For more than 50 years, he's lived without major portions of his brain. Yet at 79, H.M., as he is known in the literature, continues to be a research dream-come-true.
"No one person seems to have contributed more to our understanding of human memory than H.M.," says Brian Sotko, a medical student at Harvard University who has been studying H.M.'s cognitive capabilities.
Because of radical 1953 surgery to stop intense and uncontrollable seizures, H.M. is the only patient alive today who has had a near-complete removal of the hippocampus, amygdala and surrounding cortex on both sides of his brain. After the surgery, the seizures were infrequent, but he lost his ability to remember new facts about people, places or things after a few seconds--a condition called anterograde amnesia.
Over the years, neuroscientists have learned via H.M. how these brain regions help form memories. And he's still helping. Skotko, who began his research while an undergraduate at Duke University, teamed up with Duke and Massachusetts Institute of Technology (MIT) neuroscientists to assess whether H.M. could learn more than was initially thought. The findings, published last November in the APA journal Neuropsychology (Vol. 18, No. 4, pages 756-769) were surprising to Skotko, who says it appears that, "H.M. was able to acquire new semantic information that we would not have expected for someone with profound anterograde amnesia."
Because H.M. does crossword puzzles daily, Skotko and his colleagues constructed crosswords with clues that relied on worldly knowledge H.M. acquired prior to his 1953 surgery and used them as anchors to which H.M. could learn from clues referring to events since 1953--for example, that John F. Kennedy became president and was assassinated (JFK was a well-known political figure prior to 1953).
H.M.'s crossword-puzzle performance revealed that he was able to learn new facts about well-known post-1953 people, places and events. "We suggest that H.M. might be using his residual posterior parahippocampal gyrus to support his learning," says Skotko.
The findings confirm those of more traditional cognitive tests conducted a few years earlier at MIT. After graduate students Gail O'Kane and Elizabeth Kensinger taught H.M. about people who became famous after his surgery, he recalled--given fact clues--23 out of 35 celebrity last names. In forced-choice recognition, H.M. not only differentiated 87 percent of the post-1953 famous names from names pulled from the phone book, but, remarkably, volunteered unique identifying facts for about a third, describing John Glenn as "the first rocketeer" and saying Julie Andrews was "famous for singing on Broadway."
"I've known H.M. since 1962, and he still doesn't know who I am," notes MIT neuroscientist Suzanne Corkin, PhD, a longtime H.M. researcher who directed the research. Nonetheless, she says, H.M. may have picked up the knowledge about famous people from watching television, reading the paper, doing puzzles and so on. The MIT report, published in 2004 in the journal Hippocampus (Vol. 14, No. 4, pages 417-425), concludes, "The results [provide] robust, unambiguous evidence that some new semantic learning can be supported by structures beyond the hippocampus proper." Corkin thinks H.M. may be tapping his intact perirhinal and parahippocampal structures, which may work as a team with some cortical areas as well.
H.M. seems to know that he is helping science. Says Skotko, "He has been known to say, 'What they learn about me will help them to help others.'"