The three potent neurotransmitters dopamine, norepinephrine, and serotonin were known to science prior to the 1960s, but the precise structure and extent of their nerve cells was unclear. Annica Dahlström and Kjell Fuxe used the novel technique of histoflourescence to map the pathways that released them into the brain in a landmark paper in 1964, “Evidence for the existence of monoamine neurons in the central nervous system“. The field exploded, and strange facts emerged. They are greatly outnumbered, as our brain only holds a million or so of them. But they exert a huge influence over the remaining billions of other nerve cells, fanning out into up to 500,000 nerve endings connecting to hundreds of other distant cells.