This paper describes an analysis of the effects of electric field on nerve cells by using the Hodgkin-Huxley model. When evaluating our model, which combines an additional ionic current source and generated membrane potential, we derive the peak-to-peak value, the accumulated square of variation, and Kolmogorov-Sinai (KS) entropy of the cell-membrane potential excited by 10, 100, 1 k, and 10 kHz-sinusoidal electric fields. In addition, to obtain a comprehensive view of the time-variation patterns of our model, we used a self-organizing map, which provides a way to map high-dimensional data onto a low-dimensional domain. Simulation results confirmed that lower-frequency electric fields tended to increase fluctuations of the cell-membrane potential, and the additional ionic current source was a more dominant factor for fluctuations of the cell-membrane potential. On the basis of our model, we visually confirmed that the obtained data could be projected onto the map in accordance with responses of cell-membrane potential excited by electric fields, resulting in a combined depiction of the effects of KS entropy and other parameters.

An electrophysiological experiment showed that spike timing was precise to less than one millisecond. This result indicates the possibility in the precise time codings. For a high accurate time coding, reconsideration of a neural mechanism which decides firing time is required. From such viewpoint, we quantitatively examined change in firing time with interference between two synaptic inputs through Hodgkin-Huxley (HH) and integrate-and-fire (IF) model neurons. The precise firing times in the HH model neuron were extremely different from those in the IF model neuron. In this paper, the relations of input intensity to firing time are investigated in the other more two pulse generation models: Morris-Lecar (ML) and FitzHugh-Nagumo (FN) model. The result of the ML model in a certain parameter set (type-I) exhibited monotone decreasing like that of the IF model while the result of the ML model in the otter parameter set (type-II) exhibited non-monotone decreasing like that of the HH model. The result of the FN model exhibited non-monotone decreasing like the HH model despite its qualitativeness. Next the firing patterns in the four model neurons on a model of V1 (primary visual area) and LGN (lateral geniculate nucleus) with circular and mutual excitatory connections are investigated to show how dependent on model neurons the firing patterns are. The spikes in the HH, the ML type-II, and the FN model neurons elicited synchronous oscillations while the spikes in the IF and the ML type-I model neurons did not; the firing patterns dramatically changed with the dependence on the model neurons.