http://www.sciencemag.org/news/2021/06/newly-detailed-nerve-links-between-brain-and-other-organs-shape-thoughts-memories-and

In the 1930s, neurosurgeon Wilder Penfield pioneered a daring new kind of cartography. As a stenographer took notes, he delicately touched an electrode to the exposed brains of his awake, consenting patients and asked what they felt as electrical current hit different areas.

Penfield wanted to better predict which brain functions would be threatened when surgeons had to remove tumors or chunks of tissue that were triggering epileptic seizures. Stimulating adjacent brain regions, he found, produced sensations in corresponding body parts: hand, forearm, elbow. The result of his mapping was the iconic “homunculus”: a map on the brain’s wrinkled outer layer representing the surface of the body.