Perception Lecture Notes: Microstimulation of the Human Brain

Professor David Heeger

In the course of surgical treatment of patients suffering from epilepsy, neurosurgions sometimes operate with the patient awake under only a local anesthetic, so that they can electrically stimulate the brain and make sure that they do not accidentally remove critical (e.g., language) brain centers. Wilder Penfield pioneered this surgical technique during the middle part of the century. In the process, he mapped out much of what we know about the organization of the human cortex. He localized specific regions of the brain involved in vision, hearing, touch, motor control, etc.

In the process of mapping out the sensory and motor areas of the brain, he stumbled upon the fact that electrical stimulation of a region of the temporal lobe produces a kind of "flashback". For example, a woman once said when the electrode touch her brain, of being in her kitchen listening to the voice of her little boy who was playing outside in the yard. She was aware of the neighborhood noises, such as passing cars, that might mean danger to him. Another patient gave the following reports while her brain was being electrically stimulated at a series of neighboring positions.

"I heard something, I do not know what it was"
(stimulation repeated at same location) "Yes, Sir, I think I heard a mother calling her little boy somewhere. It seemed to be something that happened years ago... It was somebody in the neighborhood where I live."
"I heard voices down along the river somewhere - a man's voice and a woman's voice calling - I think I saw a river."
"...in an office somewhere. I could see the desks. I was there and someone was calling to me, a man leaning on a desk with a pencil in his hand."

David Heeger