The Spanish anatomist Santiago Ramon y Cajal (1852-1934) explored the microscopic world of the brain and found a landscape inhabited by distinctly individual cells, later termed neurons. "The mysterious butterflies of the soul," he called them, "whose beating of wings may one day reveal to us the secrets of the mind." Although he ranks among the greatest scientists in history, the name of the Nobel Prize-winning "father of modern neuroscience" is not as well-known as that of Darwin, Pasteur, Galileo, Einstein, Copernicus, and Isaac Newton.

The second half of the nineteenth century saw a...