Neurons receive excitatory inputs via both fast AMPA and slow NMDA type receptors. We find that neurons receiving input via NMDA receptors can have two stable membrane states which are input dependent. Action potentials can only be initiated from the higher voltage state. Similar observations have been made in sev(cid:173) eral brain areas which might be explained by our model. The in(cid:173) teractions between the two kinds of inputs lead us to suggest that some neurons may operate in 3 states: disabled, enabled and fir(cid:173) ing. Such enabled, but non-firing modes can be used to introduce context-dependent processing in neural networks. We provide a simple example and discuss possible implications for neuronal pro(cid:173) cessing and response variability.