Effects of spatial and temporal dispersion of synaptic input on the time course of synaptic potentials

Abstract

1. As part of the ongoing studies on the time course of single-fiber synaptic potentials recorded in spinal neurons, a theoretical analysis of the effects of spatial and temporal dispersion of synaptic input to a neuronal cable model was undertaken. 2. Results were obtained using a simple R-C soma, equivalent dendritic cylinder cable model of a neuron. Synaptic input was represented by a current injection at various points on the dendritic cable. 3. Spatial dispersion of multiple inputs to the cable model generally produced somatic transients with smooth time courses that could be closely matched by a transient generated at a single input location, usually with a different current time course. 4. Temporal dispersion, representing nonsynchronous activation of multiple synaptic contacts at the same electrotonic location, generally resulted in somatic transients with an increased rise-time and a corresponding small increase in the half-width. The somatic transient generated by these temporally dispersed inputs could usually be well matched by a single input at a different location. 5. Addition of temporal dispersion to a spatially dispersed input produced variable results in which the rise-times and half-widths of somatically recorded transients could be either increased or decreased. 6. It is concluded that a detailed knowledge of both the spatial and temporal properties of synaptic input is essential to the interpretation of single-fiber synaptic potentials. Previous results on the amplitude and time course of single-fiber synaptic potentials recorded in spinal neurons are discussed in light of the present observations.