From images to physiology: A strange paradox at the origin of modern neuroscience

In 1873 Camillo Golgi published an article that contained the description of entire nerve cells stained in black with a new histological procedure, the black reaction. He subsequently organized all the observations made with this method in a book published in 1885. On the basis of these studies, Golgi developed a physiological model of the brain that was influenced by a holistic conception he had in mind. He named this theory diffuse nervous network, assuming that the axonal prolongations were fused (or intimately interlaced) in a diffuse web along which the nervous impulse propagated. One of the scientists who quickly understood the importance of Golgi's results was the Spanish anatomist Santiago Ramón y Cajal. However, when he studied the brain with the black reaction, he had in mind the idea of the nerve cells as independent "units" (named neurons by Waldeyer, 1891). Thus Ramón y Cajal quickly became the champion of the neuron theory that paradoxically developed thanks to the same black reaction used by Golgi for the formulation of the opposite diffuse nervous network theory. The controversy between Golgi and Ramón y Cajal represents a dramatic instance of a theory-driven perception of the same morphological evidence.