Permanent Present Tense

by Suzanne Corkin

  2b. The hippocampus and entorhinal and perirhinal cortices

  A different view of the same brain, as if we are face to face with the person. The gray matter follows the cortical ribbon along the entire cerebral cortex, while the white matter lies beneath the gray matter. The hippocampus and entorhinal and perirhinal cortices reside in the medial temporal lobe seen in the lower right of the image. The hippocampus is outlined with a solid white line, the entorhinal cortex is shown with horizontal hatched lines, and the perirhinal cortex is shown with vertical hatched lines. Henry’s operation removed all three structures on both sides of his brain.

  3. Henry’s MRI

  These MRI images collected in 1992 show Henry’s lesions on the left and right sides of his brain. The asterisk indicates the missing portion of the medial temporal lobe structures. The remaining portion of the hippocampal formation is indicated with an open arrow. We can see approximately two centimeters (.79 in.) of remaining hippocampal formation on each side. The enlarged spaces between the leaves of the cerebellum are evidence of substantial cerebellar degeneration.

  4. Mooney Face-perception Test

  An item from the Mooney Face-perception Test. When Henry was forty, we asked him to state the sex and approximate age of each person depicted in the test stimuli. He scored higher than the control participants, indicating that his visual perception was intact.

  5a. Visual stepping-stone maze

  The visual stepping-stone maze consists of black dots, which are metal bolt heads on a wooden base. Henry’s task was to discover and remember the correct route (indicated by the black line). As he proceeded from bolt head to bolt head, the click of an error counter signaled each mistake. During three days of training when Henry completed two hundred fifteen trials, he did not succeed in reducing his number of errors, revealing a deficit in his declarative memory.

  5b. Tactual stylus maze

  The tactual stylus maze rested inside a wooden frame. Henry sat on one side, where a black 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 instructed him to move the stylus along the paths to find the correct route from the start to the finish, and each time he entered a blind alley, I rang a bell signaling that he should back up and try another path. On four consecutive days, Henry completed two sessions of ten trials each but without decreasing his error scores, indicating a failure of his declarative memory.

  6. Route-finding task

  One of fifteen large maps used to test Henry’s spatial ability. The map depicted the nine red circles on the floor of the testing room. A path from dot to dot was drawn in heavy black lines, with a circle around the starting point and an arrowhead at the end. An N, designating north, was marked on each map, and a large red N was fixed on a wall of the room. Henry’s task was to walk from dot to dot along the path that corresponded to the one on the map. He walked patiently from dot to dot, but was usually unable to follow the path indicated on the map, and his performance did not improve with repeated testing using the same maps. Here, the dotted line shows where he went off course.

  7. Limbic system

  Although the idea that a single brain system supports emotion is no longer tenable, the term limbic system is still used to designate a group of interconnected structures that play a role in the appreciation and expression of emotion: the hypothalamus, thalamus, amygdala, cingulate cortex, and orbital frontal cortex. The orbital frontal cortex is the area above the eye, and the cingulate cortex is the gyrus just above the corpus callosum. Because the amygdala and hippocampus are heavily interconnected, our emotions can influence memory formation, but the hippocampus itself does not modulate emotions.

  8. The typical neuron

  Our brains contain billions of neurons that are constantly talking to each other. The typical neuron has several parts. Each neuron has a dendritic tree that receives thousands of signals from other neurons. This information is processed in the cell body and from there, it travels along the axon for transfer to other neurons. The point where neurons contact each other is the synapse.

  9. Mirror tracing task

  Milner’s trailblazing discovery in 1962 showed for the first time that amnesia spares some kinds of learning. She gave Henry the mirror tracing task, which required him to trace around a star—a challenging enterprise because he could only see the star, his right hand, and the pencil in a mirror. Even so, his performance improved measurably during three days of practice. At the same time, he had no conscious knowledge of this experience or his accomplishment, suggesting that the brain houses two different kinds of long-term memory, one in which he succeeded (nondeclarative) and another in which he failed (declarative). Decades later, my lab repeated the mirror tracing experiment and showed that Henry retained the skill when we retested him almost a year after our first test session.

  10. Rotary pursuit task

  To begin the rotary pursuit task, I asked Henry to rest the tip of the stylus on the target. The disc began spinning, and for twenty seconds he tried his best to keep the stylus in contact with the target; I recorded the time that the stylus remained on the target, as well as the number of times it left. Over the seven days of testing, Henry’s scores improved, although not as much as the control participants’. Following an additional week without practice, he retained this skill.

  11. Bimanual tracking task

  Henry’s job on the bimanual tracking task was to maintain contact with the tracks as the drum rotated for twenty seconds. This task was especially difficult from a motor-control perspective because his brain had to coordinate the movements of his left and right hands and his eyes, which moved back and forth from one track to the other. Although Henry’s scores were inferior to the control participants’, and he was less consistent, he again demonstrated a clear improvement from trial to trial on this motor learning task.

  12. Coordinated tapping task

  To perform the coordinated tapping task, Henry held a stylus in his right hand and tapped the circle on the right in the order 1–2–3–4. Then, with the stylus in his left hand, he tapped the circle on the left in the order 1–2–3–4. I next asked him to tap the two targets simultaneously, which was especially demanding because he had to tap the two 1s simultaneously, the two 2s simultaneously, and so on. He had to coordinate the movements of his left and right hands, and because the location of the numbers differed between the two circles, each hand had its own trajectory to follow. On this self-paced task, Henry scored as well as the control participants, and when I retested him after a break, he was faster than he had been initially.

  13. Sequence-learning task

  For the sequence-learning task, we asked our Parkinson disease patients to sit in front of a computer terminal and view four small white dots arranged horizontally across the bottom of the screen. On each trial, a small white square appeared below one of the four dots, and the participant’s task was to press, as quickly as possible, the key that corresponded to the location of the square. Unbeknownst to the patients and controls, the squares appeared in a ten-item sequence that repeated ten times on each trial, for a total of one hundred key presses. We found that the early stage Parkinson patients and controls learned the sequence: their response times became progressively faster on trials that contained the repeated sequence but did not speed up on other trials in which the sequences were random. In contrast, the patients with Huntington disease did not show this nondeclarative learning.

  14. Reaching task

  For the reaching task, we showed Henry individual targets on the screen and asked him to use the mechanical arm to move the cursor to those locations as quickly as possible. His goal was to reach the target within one second, and each time he succeeded, the target exploded. After Henry spent a few minutes moving the cursor to the targets, we changed the procedure without warning; the mechanical arm imposed a force on his hand, throwing his movements off-course t
o one side. With practice, however, he altered his motor commands to compensate for the force, and was again able to quickly move his hand in a straight line to the targets. We knew that Henry had learned to compensate for the force because when we suddenly removed the force, his movements had large errors, just like the pattern of errors he had made early in training but reversed.

  15. Basal ganglia

  The basal ganglia are a distributed set of interconnected circuits that work in collaboration with the cortex to achieve the control of posture, movement, and unconscious learning. The key basal ganglia structures are the striatum (caudate nucleas and putamen), nucleus accumbens, globus pallidus, subthalamic nucleus, and substantia nigra. Information flows in a loop from areas in the frontal and parietal lobes through the basal ganglia and thalamus and then back to the frontal cortex.

  16. Eyeblink conditioning task

  For the eyeblink conditioning task, Henry sat in a comfortable chair and wore a headband that held an air-puff jet and a monitor to record his eyeblinks. We gave him these instructions: “Please make yourself comfortable and relax. From time to time, you will hear some tones and feel a mild puff of air in your eye. If you feel like blinking, please do so. Just let your natural reactions take over.” Over an eight-week period, Henry performed two kinds of conditioning tasks: delay conditioning and trace conditioning. Although his performance was inferior to that of the control participant, he did produce conditioned responses in both the delay and trace procedures—evidence of nondeclarative learning.

  17. Gollin Incomplete Figures Test

  The Gollin Incomplete Figures Test is a measure of perceptual learning. Henry’s task entailed viewing simple line drawings of twenty common objects and animals, such as an airplane and a duck. The test began with a very sketchy representation containing a few parts of each object, making it almost impossible to interpret, and ended with a complete, recognizable picture. Henry first saw the most fragmented set, one drawing at a time, each for about a second, and said what he thought the drawing might represent. He then saw progressively complete sets of pictures until he could name all twenty objects. He completed the test without errors after four trials, and remarkably, his accuracy was a bit better than that of the ten control participants. An hour later and without warning, Henry saw the same set of pictures again and identified the fragments in fewer trials. He had learned a perceptual skill without explicit knowledge, and it stuck—solidly stored in the preserved cortical areas of his brain.

  18. Pattern priming

  The dot patterns for pattern priming are in column one. Examples of the target figures that Henry copied are in column two. Some other figures that could be drawn are shown in the remaining columns. After Henry copied a target figure onto a dot pattern, he was later likely to draw that figure onto a dot pattern when asked to draw whatever he wanted. On three different forms of the pattern-priming test administered on three separate testing occasions, Henry showed a normal magnitude of priming, attesting to his intact nondeclarative memory.

  19a. William Beecher Scoville

  19b. Brenda Milner, circa 1957

  20. Five-year-old Henry and his parents

  21. Henry the animal lover

  22. Henry before his operation

  23. Henry, 1958

  24. Henry with his parents after his operation

  25. Henry, 1975

  26. Henry ready for testing at MIT, 1986

  27. Henry at Bickford Health Care Center

  28. Henry’s drawing of the floor plan of his home

  29. Henry’s spoon

  For Henry, the target explosion triggered childhood memories of going hunting for small game. As he performed the task and earned numerous explosions, he described these cherished memories in detail—the type of gun he used, the porch in the rear of his childhood home, the terrain of the woods in his backyard, and the kinds of birds he hunted. Smiling and excited, he repeated these facts many times during the two-day experiment. It was an emotionally upbeat experience for him.29

  After Henry spent a few minutes moving the cursor to the targets, we changed the procedure without warning; the mechanical arm imposed a force on his hand, throwing his movements off-course to one side. So, instead of moving to the target in a straight line, his hand swerved on the way to the target. With practice, however, he altered his motor commands to compensate for the force, and was again able to quickly move his hand in a straight line to the targets, consistently achieving the timing goal of 1.2 seconds or less. His brain constructed an internal model of the skill that allowed him to estimate the force in the mechanical arm and counterbalance its effects. That he learned to compensate for the force was evident: when the researchers suddenly removed the force, his movements had large errors, just like the pattern of errors he had made early in training but reversed. At the end of the session, the researchers politely thanked Henry for his time, and he left to have lunch.30

  Four hours later, when Henry returned to the testing room, he had forgotten entirely about the apparatus and the experiment. The researchers pushed the mechanical arm aside and asked Henry to sit down. He sat down, and then something interesting and unexpected happened. In contrast to the first time he encountered the equipment, this time he voluntarily reached out and grabbed the handle, brought it toward him, and looked at the video monitor in anticipation of seeing a target. Clearly, despite having no conscious recollection of having performed the task before, some part of Henry’s brain understood that the contraption was a tool that enabled him to move a cursor on the monitor. When a target was presented, he showed strong aftereffects of the previous training. Because his brain expected the mechanical arm to perturb his movements as it had before, it generated motor commands to compensate for these forces, and he moved the handle to the target as if the force were still in place. The motor memory was much more than knowing how to manipulate a tool; it included information about the rewarding nature of the tool’s purpose. In essence, “when I move the handle quickly, something fun will happen.” The sight and touch of the mechanical arm were sufficient to encourage a motor act that Henry expected to be rewarding. If in the first session, use of the mechanical arm had been paired with a shock or another noxious stimulus, then Henry likely would have been reluctant to use the device again.31

  Henry’s performance on the reaching task demonstrated that his brain had gained three important insights, all without conscious awareness and without the use of his medial temporal lobes. First, during the initial training session, he learned to use a novel tool to achieve a specified goal, both without and with the disrupting force. Second, when tested hours later, the sight of the tool was sufficient to produce voluntary use, suggesting that Henry had learned and stored the potential rewards associated with the use of the tool—the challenge of earning the explosion. Third, seeing and holding the tool were sufficient to allow him to unconciously recall both the purpose of the tool and the motor commands needed to achieve that purpose—even though the same visual and tactual information were insufficient to evoke a conscious memory that he had previously trained on the task.32

  Unlike the earlier motor-learning experiments using rotary pursuit, bimanual tracking, and tapping, the mechanical-arm experiment allowed us to examine two properties of motor control separately: kinematics and dynamics. Kinematics refers to the speed of motion, changes in speed, and direction of motion, while dynamics refers to the effect of forces on motion. Although Henry experienced considerable difficulty learning the kinematics of the task, he finally learned that he had to move the arm away from himself to make the cursor go up on the screen and toward himself to make it go down. He was also able to compensate for the imposed force (the dynamics) and move his hand in a straight line to the targets. The goal of our experiment was to see whether Henry’s impaired declarative memory would have any effect on the acquisition of these complex motor memories; remarkably, it did not. Just like the control participants, his brain could build new internal models to su
pport the learning of this motor skill.

  Milner’s trailblazing discovery in 1962 that Henry could learn a new motor skill was a tremendous advance, providing a new way to understand how we acquire and retain nondeclarative memories. Since then, researchers have devised thousands of experiments to shed light on the cognitive and neural processes that support this kind of memory. Currently, experiments focus on the cellular and molecular mechanisms of neuroplasticity in the brain circuits that underlie skill learning. Accrued knowledge from these findings may point the way toward treatments for such diseases as Huntington and Parkinson.

  Because movement is a fundamental requirement for interacting with the world, the performance of motor skills is critical to our independence. One mystery of motor skills is how we are able to execute them so quickly and with so little thought. When we are first learning a new skill, we need to put a lot of concentration and effort into it in the form of executive control. Over time, skills that we acquire become increasingly automatic; they require much less mental exertion. Researchers have studied how new motor skills become automatic, and through the use of brain-imaging techniques, we can see how brain activity changes as people master skills.