Cell assemblies in the rat CA3 recurrent network: do we really need oscillations?

Abstract:
The concept of cell assemblies implies :
(1) recruitment of interconnected neurons (which synaptic weights are to get reinforced); (2) time limits (to switch from one assembly to the next, the circuit needs to define when the assembly starts and stops, like the spaces allow us to know when we switch from one word to the next in a sentence); (3) size limits (we don't want seizures).

I will present recent data suggesting that the basic organization of the hippocampal CA3 circuit meets the above three requirements because during spontaneous activity in vivo, a recurrent excitatory/inhibitory loop operates at a time scale of 10ms, providing successive collective bursts between interconnected neurons separated by full interruptions of neuronal activity. As a consequence, even in absence of oscillation in the circuit, the spike flow from the pyramidal cell population is sparse, being constantly interrupted. We speculate that this basic circuit organization, which can be rhythmically recruited during network oscillations, underlies the formation of hippocampal cell assemblies.

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