Firing time of neuron by interference between synaptic inputs

The relation of intensity of one input to firing time monotonically decreases: a strong input generates a spike faster while a weak one is slower. In reality, however, numerous synaptic inputs are gathered into a single neuron at various arrival times. In such a situation it is not easy to predict firing time. In this paper, we examine firing time by interference between two synaptic inputs through the Hodgkin-Huxley (HH) model, which is a well-studied standard model of spike activity. The relations of the intensity to the firing do not always monotonically decrease. We consider why this phenomenon occurs. The analysis indicates that the potassium current controlled by the variable n, which is the delayed rectifier, is crucial for the phenomenon. We also calculated the firing time in the case of the integrate-and-fire (IF) type model, in which such a rectifiable current does not flow, with the same input form as the HH model. All relations of the intensity to the firing time monotonically decrease. This is inconsistent with the case of the HH equations. This result casts doubt on patterns of firing time in the IF type model.