How do cell assemblies encode information in the brain?

The present review discusses why cell-assembly coding, i.e. ensemble coding by functionally connected neurons, is a tenable view of the brain's neuronal code and how it operates in the working brain. The cell-assembly coding has two major properties, i.e., partial overlapping of neurons among assemblies and connection dynamics within and among the assemblies. The former is the ability of one neuron to participate in different types of information processing. The latter is the capability for functional synaptic connections, detected by activity correlations of the neurons, to change among different types of information processing. An example of a series of experiments which detected these two major properties is then given. Several relevant points concerning the detection of the actual dynamics of cell-assembly coding are also enumerated. They include the dependence of the type of cell-assembly coding on types of information-processing in different structures of the brain, sparse coding by distributed overlapped assemblies, and coincidence detection as a role of individual neurons to bind distributed neurons into cell assemblies.