The reflection of the plastic properties of the simplest neuronal junctions in the statistical characteristics of the impulse activity of their elements. Polysynaptically linked neurons

Conclusions

• 1. The regularities of change in the normalized histogram of the correlation of impulse trains of disynaptically linked neurons, in the presence of changes in efficiency of interneuronal, monosynaptic links, in the excitability of neurons, and in the summated effect upon them of independent, irregular, afferent, synaptic inputs, were studied, using a mathematical model of neuronal interaction.

• 2. The amplitude of the basic maximum (minimum) of the normalized histogram of disynaptically linked neurons (meaning also the degree of dependence of their impulse trains) increases both with increase in the amplitude of the postsynaptic potentials which allow for a functional link between these neurons, and with decrease in the frequency of discharges of any of them (but not of the interneuron) which is conditional upon a decrease in the sweep of the irregular, exogenous oscillations of its membrane potenital or an increase in the threshold of generation of the impulse.

• 3. In the case of an excitatory, disynaptic link between the neurons, the increase in the degree of dependence of their impulse trains has a limit, determined by the greatest of the mean frequencies of the discharges of the pre- and postsynaptic neurons.

• 4. It is impossible only by the character of the modification of the cross-over-correlational histogram of the impulse trains of polysynaptically linked neurons to establish the true physiological cause of this modification. It is necessary also to take into account the character of the mean frequency of the discharges of the neurons studied.

• 5. The increase in the amplitude of the basic maximum (if the link is excitatory), or of the basic minimum (if the link is inhibitory), of the normalized cross-over-correlational histogram of their impulse trains, which accompanies the increase in the mean frequency of the discharges (the decrease in mean interspike intervals) of both neurons, is an unambiguous indicator of an increase in the efficiency of the disynaptic link between neurons (as a result of modification of synapses or change in the functional state of the interneuron).