Model with an adaptive spike threshold can reproduce the phasic–tonic response of ORNs to a pulse odorant stimulation. Average responses of ORNs (dashed lines) were compared with the responses of the model neurons (solid lines), i.e. the model with a constant threshold (a) and the model with an adaptive threshold (b). The unit receptor conductance was γ = 41 nS · μM−1 in (a) and γ = 99 nS · μM−1 in (b). Each spike generated by the model with a constant threshold (a) was followed by a 3 ms refractory period. The pheromone concentration in the air, Lair, was set to 0.1 pM, 1 pM, 10 pM, 100 pM for the pheromone doses 1 pg, 10 pg, 100 pg, 1000 pg, respectively. See tables and for the other parameters. (Online version in colour.)