Before Santiago Ramon y Cajal, the scientific community viewed the nervous system as a continuous strand. Not so, theorized this future father of neuroscience, who argued that any attempt to operate on one part of the brain would disable the rest of it, like pulling out a bulb from a strand of Christmas tree lights. Cajal laid the foundation for much of what we now know about how the brain works. How did he reach such a radical finding? In Advice for a Young

—Alfredo Quinones-Hinojosa