Recently, we have shown that in synaptically isolated pyramidal cells in entorhinal cortex layer V, repetitive application of an input can generate multiple stable graded levels of firing (Egorov et al, Nature 2002). The process depends on the stimulation of metabotropic (muscarinic, mGluR1) receptors, and the activation of a CAN current. In this work we have utilized computational modeling to elucidate possible mechanisms involved in this phenomena. We have proposed that the core mechanism is a hysteresis in the activation of kinases or phosphatases affecting the Ca-sensitivity or channel open time of the CAN-current (Fransen et al, SFN abstracts 2003). Using the model, we now study the mechanisms behind initiation of a change in level as well as the mechanisms involved in sustained activity and stability to distractors. Our simulations show that the stable graded spiking activity observed experimentally is not accomplished merely by extensive balancing of currents across an interval of voltage, as propos...