The challenges in objectively determining the size of the assembly, neuronal word or sentence, which can lead to an observable output, include not only recording large numbers of neurons simultaneously but also determining the critical brain areas, cortical layers and neuron types which are most relevant in producing the desired output. Adding more neurons from structures not critical for the task would artificially reduce the estimated fraction of participating cells. Finally, if the network in which the assembly is embedded has scale-free features, the assembly size may scale with the network, rather than represent an ‘optimal’ size (Sporns et al., 2010). To date, we can only tentatively conclude that even a small cell assembly in the cortex likely involves tens to hundreds of pyramidal cells and their transient partner interneurons but the exact size depends on the required accuracy of the goal. It appears then that while the cell assembly can be conceived of as a large philharmonic orchestra in which the contribution of each instrument is needed to perform a perfect concert, a small fraction of key assembly members can play a ‘good enough’ recital.
