Cortical neurons communicate in both digital and analog modes.The digital signal is the all-or-none action potential (AP) initiated first at the axon initial segment (AIS).The ability of generating APs determines the excitability of a given neuron.The analog mode of communication reflects the modulation of synaptic strength by presynaptic membrane potential.We investigated the underlying mechanism for the two modes of communication, and the role of analog signaling in regulating the balance of excitation and inhibition in the cortical network.