Analysis of spike activity of two neurons monosynaptically excited by a third, using cross-correlation histograms and Cos' method. Possibility of detecting plasticity of neurons and synapses.

Exogenous stationary random single spike activity of two neurons (N1 and N2), monosynaptically excited by a third (N3), was reproduced by a mathematical model. The degree of dependence of spike trains of N1 and N2 was assessed by the value of P12, determined by cross-correlation histogram, and Cox' coefficient B12. The dynamics of P12 and beta 12 and also values of P1*, P2*, and P3*, proportional to the mean interspike intervals of N1, N2, and N3 were investigated during changes in the efficiency of synaptic connections, excitability of the neurons, and their response to afferent synaptic bombardment. It was shown that an increase (decrease) in P12 or beta 12, accompanied by a decrease (increase) in P1' and P2', is a sign of a plastic change either in the discharge frequency of N3 (not always recorded experimentally) or of the amplitudes of excitatory postsynaptic potentials of N1 and (or) N2, evoked by these discharges.