The search for cell assemblies in the working brain.

This paper discusses why population ensemble coding by multiple neurons is a tenable view of the brain's basic neuronal code. The discussion is based on features of neuronal activity in working brains of behaving animals. The key concept to elucidate population ensemble coding is the 'cell assembly', i.e. overlapped populations of neurons with flexible functional connections within and among the populations. Recent examples of experimental approaches which indicate the cell-assembly coding of memory in the working brain are given. These experiments used a strategy that reveals two main properties of cell assemblies; the overlapping of neurons and the dynamic changes of synaptic connections in processing different kinds of memory. Several possible features of cell-assembly coding that might be explored in future experimental research are enumerated.