Neuronal cell types

Identifying the functionally distinct types of neuron is central to any bottom-up understanding of how the brain works. The different cell types are the brain’s elementary computational elements — the components from which the larger machine is made. We have known of some cell types for more than a century, but the coverage has been spotty and anecdotal. This is changing: it is now possible to assemble more or less complete inventories of cell types — the brain’s parts list, upon which all understandings of brain function depend. The recognition that neurons are distinct functional entities was the first great contribution of neurobiology’s founding father, Santiago Ramon y Cajal, who could make that leap because he had a method, the Golgi stain, which shows individual neurons in spectacular isolation from their neighbors. It was immediately apparent that neurons come in a florid variety of shapes and the identification of neuronal types, an industry that still flourishes, was set in motion. How are neuronal types distinguished and why do neurobiologists care so much about them?