A healthy brain maintains a harmony of neurons that excite or inhibit other neurons, but the lines between different types of cells are blurrier than researchers once thought. Introduction From Santiago Ramón y Cajal’s hand came branches and whorls, spines and webs. Now-famous drawings by the neuroanatomist in the late 19th and early 20th centuries showed, for the first time, the distinctiveness and diversity of the fundamental building blocks of the mammalian brain that we call neurons. In the ...