Memory and H.M.

Memory.  What is the dictionary definition of this word?  Every person knows what it is.  Experiences and how they are stored in the brain.  There’s short-term memory, long-term memory, working memory, implicit memory, explicit memory, semantic memory… just to name a few.  This next story is a story about H.M. A man who lived for 30+ years lived with severe epileptic sesures all his life.  Doctors thought that they could perform an operation to stop his epileptic sesures.  Little did they know that what was going to happen as a result of that surgery would change the study of memory and the brain forever.

The doctors performed what is anatomically termed a bilateral medial temporal lobectomy. In layman’s terms, the bottom portions of his temporal (side) lobes, were removed toward the middle. Due to this operation, H.M.’s epileptic sesures stopped. Yes, the operation was a success. H.M.’s IQ rose from 104 to 118. However, there was one major side effect H.M. now suffered from anterograde amnesia -he could no longer form new long-term memories. H.M. could walk into a room, meet someone, turn around and stare at the wall, and them turn back around again, and re-meet that person having no recollection of the first meeting, though it happened moments before. But the story of H.M. does not stop there, H.M. was found to be able to make new memories after all; just not the ones you and I are used to acknowledging. H.M. could still learn skills, on a test called a mirror drawing test it was proven that H.M. could learn a skill of drawing a complex figure and the more times that he was exposed to this behavior, the better at it he got. He was able to learn things unconciously or what psychologists call implicitly. If you asked him to do the mirror drawing test he would admit that he had never done it before, but he could perform the task with no errors after several tries, and this could be repeated days later with improved accuracy.

Based on this evidence doctors, neroscientists, and psychologists were able to pursue memory in a new way. They realized that memory is not located in just one part of the brain. Research found that memory is located all throughout the brain; in areas that were active when the experience/task was activated. Thanks to H.M. the concept of memory changed forever. The contribution he made is still being studied today, 50 years later.