3 state neurons for contextual processing

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 several brainareas which might be explained by our model. The interactions betweenthe two kinds of inputs lead us to suggest that some neurons may operate in 3 states: disabled, enabled and firing. Suchenabled, 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 processing andresponse variability. 1 Introduction Excitatory interactions between neurons are mediated by two classes of synapses: AMPA and NMDA.