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A job for the hippocampus

Imagine never having a new memory

When the hippocampus stops working you stop creating new memories

It's thought that the process of writing a working memory into the long-term memory store is largely controlled by a seahorse-shaped set of neurons in the brain called the hippocampus.

How and where do we store our memories? How do we learn new information and commit it to memory? Is there just one area that controls memory or many? Science had plenty of questions but no answers until the remarkable case of the patient known as H.M. entered the literature in 1953.

H.M. - the most famous patient in psychology?

H.M. had been deeply troubled by epilepsy since his teens. At the age of 27, doctors, attempting to cure him of his seizures, operated and removed certain parts of the brain, including it was later discovered, a little-understood structure called the hippocampus.

On one level the operation was a success - the seizures which had never responded to medication, were now controllable. But the operation left him unable to form new memories. Medically speaking he was suffering from severe anterograde amnesia - the inability to put new information into long-term memory. Unwittingly, H.M. would become one of the most important figures in modern-day neuroscience and a doorway to the mysteries of memory.

For more than half a century, people have written about H.M.'s condition but perhaps the most straightforward description of his problem comes from Brenda Milner, the first psychologist to study him. She wrote that H.M. appeared "to forget the events of daily life as fast as they occur".

What H.M lacked was not a working memory (sometimes called short-term memory) - he could remember a phone number for a few seconds, provided he was not distracted, after which it vanished. He could also recall most events prior to the operation and his childhood memories were intact. Neither was his IQ affected. What H.M. lacked was the ability to commit anything new to memory. A more recent study of him concluded that "he doesn't know his age, the current date, nor where he is living … he does not know his own history". Each time his doctors would enter the room, they would have to reintroduce themselves as would anyone who wasn't associated with the time before his operation.

No patient in the history of neurology has been more closely studied and yet, in spite of his condition, H.M. has always been happy to cooperate with scientists (even now in his 80s). His story has profoundly changed our scientific understanding of the brain. For one thing, it was made startlingly clear that new memories and old memories aren't controlled by the same part of the brain. His deficit also suggested that forming long-term memories requires at least a two-stage process and that the first stage somehow involves the area which the surgeons cut out of H.M., the hippocampus (part of the temporal lobes - bits of the brain found behind and slightly above your ears). At some later stage however, memories get transferred over to another part of the brain, perhaps all over it? Today these initial discoveries remain fundamental to memory research.

The case of H.M is not unique but not many people have suffered such profound amnesia. One who has is Clive Wearing, a former music producer for the BBC and an accomplished choirmaster. He's also been the subject of at least two TV documentaries. Admitted to hospital in 1985 with severe encephalitis (swelling in the brain) he developed an infection, fell into a coma and suffered damage to his hippocampus. Like H.M., Wearing is unable to acquire new memories but it's his emotional state that brings home just what living with this condition is like. His wife recently wrote a book which describes the horror of life without a memory as well as the difficulty of caring for someone like Clive who's life he himself describes as "like being dead".

YOUR COMMENT

Mary Haight
Oliver Sacks' 'Lost Mariner' in THE MAN WHO MISTOOK HIS WIFE FOR A HAT is another interesting example.

Mary
When I saw the programme about Clive Wearing I suddenly realised that his problems were very similar to mine. After years of living with fear of the unknown for the first time I was aware that I was not the only one suffering an unexplained loss of memory.I have since heard of some others and though we don't all have exactly the same problems it is a help to know you are not alone and going mad. The medical profession at times can be quite dismissive of the problem.

Neuroscientist
The damage to patient H.M. brain encompasses more of the medial temporal lobe than the hippocampus alone. Also working memory is different from short term memory.

psychmonkey
The film Memento has a central character who may (or may not) have brain damage. He has a condition similar to H.M called anterior retrograde amnesia and cannot form new memories. The film begins at the end and ends at the beginning. It gives an insight into what it must be like to have this form of amnesia. Check out the blog contemporarymottledsheep for an outline of the neuroscience of anterior retrograde amnesia and links to articles on memory loss at the movies.

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