Friday, December 4, 2009

A memorable amnesiac

When little Henry Molaison was 7 years old, he fell off his bicycle. Little did he know that this event was possibly the first link in a chain of events that eventually made him the most famous patient in the history of neuroscience.

Sometime after his bicycle accident, Henry started having seizures. At first they were just little seizures. Then, when he was 16, he had his first major seizure, and it all went downhill from there. Unable to hold a job and not responding to the anticonvulsant drugs that were available, Henry and his family considered a brain operation. His surgeon, Dr. Scoville, wanted to try a new experimental type of surgery, and Henry went for it. So in 1953, when Henry was just 27 years old, he got both his medial temporal lobes removed (kind of like a lobotomy, but instead of removing the front of the brain, they removed part of the sides, just about at the level of your ears).

The operation was extremely successful: the seizures stopped! Unfortunately, this happy outcome was overshadowed by a very strange “side effect”: Henry now suffered from severe anterograde amnesia, meaning he could no longer form new memories. He also suffered from retrograde amnesia: he could not remember events from three to four days prior to the operation, and other events from a more distant past. But the anterograde amnesia was the most astonishing. You could have a conversation with Henry, then leave the room for a few minutes, and when you came back, it was as if he had never met you. Can you imagine?

Dr. Scoville called on one of his friends, Dr Penfield (that’s right, Wilder Penfield, from MontrĂ©al!) who then sent his graduate student, Brenda Milner, to study Henry. Even after all that had happened to him, Henry remained a friendly guy and was okay with being studied extensively. The knowledge we gained from Henry (known as H.M. until his death to preserve his anonymity) laid the foundations for much of what we know today about memory (which, I agree, isn’t all that much, but still). For example, prior to Henry, it was thought that memories formed all over the brain. Studying him taught us that instead it is the hippocampus, a part of the brain that was removed during his operation, that is crucial in forming memories. Studying Henry also taught us that there are multiple memory systems, a most unexpected discovery. While Henry couldn’t remember what he had for breakfast 10 minutes ago, he could learn a new task, like drawing a star while only looking at his hand in a mirror (do try this at home to understand the challenge it represents). He would get progressively better and faster at it but never remembered doing the task before. This went on until one day he drew the star and exclaimed: “This was much easier than I thought it would be!”. This lead to the notion that there are different types of memory such as declarative (conscious knowledge of facts and events) and procedural (skill-based knowledge).

The reason I’m bringing up Henry today is because this week, one year after his death, neuroscientists at UCSD started slicing up Henry’s brain in extremely thin slices. These slices will be available for scientists all over the world to look at, analyze and study. Even though he’s gone, there is no doubt we still have much to learn from the most famous neuroscience patient.

Reference: The legacy of patient H.M. for neuroscience (2009) Squire, L. R. Neuron 61(1):6-9

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