If you are interested in these kinds of basic questions, then Copenhagen was the place to be during the last few days. Ed Lein and Rafa Yuste organized a terrific Brain Conference at the beautiful Moltke Palais, which hosted some 100 people of many different fields, all eager to work towards answering the above questions. Sparked by the fanstastic progress of single cell transcriptomics, the question that was in Petilla "Can we classify cortical neurons" has now turned into "How can we reasonably do it". The panel discussion showed the many issues still to be solved but in my opinion, this is just a matter of time.