What physical changes occur within an organism's body when it sees, hears, smells, tastes, or feels some outside stimulus? That question has intrigued scientists for at least a century. By the early 1870s, some initial answers to the puzzle had begun to appear. Research showed that an electrical impulse causes heart muscle to contract in an "all-or-nothing" manner. That is, after stimulation, the muscle either responds in a specific manner independent of the stimulus's intensity and frequency or not at all. By the turn of the century, the all-or-nothing response was shown to be characteristic of all smooth muscle. This research also suggested that neurons (nerve cells) might behave similarly to muscle cells.

Confirmation of this view was provided over the next two decades by the work of a number of scientists, particularly by that of Edgar Douglas Adrian. Adrian was born in London, England, on November 30, 1889. He...