It is concluded that introduction of the additional negative feedback circuits in a form of presynaptic or postsynaptic inhibition contributes to improvement of reliability and accuracy of the mechanism which terminates the network activity.

Computers↗