The phase diagram of the coupling systems under (a) t_s = 20 s, (b) t_s = 20.01 s. (a) At the beginning, the neuron is in the state of discharge (black). At 20 s, the external stimulus is removed (turquoise), and the neuron cannot continue to fire and return (red) to the resting state (green). (b) At first, the neuron is in the state of discharge (black), At 20.01 s, the external stimulation is removed (turquoise), and the neuron continues to discharge and “delay” appeared (red). After that, “delay” ends (magenta) and the neuron returns (blue) to the resting state (green).