Neurons give rise to processes known as dendrites and axons that form a complex network of interconnections throughout the brain at specialized sites called synapses. Around the turn of the nineteenth century, the Italian physician Camillo Golgi (1873) developed a silver staining technique that revealed the full extent of dendritic and axonal arbors. From these images, he proposed the "reticular theory" suggesting that the neurons are not discrete cells, but instead are continuous with each other and form a syncytium. The renowned Spanish neuroscientist Santiago Ramón y Cajal (1891) used Golgi's method to reveal individual neurons in the brain and spinal cord during development and after a variety of experimental manipulations. These experiments led Cajal to conclude that neurons were discrete cells with axons ending on dendrites of different cells, a theory referred to as the "neuron doctrine." The term synapse is derived from the...