Hebb published the idea of Cell Assemblies (CAs) in 1949, and it's largely agreed that we have them.
If you have a concept, say cat, it is represented by a CA.
CAs are thus central to neuropsychology, and biological cognitive architectures.
CAs are sets of neurons that can fire persistently, are learned, fire synchronously, and are each a relatively small subset of all the neurons.
The problem is that our models using simulated neurons do not do a very good job of implementing CAs.