This series of articles will talk about brains that have had major influences on the advancement of neuroscience, not because they belonged to very smart people, but because they told us something new about the functioning of our brain.
What other brain could this series start with than that of H.M.? H.M was probably on the first slide of the first class I took in my neuroscience career. His brain taught us many things at once, but most importantly: where our memory is located in the brain.
Henry Gustav Molaison, shortly before his surgery.
Courtesy of Suzanne Corkin
H.M., whose real name is Henry Gustav Molaison, was born in Hartford, Connecticut in 1926. When he was about 7 years old, he started developing severe epilepsy, possibly as the result of a bicycle accident. His seizures and convulsions became so severe and frequent that he became unable to live a normal life and work his mechanic job.
At the age of 27, he was referred to doctor William Beecher Scoville, a neurologist at the local hospital who tried all possible treatments and decided that brain surgery was the only solution left. In the 1950s, little was known about the structure and morphology of the brain. People did not yet associate specific brain areas with specific functions like we do now. Dr. Scoville therefore knew nothing more than that the seizures seemed to come from the “left and right medial temporal lobes.” In the summer of 1953, he thus decided to cut these away, and removed two finger shaped pieces of tissue from H.M.’s brain.
The surgery turned out to be successful: H.M.’s seizures almost completely disappeared. A new problem had taken its place though, one that would make H.M. the biggest celebrity in neuroscience. By removing the medial temporal lobes on both sides, Dr. Scoville had completely abolished H.M’s ability to form new memories. He could tell you about the 1929 stock market crash, or World War II, but he didn’t know that he had told you that 10 minutes ago already, or what he had had for lunch that day. Everyone he met after the surgery would forever be a stranger to him, even if he would see them every single day.
For the neuroscience community this was an incredible finding. Who would have thought that all of memory formation happened in this one little area that we now call the hippocampus (Latin for seahorse)? Many scientists studied H.M. for years, among whom Dr. Brenda Milner and Dr. Suzanne Corkin. They found that H.M. was still able to learn new motor skills, such as drawing a picture when looking at it through a mirror. Another example that is especially relevant to this series is that H.M. was able to remember the names of celebrities just as well as anyone else.
This suggested that only “explicit” memories (conscious memories such as stories), but not “implicit” memories (unconscious memories such as motor skills), were formed and stored in the hippocampus. It suddenly dawned on the scientists that the brain has multiple memory systems that work in parallel with each other. Thanks to H.M., scientists have started to search for locations of other memory systems and found very different parts of the brain that support different types of learning.
Top: location of the hippocampus in the brain. Bottom: hippocampus dissected out of the brain, revealing it’s seahorse-like shape.Credit: http://www.neuroscientificallychallenged.com/blog/2014/5/23/know-your-brain-hippocampus
One last important finding was that, apart from the memory loss, H.M. remained completely himself. He was just as kind, soft-spoken and funny of a man as he was before the surgery and his IQ remained above average, despite his severe amnesia. This again shows that the brain is, at least to a certain extent, “modular”: specific brain areas are responsible for specific things. Damaging one area does not necessarily affect the other areas. This was a very important concept for the neuroscience world at that time, and is still the basis for much current neuroscience research.
H.M. lived with his mother and later with a relative until the 1980’s when he was moved to a nursing home. In 2008 he died of respiratory failure at the age of 82. His brain was moved to the University of San Diego where it was sliced one year later. The corresponding data were made publicly available to scientists by the brain observatory at http://www.thebrainobservatory.org/patient-hm-a-case-study/.
With his amnesia H.M. advanced the field of neuroscience dramatically. He will forever be stored in young neuroscientist’s hippocampi, and later –if they study hard enough- in their long-term memory systems. He will be remembered, H.M.
H.M.’s frozen brain during the cutting process in 2009.Credit: UC San Diego School of Medicine
-book: “Permanent present tense. the unforgettable life of the amnesiac patient H.M.” by Suzanne Corkin