Permanent Present Tense

by Suzanne Corkin

  The CRC became a home away from home for Henry; the CRC staff and the many researchers who passed through our lab became his extended family. Henry was admitted to the CRC for testing fifty-five times from 1966 to 2000. He sometimes stayed for three weeks or a month when lab members administered a spectrum of learning tasks that required several consecutive days of training.

  Henry traveled to and from the CRC by car, with myself or another MIT researcher driving. A second person always accompanied the driver in case Henry had a seizure or some unforeseen event occurred. On these two-hour drives, he passed the time looking out the window, and sometimes the pictures on billboards triggered monologues that recurred from trip to trip.

  Howard Eichenbaum, a collaborator from Wellesley College, recalls one such trip in 1980 when he drove to Bickford, Henry’s nursing home, to transport him back to the MIT CRC. On the way there, Eichenbaum pulled into McDonald’s for lunch, and returned to his car with a cup of coffee. When he arrived at Bickford, he went inside, talked with a staff member, and escorted Henry outside to his car. With Henry comfortably seated in the back seat, they set out for Boston. After a few minutes, Henry noticed the coffee cup on the dashboard and said, “Hey, I knew a fellow named John McDonald when I was a boy!” He proceeded to relate some of his adventures with the friend; Eichenbaum asked a few questions and was impressed by these elaborate childhood memories. Eventually, the story ended and Henry turned to watch the scenery passing by. After a few more minutes, he looked up at the dashboard and remarked, “Hey, I knew a fellow named John McDonald when I was a boy!” and proceeded to reproduce virtually the identical story. Eichenbaum again asked probing questions in an effort to continue the interaction and to determine whether the facts of the story would be the same. Henry was unaware that he was recounting the tale almost verbatim. After a few minutes, the conversation ended, and he turned to view the scenery again. Just minutes later, Henry again looked up to the dashboard and exclaimed, “Hey, I knew a fellow named John McDonald when I was a boy!” Eichenbaum helped him reproduce the same conversation yet again, and then quickly disposed of the cup under his seat.4

  The nurses and kitchen staff at the CRC all doted on Henry. He had a private room with an adjoining bathroom, and every morning the nurses would wake him and help him get ready for breakfast. Around nine, he would begin testing in one of the well-equipped testing rooms down the hall. We would typically conduct multiple studies in parallel, with different lab members giving different tests in alternate sessions. So as not to tire Henry out, we gave him frequent breaks, often stopping for cookies and a cup of tea in the afternoon. The CRC dietitian and her staff served him homemade meals, preparing his favorite foods, such as French toast and cake. His only dislike was liver. Over the years, Henry—always a large man—grew a substantial belly, and though the dietician reined in his caloric intake, she always allowed him dessert. After lunch and in the evenings, he went to the lounge where he socialized with the other research participants, worked on puzzles, and watched movies.

  In this ideal research environment, my colleagues and I had the wonderful opportunity to investigate the strengths and deficiencies of Henry’s intellect. An early focus was on his perceptual capacities. Perception and memory are linked in that the information we perceive through vision, hearing, touch, smell, and taste provides the raw ingredients for our memories. All sensory modes contribute to memory formation, so we wanted to rule out any basic perception problems as culprits for Henry’s poor memory. During his first admission to the MIT CRC in 1966, part of our plan was to extend the examination of his vision and hearing with greater precision than had been done in previous clinical neurological examinations. Brenda Milner came down to MIT from Montreal, and with the help of my colleague, Peter Schiller, we administered a broad spectrum of tests over the course of Henry’s seventeen-day stay.

  To confirm that Henry could see all areas in his visual field—those straight ahead, up, down, and off to each side—we asked him to place his chin on a chin rest and stare at a point directly ahead inside a bowl-shaped instrument. His task was to push a button each time a tiny light flashed in different parts of the bowl, while keeping his eyes glued to fixation point. With this method, we found that Henry’s field of view was normal in all directions.

  In a test of visual perception, masking, Henry saw a large letter on a screen followed immediately by a mask that covered the letter and stopped processing of the letter in Henry’s visual circuits. The key measure was how much exposure time he needed to name the letter. In a second task, metacontrast, Henry saw a solid black circle for ten milliseconds and then, for ten milliseconds, a larger black doughnut whose inner edge touched the outside of the circle. If the circle and doughnut were flashed at the same time, Henry saw the two separate stimuli combined into a single large black circle. But if they were flashed one after the other with a tenth of a second between them, the circle disappeared and Henry saw only the doughnut. When the interval between the circle and the doughnut was increased to a second, Henry perceived the circle and doughnut as separate objects. Here the critical measure was the time that elapsed between the circle and the doughnut for Henry to see them as two separate objects. On both measures of visual perception, masking and metacontrast, Henry’s performance again resembled that of control participants.5

  We next tested Henry’s ability to perceive more complex stimuli, such as faces and objects. We showed him forty-four black and white patterns, each suggesting a face. He responded quickly and accurately when asked to judge the sex and approximate age of each person. On another task, he had no difficulty identifying sketchy drawings of twenty objects (see Fig. 4).6

  To assess Henry’s hearing, we seated him comfortably inside a sound attenuated booth and asked him to wear headphones though which we could present tones to one ear or the other. He held a device with a button and depressed it when the tone came on and released when it went away. We placed written instructions in front of Henry, so he always knew what to do. A very faint, inaudible tone would come on and slowly become louder. As soon as Henry heard the tone, he pushed the button. Then the tone would gradually become softer, and Henry pushed the button when he could no longer hear it. By repeating this procedure at several sound frequencies, we showed that Henry’s hearing was normal from low to high frequencies.

  Establishing the integrity of Henry’s sense of touch was trickier because many years of taking Dilantin had left him with a peripheral neuropathy—sensory loss restricted to the parts of his body that are covered by gloves and socks. On formal testing, he showed decreased sensitivity in these areas, but he could still identify common objects by touch and could appreciate the shape of patterns perceived with his hands well enough to construct replicas when given the necessary blocks to do so.

  The exception to Henry’s preserved sensory capacities was his sense of smell. Around the world, people delight to the smell of freshly baked bread, but after his operation, Henry could not enjoy, and therefore record, this heavenly sensation. The hippocampus does not support the sense of smell (olfaction), but several structures adjacent to the hippocampus do. When we inhale the smell of fresh-out-of-the-oven bread, we activate neurons that transfer olfactory information from the nose to the brain’s major receiving areas for this sensation. These areas include the front part of the parahippocampal gyrus, part of the amygdala, and the cortex around the amygdala. Scoville’s operation report indicated that he removed these key olfactory areas from Henry’s brain. The operation spared other primary olfactory areas in the frontal lobes, so in 1983, we conducted several experiments to determine whether these parts of the brain, still intact in Henry, could support any olfactory perception.7

  To test Henry’s sense of smell, we asked him to sniff bottles containing a common odor such as coconut, mint, or almond, and to select the name of the odor from five choices written on a card in front of him. Although this was not a memory test, the only choice he got correct was distilled water; when he
sniffed that bottle, he responded, “Nothing.” His performance showed that he could detect the presence of an odor normally—odor versus no odor—but that his brain was not giving him any information about the nature of the odors. He could not name odors correctly or tell them apart: he could not say whether two odors presented consecutively were the same or different, and was unable to match a sample odor to one of two choices. Interestingly, he could assign names to odors, but the ones he chose bore no obvious relation to the actual odor, and he did not use them consistently. So when he smelled a bottle containing the odor of cloves, he responded, “fresh woodwork” on one occasion and “dead fish washed ashore” the next time. I have no idea what inspired these responses.8

  To rule out the possibility that his deficit could be reduced to a general problem with naming, we showed that he could name foods when he handled them in a bag, using his sense of touch, or saw them briefly, using vision. One incident in particular captured the essence of Henry’s lack of olfactory sense: he correctly identified a lemon by sight, then sniffed it and said, “Funny, it doesn’t smell like a lemon.”9

  But Henry’s operation did not completely eliminate his sense of smell. In addition to being able to detect the presence of an odor compared to distilled water, he also performed normally on an intensity discrimination task. This task measured his ability to distinguish between different strengths of a particular odor. The examiner asked Henry to sniff one sample, then another, and to choose the stronger of two. He correctly chose the sample with the higher concentration of the odor; he just had no idea what that odor was.10

  The results of this single concerted study of Henry’s olfactory perception propelled the science forward. The revelation for neuroscientists was that the brain circuit that is responsible for odor detection—this bottle contains an odor—and odor intensity discrimination—this odor is stronger—is separate from the circuit that supports odor discrimination—this smells like cloves. Henry’s capacity to detect even weak odors, to differentiate odor samples based on their strength, and to adapt to a strong odor indicated that the machinery that carried olfactory information from the nose to the cortex was at least partially intact. In addition, it is possible that a pathway to other olfactory cortices in his frontal lobes above his eyes was spared, helping to support the preserved behaviors. Nevertheless, these remaining inputs were insufficient to maintain odor discrimination, demonstrating that medial temporal-lobe structures play a critical role in odor matching and identification. Thanks to Henry, we now know that odor discrimination takes place in the front part of the parahippocampal gyrus, the amygdala, and the cortex around the amygdala. This ability to discriminate one odor from another and to recognize specific odors depended on these areas removed from Henry’s brain, whereas the more elementary processes of detection, adaptation, and intensity discrimination relied on separate networks that were undisturbed.11

  Amnesic patients do not typically lose their sense of smell, and indeed the deficit in Henry’s case was not part of his amnesia. His loss was due to the removal of brain tissue during his operation. The continuing postmortem examination of his brain will tell us definitively about the integrity of remaining olfactory circuits, about which we could only speculate during his life. Specifically, it will help us understand the structure and organization of pathways that progressed from his nose to cortical olfactory areas in his frontal and temporal lobes.

  Knowing that Henry’s perceptual abilities were normal, save for smell, we could confidently attribute his inability to remember information received through vision, hearing, and touch to a memory impairment, and not a failure to sense the test materials in the same way as healthy participants.

  Once we ruled out sensory loss as an explanation for Henry’s deficient memory for information received through vision, hearing, and touch, we could start to catalog the deficits related to his brain operation. We were beginning to understand the extent to which memory depended on a few centimeters of tissue in the medial temporal lobe—those that Henry lacked. Today, the role of the hippocampus in memory is well established, and for decades, Henry played a key role in advancing this knowledge. At the time, however, he was our guide in exploring uncharted territory.

  The tragic outcome of Henry’s operation inspired neuroscientists to create animal models of amnesia. Initial attempts in the 1960s and early 1970s to create a memory impairment like Henry’s in monkeys and rats were unsuccessful. Animals with lesions in both hippocampi had little if any difficulty on standard memory tests. Researchers began to make progress during the late 1970s when they devised new and more challenging ways to test memory, requiring the animals to recognize complex visual stimuli or learn mazes. After scientists began recording the activity of single cells in the hippocampus, a popular theory proposed in 1978 held that the hippocampus played a key role in spatial memory, and that this neural activity resulted in the establishment of cognitive maps, mental maps of one’s environment.12

  Aware of this emerging evidence, Milner and I decided to test Henry’s maze learning ability in 1962 when I was a graduate student in her lab. We wanted to examine Henry’s memory with tasks that did not rely heavily on verbal stimuli, such as words and stories, because previous studies with Henry had already covered that ground. Pursuing this new direction, Milner and I explored his spatial-learning ability using two maze-learning problems, one executed with the use of vision and the other with the use of touch. First, Milner trained Henry on the visual maze for three days, and then I trained him on the tactual maze for four days (see Fig. 5a).

  The visual maze, placed on a table, was a thirteen-inch square wooden board with a ten-by-ten array of bolt heads set one inch apart. Milner designated a path from the start in the lower-left corner to the finish in the upper-right corner. Henry had to discover this path by trial and error. He held a metal stylus in his right hand and proceeded, one step at a time, from bolt head to bolt head. If he took a wrong step, he heard a loud click from an error counter and had to go back to the previous bolt head. Eventually he reached the finish, completing the first training trial. On the first day of training, Henry completed seventy-five trials and did the same on each of the next two days, for a total of two hundred twenty-five trials. At the end of each trial, Milner recorded the number of errors and the completion time (see Fig. 5b).13

  The tactual maze was 12.75 inches by 10 inches and had paths cut into an aluminum sheet that rested inside a wooden frame. Henry sat on one side, where a black cloth curtain covered the frame to prevent him from seeing the maze. I sat on the opposite side, which was open so I could observe his hand, the stylus, and the maze as Henry advanced through it. I introduced him to the task by asking him to put both hands under the curtain to feel the perimeter of the maze, and oriented him to the maze by guiding his right hand, holding a stylus, to the start, next to the finish, and then back to the start. I then instructed him to move the stylus along the paths to find the correct route from start to finish. Each time Henry entered a blind alley, I rang a bell signaling that he should back up and try another path. Henry completed two sessions of ten trials each on four consecutive days, and I noted his errors and completion time, trial by trial.14

  In these 1962 experiments at the Neuro, Henry failed on the visual maze and the tactual maze to reach the criterion of learning—three consecutive errorless runs. Even after completing many more trials than our control subjects needed to learn the correct route, he showed no improvement. Taken together, these experiments demonstrated that the deficit in maze learning was not restricted to a single sensory mode because it was evident when the task was done with visual guidance and also when visual guidance was completely excluded.

  In 1953, when Henry returned home from the hospital after his radical operation, it became clear to his parents that even mundane activities would be a challenge for him. His boss at Royal Typewriter in Hartford must have liked Henry and been satisfied with his work before the operation because he allowed Henry to resu
me his assembly-line job afterward. But soon the boss phoned Mrs. Molaison and told her that Henry was too forgetful to do his job. He still had a sense of what his work entailed, but lacked the specific declarative knowledge to carry out his assignment—even though it was the same task performed over and over. Now unemployed, Henry stayed home with his parents, under his mother’s constant care. Singlehandedly, she looked after all of his needs for the next three decades. Henry defined her life.

  Henry helped his parents with household chores but forgot the locations of items he used frequently. His mother had to remind him where to find the lawnmower even if he had used it the day before. He could not do anything away from the house by himself, including going for a short walk. He would read the same magazines repeatedly, and would complete jigsaw puzzles without realizing he had already done them.

  Ten months after the operation, Henry’s family moved to a different house in East Hartford, just a few blocks away on the same street. The change was drastic for Henry. He could not learn his new address and would could not guide a driver to his house. His spatial memory—declarative memory for spatial locations—was deficient.

  Four years later, in 1958, the family purchased an eight-hundred-and-sixty-square-foot bungalow at 63 Crescent Drive in East Hartford. By all expectations, Henry should have failed to remember this address too. Instead, he greatly surprised us. During a 1966 visit to MIT, Henry knew this address and was able to draw an accurate floor plan of the house from memory. Even more astonishing, in 1977, three years after he moved out of that house, he still responded with “63 Crescent Drive” when I asked where he lived, and again drew a floor plan, sketched in hesitant lines but with doors marked and rooms labeled. I contacted the person who then lived at 63 Crescent Drive and obtained the floor plan. The layout matched Henry’s drawing, and he was able to recite this one address throughout the rest of his life.15