The Role of Inhibition in an Associative Memory Model of the Olfactory Bulb

The external plexiform layer is where the interactions between the mitral (excitatory) and granule (inhibitory) cells of the olfactory bulb (OB) take place. Two outstanding features of these interactions are that they are dendrodendritic, and that there seem to be none between excitatory cells. The latter are the ones that are usually accreditted with the role of forming Hebbian cell assemblies. Hence it would seem that this structure lacks the necessary ingredients for an associative memory system. In this paper we show that in spite of these two properties this system can serve as an associative memory. Our model incorporates the essential anatomical characteristics of the OB. The memories in our system, defined by Hebbian mitral assemblies, are activated via the interactions with the inhibitory granule cells. The nonlinearity is introduced in our model via a sigmoid function that describes neurotransmitter release in reciprocal dendrodendritic synapses. The capacity (maximal number ..