Space-time correlations of neuronal firing related to memory storage capacity.

Most viable theories of memory require some form of synaptic modification dependent on the correlation of pre- and postsynaptic neuronal firing (which we will denote as the Hebb hypothesis). We show here that a possible consequence of this hypothesis is that the storage capacity of a network of highly interconnected neurons is related to the number of synapses and that this implies that the network can be excited into many different time sequence of firing patterns of assemblies of neurons. The important role played by the assembly (as defined by E. R. John) is discussed in detail. A modified Hebb hypothesis is proposed. The crucial experiments to test the model involve the use of two (or more) extracellular microelectrodes to record, simultaneously, the firing activity of several neurons and thus determine the spatial and temporal cross correlations after presenting a mature animal with a variety of stimuli.