The restricted nature of the semantic knowledge that Henry was able to demonstrate makes it unlikely that the mechanisms he relied on for learning were identical to the mechanisms healthy adults use to acquire semantic knowledge so prolifically and spontaneously. Specifically, his ability to show any rapid learning of semantic knowledge was eliminated, presumably due to his bilateral hippocampal lesion. His only mechanism for learning was via slow-learning, in which extended repetitions of information enabled him to glean some information.33
In interpreting the results of this study, it was important to consider whether Henry’s acquisition of limited semantic information did, in fact, represent declarative learning and not nondeclarative perceptual memory—information acquired automatically through visual exposure. Henry’s learning differed from nondeclarative memory in several important respects. First, a hallmark of declarative memory is that it is accessible to conscious awareness and can be voluntarily brought to mind in words or images. In contrast, nondeclarative learning is accessible only through reenacting the task in which the knowledge was learned. Henry was able to freely recall specific details about a limited number of postoperatively famous people—John Glenn as “the first rocketeer”—or events—the assassination of John F. Kennedy. Second, the expression of nondeclarative memory is rigidly determined by the manner in which it was acquired, whereas semantic knowledge can be recapitulated flexibly in response to a variety of relevant stimuli. Henry repeatedly retrieved information about a small number of celebrities regardless of the specific language used to frame the question or the modality of the stimuli (words versus pictures). Third, Henry’s ability to generate familiar last names when he heard the first names could have been explained as an automatic stimulus-response reaction supported by nondeclarative memory. But the fact that he benefitted as much from semantic cueing about postoperative names as about premorbid names demonstrated that this new knowledge, like his preoperative knowledge, had been incorporated into a semantic network capable of supporting conscious recall. Based on this evidence, we concluded that Henry was capable of meager declarative, semantic learning. Where in Henry’s brain did this unusual learning take place? The likely candidates were the remaining bits of memory-related cortex near his lesion—perirhinal and parahippocampal cortex—and the vast cortical networks where information was stored.34
Why did Henry exhibit semantic learning about famous personalities in this study, but fail to learn new vocabulary in an earlier one? One possibility was the difference in the number and types of exposure to the stimuli. Celebrities offered a wider array of opportunities for encoding information, and Henry may have encountered the names John F. Kennedy and John Glenn on numerous occasions and in different, rich contexts. He watched the news every night from 6:00 to 7:00 p.m. and often looked at and read magazines. This variety of exposures in his everyday life may have given rise to richer and more flexible memory traces than processing the isolated words in the lab—minatory, egress, and welkin. Another possibility is that the names presented to Henry may have allowed him to take advantage, at least in some instances, of knowledge related to them that he learned before his operation. For instance, his ability to remember details about John F. Kennedy may have resulted from his knowledge of the Kennedy family acquired during the 1930s and 1940s. Similarly, Liza Minnelli had two famous parents, singer and actress, Judy Garland, and film director, Vincente Minnelli.35
Prior knowledge seemed to have helped Henry in a different kind of experiment, this one using crossword puzzles—Henry’s favorite pastime. Our experiments carried out in 1998–2000 sought answers to three questions: How proficient was Henry in solving crossword puzzles compared to healthy participants? Could he solve preoperative clues linked to postoperative events? Would his accuracy or speed increase after repeated exposure to the same puzzles? Using test materials specifically designed for Henry, we gathered additional evidence that he could anchor new semantic information to old semantic memories. We created three kinds of crosswords of twenty clues each, incorporating semantic knowledge from different time periods. One used historical figures and events known prior to 1953 with clues such as: baseball player in the 1930s who captured the home run record. We called this the pre-pre puzzle and expected that Henry would be able to solve these clues. Another had clues based on historical figures and events popularized after 1953: husband of Jackie Onassis, assassinated while president of the U.S. We called this the post-post puzzle and expected that Henry would not solve these clues. The third puzzle combined the previous two time periods by giving post-1953 semantic clues for pre-1953 answers: childhood disease successfully treated by Salk vaccine (post-1953 knowledge); answer: polio (pre-1953 knowledge). We called this the pre-post puzzle and thought that Henry had a good chance of putting his old knowledge to work during the course of solving it. Henry’s instructions were to complete each puzzle in any manner he liked, and he was allowed to erase answers. We did not impose a time limit but asked him to tell us when he had finished each one. Henry completed the same three puzzles once a day for six consecutive days. Each puzzle was presented only once on a given day, and he had a short break before beginning the next puzzle. At the end of each test session, the examiner showed him the correct answers. Henry corrected any misspelled words and inserted the correct answers where he had left blanks.36
We were curious to see whether the repeated exposures to the correct words on the third puzzle—combining pre-1953 clues with post-1953 answers—would engage Henry’s semantic network of pre-1953 knowledge to the point where he would eventually fill in the correct answers. We believed this was a real possibility because our previous evidence showed that occasionally he could engage his existing mental schemas to acquire new facts (JFK was assassinated). On the pre-1953 puzzle, Henry responded with high accuracy and performed consistently well. But he regularly missed the two most difficult clues, Chaplin and Gershwin, and his overall score did not improve across the six days of testing. On the post-1953 puzzle, he was, not surprisingly, very inaccurate, and again his performance did not improve over six days. In marked contrast to the absence of learning on the pre-pre and post-post puzzles, however, Henry did show improvement across five days of testing with the pre-post puzzle because he could link the new information to mental representations established before his operation. He successfully learned to associate the postoperative knowledge with preoperative information for six answers: polio, Hiss, Gone with the Wind, Ike, St. Louis, and Warsaw. This improvement is consistent with the general idea that new semantic learning in amnesia is facilitated when the information is meaningful to the individual patient, something that the person can relate to.37
In the crossword puzzle experiment, Henry demonstrated an ability to learn the solutions to puzzle clues that allowed him to benefit from preoperative knowledge. This same mechanism—linking postoperative to preoperative knowledge—was at work when he told us facts about some of the celebrities whose names he recognized as famous. He was able to encode, consolidate, store, and retrieve a small amount of information about famous people—knowing that John F. Kennedy “became president; somebody shot him, and he didn’t survive; he was Catholic.”38
The concept of mental schemas sheds an interesting light on Henry’s unexpected ability to consolidate and retrieve the occasional piece of new semantic knowledge. Sir Frederic Bartlett, a British philosopher who became an eminent experimental psychologist, introduced the concept of schemas in 1932. Based on his studies of memory performance in healthy research participants, Bartlett wrote, “Remembering is not the re-excitation of innumerable, fixed lifeless and fragmentary traces.” Instead, he viewed remembering as an active process—the capacity to creatively rebuild your inner representations of the world. He named these organized, constantly changing masses “schemata.” As Henry was trying to solve the pre-post crossword puzzles, he may have been relying on an enduring structured representation of old knowledge—a schema—to understand, store, and recall the
new information.39
When we watch a political debate, we see the candidates presenting details about their policies and how they will implement them. As the questions and answers unfold, we feed the new information into a mental framework that allows us to understand, evaluate, and consolidate each candidate’s ideas. Some time later, prior to election day, we can consult our updated mental schema and make an informed decision about whom to vote for. We are able to make our choices efficiently because we have stored the relevant semantic information in an organized body of knowledge. Henry retained mental schemas established during the years before his operation, and occasionally he was able to tap into them to anchor a few new facts.
In 2007, neuroscientists at the University of Edinburgh conducted experiments on schema learning in animals. They trained normal rats to associate distinct food flavors with specific locations in a small arena that was familiar to them. Initially, the rats formed six flavor-place associations. By trial and error, they learned, for example, that rum-flavored food pellets were in one location, banana-flavored pellets in another, and bacon-flavored pellets in another. There were six sand wells where the rats could dig for their reward. During learning, the animals were cued with a specific food in the start box, and their task was to find the well that contained the same food (cued recall). If they dug in the correct sand well, they were rewarded with more of the cued food. After several weeks of training, the animals acquired associative schemas for this task—they mapped each flavor to a specific sand well in the arena.40
The researchers then asked whether having this schema would facilitate the encoding and consolidation of new flavor-place associations and their rapid integration into the existing schema. They closed two of the sand wells and introduced two new ones with two new flavors. The rats received just one rewarded trial with each of the two new pairs and then rested for twenty-four hours. When the researchers tested their memory for the two new flavor-place associations, the rats chose to dig at the correct locations and not at the closed ones. They learned the new pairs in a single trial and remembered them for twenty-four hours, indicating that the earlier learning of the associative schema helped in this process. After another twenty-four hours, the researchers gave the rats hippocampal lesions. When they recovered from the operation, the rats still recalled the location of the original schema and, amazingly, the two new pairs. The new associates had been quickly consolidated and stored outside the hippocampus, probably in the cortex. Apparently the rats had learned an associative schema incorporating the mapping of flavors to places in the arena, and this schema provided a framework to help them retain the two novel paired associates.41
During the twenty-seven years before his operation, Henry had successfully built up numerous schemas and stored them in his cortex. Even though his medial temporal-lobe lesion prevented him from learning new associations, like cabbage-pen, he could sometimes fall back on a reservoir of schemas he had consolidated before his operation and had retained in his long-term memory. For instance, when solving the pre-post crossword puzzle, he correctly responded with polio, Hiss, Gone with the Wind, Ike, St. Louis, and Warsaw, and this learning may have relied on his preoperatively acquired schemas. This kind of organized, stored information may be what enabled him to consolidate a few new facts after his operation. What he saw and heard on television may have activated and updated longstanding schemas related to politicians, movie stars, and technology, enabling him to remember JFK, Julie Andrews, Lee Harvey Oswald, Mikhail Gorbachev, and to define Skylab as “a docking place in space.”
How did Henry’s capacity to learn fragments of general knowledge affect his everyday life? My guess is that his sense that he knew a few people at Bickford, and his ability to recognize a name here and there, gave him the feeling that he was among friends. In 1983, when he returned to Bickford from MIT, a staff member noted that he appeared happy to be back and seemed to remember his companions. When he watched television, some of the news anchors and actors in sitcoms must have looked and sounded familiar, so he could relate to them as his TV buddies. Henry acquired factual knowledge about his nursing home: the layout of his room, the lounge, and the dining room, the dog who sat by his wheelchair, the woman who flirted with him, and the numerous aides who cared for him. Although his interactions with the world were far from normal, his life did have familiar attachments that helped him feel secure. Overall, in spite of his tragedy, Henry got along.
We have numerous, attention-grabbing examples of Henry’s ability to acquire snippets of novel semantic knowledge after his operation. Still, his consistent impairment compared with controls made it clear that the surgical removal of his medial temporal-lobe structures in 1953 had decimated his ability to acquire a significant amount of new semantic information. In spite of this gap in his knowledge, however, he was capable of thinking about his personal world and communicating effectively. He had an excellent vocabulary and an impressive knowledge of world events and celebrities, but this knowledge was frozen in time, an archive of information from the first half of the twentieth century.
Twelve
Rising Fame and Declining Health
After the publication of Scoville and Milner’s 1957 paper “Loss of Recent Memory after Bilateral Hippocampal Lesions,” Henry gradually became famous within the neuroscience community. His story began to appear in psychology and neuroscience textbooks in 1970, and by the 1990s was invoked as a case study in nearly every textbook that addressed memory. In scientific papers, he was frequently highlighted as the inspiration for particular experiments. Every young psychologist and neuroscientist learned about H.M. in school, and the description of his amnesia was a touchstone for the severity of memory impairment in other patients. Through our continued research with him, Henry became the most comprehensively studied patient in neuroscience.1
By the late 1970s, I had become Henry’s primary point of contact for anyone who wanted access to him for research. Hans-Lukas Teuber died in 1977, and Brenda Milner moved on to other research topics, while still maintaining a strong interest in Henry. I had inherited him as a patient. He lived only two hours away from MIT, so it was logistically easy for him to visit my lab or, as he grew older, for my colleagues and me to visit him at Bickford.
Over the years, a number of researchers came to MIT to test Henry for their own studies, but I felt strongly that Henry should not be made available to every person who wanted to meet him. If I had opened the gate, allowing all interested researchers to test and interview him, the resulting free-for-all would have been a constant drain on his time and energy, and would have taken unfair advantage of his memory impairment and willingness to be helpful. Many people were eager simply to talk with Henry, but I did not want him to become a sideshow attraction—the man without a memory. I, therefore, required any investigator who wanted to study Henry to visit my lab first and present the proposed research protocol at our weekly meeting. I wanted to make sure that the experiments were well designed, so that the data from Henry would generate meaningful conclusions. My requirements may have frustrated some, but they spared Henry from being besieged by frivolous inquiries.
From 1966 onward, 122 scientists had the opportunity to work with Henry, either as members of my lab or as our collaborators from other institutions. Together, we investigated a broad range of topics. A memory researcher from the University of California, San Diego, came to study Henry’s semantic knowledge. A vision scientist at the Rowland Institute in Cambridge, Massachusetts, examined an aspect of visual perception in Henry and a group of Alzheimer patients to find out whether memory impairment affected performance on a visual after effects task. A neuroscientist came from the University of California, Los Angeles, to conduct EEG recordings while Henry detected different targets on a screen.
Although every visiting scientist had read extensively about Henry and his case, some still found the experience of meeting him in person astounding. One colleague, Richard Morris, recalled meeting Henry with a group of h
ippocampus researchers. Later, he wrote this note to me describing the event:
We sat in a room, and he came along, and we met him. In many respects, he was exactly as you had described him in papers—very courteous, very polite. Initially, the conversation was such that you had no reason to think there was anything at all untoward. This was just like meeting a very kindly, genial old man, really. But then gradually one or two things happened, various repetitions of things that began to reveal that there was something untoward.
The opportunity arose for one of us to leave the room, and it actually was I. We’d been talking maybe for a half an hour or so, and then I got up and left the room and deliberately stayed out of the room for about ten minutes and then rejoined the conversation. It was very striking because my colleagues introduced me to him again and he said, “Nice to meet you,” as if he hadn’t known that I’d been there before, and then pointed to an empty chair and said, “There’s an empty chair. You go sit there.” And this, of course, had been the chair I’d been sitting in before. So that was exactly as we’d been led to expect from the published literature, but to see it with our own eyes was interesting.
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