Wilder Penfield

The neurosurgeon who mapped the human cortex in awake patients, gave us the 'homunculus', and built the Montreal Neurological Institute.

Wilder Penfield (1891–1976) was an American-born neurosurgeon who became a Canadian citizen. A Rhodes Scholar who studied under Charles Sherrington at Oxford, he founded the Montreal Neurological Institute in 1934, combining a hospital and research centre — a model for neuroscience institutes since.

The Montreal procedure

Penfield specialised in surgery for epilepsy that didn't respond to drugs. Because the brain itself has no pain receptors, operations can be done with only local anaesthetic of the scalp, with the patient awake. Before removing tissue, Penfield stimulated the exposed cortex with a weak electrical current and asked the patient to report what happened. That let him locate the source of seizures and avoid damaging areas critical for speech or movement — the Montreal procedure. Versions of it are still used for epilepsy and tumour surgery today.

The homunculus

Over hundreds of operations, Penfield and his colleagues (Edwin Boldrey, then Theodore Rasmussen) mapped the strip of motor cortex that moves the body and the neighbouring somatosensory cortex that feels it. Each body part had its own patch, arranged in order from toes to tongue — with huge areas for the hands, lips and face. They drew the result as the homunculus, a distorted "little man" with giant hands and lips.

Memories on demand?

Stimulating the temporal lobes sometimes triggered vivid experiences — a familiar song, a scene from the past. Penfield took these as replayed memories. Later researchers have been cautious: such experiences were rare, often dreamlike, and may be reconstructions rather than recordings.