Nucleus accumbens medium spiny neurons display a two state membrane potential controlled by active channels and synaptic input. Inward rectifying potassium (KIR) channels play a major role in maintaining one of the states, the hyperpolarized down state. The KIR currents in 60% of these neurons are non-inactivating whereas in the remaining, they inactivate . The significance of this difference is unknown. We describe a computational study comparing the biophysical properties of medium spiny neurons possessing these two types of currents.