Figure 3.

Utilization of synaptic efficacy parameter determines signaling presynaptic firing rates. (A) The predicted spatially summated synaptic input from n = 500 presynaptic neurons firing Poisson trains as a function of their firing rates r. The corresponding analytical expression, derived from the model Eq. 1, reads I_post = A_SEn(rτ_inactU_SE/1 + rτ_rec U_SE). Represented are the lowest, highest, and mean values of U_SE, derived from 33 experimentally examined synaptic connections. (B) Predicted time-averaged membrane potential at different presynaptic spiking frequencies, computed from the model. Parameters: U_SE = 0.4, τ_rec = 700 msec, τ_inact = 3 msec, τ_mem = 25 msec. Superimposed are the experimental time-averaged membrane potentials from the neuron represented in C. (C) Experimentally recorded EPSPs generated by Poisson presynaptic spike trains at various frequencies. Single-sweep responses are represented. Arrows indicate the time window over which the time-averaged membrane potentials shown in B were determined. (Inset) The onset of the response to the 5-Hz Poisson spike train. Similar results were obtained from three synaptic connections.