25. Sir Henry Head
Sir Henry Head was a 19th-century British neurologist who spent most of his career studying the concept of nerve damage and the regaining of sensation. His obsession with nerves and their recovery led him to begin experimenting. He felt his patients were not describing their pain and overall nerve sensations in enough detail, therefore, Head chose to begin using himself as a test subject.
In 1903, Head had the radial nerve in his left arm surgically severed, with a section removed and the remaining halves stitched together. Over the course of three months, sensation slowly returned to his arm, and he was able to feel pain again. This study eventually led to mapping out the nervous system and its healing properties and how the human brain can process different sensations.