Influence of maximum firing rate of the sigmoid function on dynamic behaviors of model, showing e_g with respect to e_s for C₃ = 10 (a) and C₃ = 20 (c), [(b) and (d)] frequency distribution diagrams, e_g with respect to e_s for C₃ = 10 (e) and C₃ = 20 (f). Other parameters remain default values as listed in Table 1, and (g) effect factor K of the parameters e_s and e_g on generating limit cycle oscillation.