Synaptic integration mechanisms. Theoretical and experimental investigation of temporal postsynaptic interactions between excitatory and inhibitory inputs

The effect of temporal activation of two closely adjacent synaptic inputs upon the postsynaptic output (voltage amplitude and time integral) is analyzed theoretically and experimentally. It is shown that (a) under certain conditions, maximal nonlinearity in the summation of postsynaptic potentials is obtained with asynchronous activation of the two synaptic inputs rather than with simultaneous activation; (b) the time integral of the voltage is more sensitive to the timing of the synaptic inputs than is the voltage amplitude; (c) an input, which by the classical definition is inhibitory, under defined conditions can and does increase the amplitude (and area) of an excitatory synaptic potential, and thus acts as an excitatory input.