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don’t know if he had an extra large—or in any other way different—hippocampus. Meanwhile, Henry Molaison is still, even after his death, contributing to science. In his will, he bequeathed his brain to research, and the researcher who worked most closely with him for the last forty years of his life, neuroscientist Suzanne Corkin, planned to give her subject an afterlife in her field. After Henry’s death on December 2, 2008, Corkin worked together with a large team of physicians and researchers to make his brain work for posterity. First, researchers at Harvard scanned the brain with a magnetic resonance imaging (MRI) machine in Boston. Then, Corkin placed Henry’s brain in a cooler and handed it over to brain researcher Jacopo Annese, who took it on a plane bound for San Diego. Annese’s Brain Observatory stores the donated brains of deceased people so they can be used in various avenues of research, including on Alzheimer’s and normal aging. There, Annese’s team was ready and waiting to cut Henry’s brain into slices, thin as strands of hair. “We believe that the enormous attention that was devoted to patient H.M. when he was living and generously served as a keen research subject ought to be matched by a similarly involved study of his brain,” Jacopo Annese said.
Henry’s brain needed special attention. No other brain at the Brain Observatory had received as much scientific attention as his. The team photographed every single one of the 2,401 slices of Henry’s brain and stored them both in formaldehyde and as digital files. They spent fifty-three hours doing so, and Annese didn’t sleep until he was sure that all the pieces of this exceptional brain were securely preserved. Thanks to his work, researchers can now study the exact location where Scoville made his mistake and speculate about which of the remaining areas, near the hippocampus, helped Henry remember the few things which he occasionally and surprisingly did remember. In May 2016, Corkin passed away at age seventy-nine, and her brain is now in the safekeeping of other brain researchers. It contains no unusual surgical scars but houses decades of memories of her special contributions to research.
Henry Molaison’s legacy was an entirely new field of research. Now the hippocampus has a definite place in our memory. And during the past fifty years, memory research has become more and more focused on mapping memories all the way down to the cellular level.
“I believe that we will achieve the goal of explaining memory in the brain within my lifetime,” says one of the leading memory researchers in the world, Eleanor Maguire, professor at University College London and Wellcome Trust Centre for Neuroimaging. Her research, which focuses on the hippocampus, has allowed her to “see” memories. In one experiment, she told test subjects to think of a certain memory while she watched, through an MRI machine, the patterns that lit up their hippocampus. When they thought of other specific memories, different patterns became visible.
“Your experiences are taken into the brain. After that, the experience is taken apart and stored away in little pieces in the brain’s neocortex. Every time you recollect it, it is brought back to life. The hippocampus is critical to reconstructing the memory in your mind’s eye, enabling you to relive it once more,” says Maguire.
Memory research is also, in a sense, a process whereby small pieces are assembled into a larger puzzle. Memories cannot be seen, per se. No one can retrieve a memory and put it under the microscope. That’s also why it took so long for memory to move from being strictly a philosophical and literary topic to being the object of scientific examination. Psychology is a relatively new academic discipline, and so the scientific study of memory has a shorter history than that of many other subjects. But when memory researchers started piecing together human memory, they gave us a picture of an amazing inner world. They worked tirelessly with lists of words, meaningless shapes, staged bank robberies, life stories, puppet shows, and strings of numbers, all to reveal the truth about memory by using the brains of the people who volunteered to be guinea pigs.
Some of you will probably argue that it’s meaningless to measure something so abstract, a thing that exists only for the individual who owns the memory. How will we be able to reduce the evocative descriptions of memories in Marcel Proust’s seven volumes of In Search of Lost Time into figures and scientific graphs?
To capture unique human experiences and turn them into science, isn’t that a paradox? Like putting a seahorse in a glass of formaldehyde hoping to preserve its beauty and essence forever?
There are, however, many good arguments for why memory research is necessary. Turning memory into something concrete and measurable helps us compare memory in the healthy and in those with diseases, and it can help people with memory problems. It contributes to our understanding of how the brain works, which in turn may help find the solution to major medical issues of our time, such as Alzheimer’s, epilepsy, and depression.
Some 140 years of measuring memory has not solved all its riddles—far from it. Disagreements come and go on the memory battleground. One longstanding dispute is referred to as the “memory wars.” One side maintains that, in extreme situations, memory will behave differently, producing things like repression and dissociation. The other side maintains that memory always behaves the same way, only much more strongly in extreme situations. Another hot issue is the possibility of memory training: Is it like strengthening a muscle—that is, it gets better with repetition—or can you use strategies and techniques to improve existing ability? And what exactly is memory? Even this is being debated in minute, technical detail in scientific papers—debates punctuated by indignant letters to the editors of scientific journals—while researchers try to gain ground in the scientific community. It’s almost like an election campaign in slow motion, or a TV debate spread out over fifty or a hundred years.
There’s even discord over the hippocampus. Two camps face each other. One rigidly believes that the role of the hippocampus is simply to consolidate memories into the rest of the brain. As time passes—sometimes with the help of a good night’s sleep—memories attach themselves to more robust cortical networks, while the seahorse slowly and carefully lets go of the memories it has been tending. The other camp argues that this is too simple. This group adamantly insists that the seahorse holds on to memories, especially the personal, vivid sort that we remember in something resembling a personal memory theater, at the same time as they are also stored deeper in the cortex. Every time we recall a memory, they say, the hippocampus is involved and “overwrites” the original memory, each time with a slightly new interpretation or reconstruction.
In the same way as the seahorse’s ocean ecosystem is important to understanding its existence, the hippocampus’s brain ecosystem is important to understanding how memory is kept and recalled. In the past few years, people have been paying more attention to how the hippocampus interacts with the rest of the brain. Memories play out in physical networks, where different parts of the brain move as in a synchronized dance. It’s visible with modern MRI methods. William James, one of the fathers of psychology, understood it already in 1890:
“What memory goes with is, on the contrary, a very complex representation, that of the fact to be recalled plus its associates, the whole forming one object, … known in one integral pulse of consciousness … and demanding probably a vastly more intricate brain-process than that on which any simple sensorial image depends.”
In other words, each memory consists of different bits and pieces brought together in one unified wave of consciousness. Each part of the memory originates in a different part of the brain, where it first made a sensory impact. To make the whole thing feel like one experience, one unique memory, requires intricate brain interaction. William James didn’t know exactly how this worked, but thinking of memory and mind the way he did in the 1890s was remarkable. When James was alive, people thought of each memory as a unit, a copy of reality, like something that could be pulled out of a folder in a filing cabinet. That the key to understanding memory was the seahorse—slowly swaying in rhythm with the sensory areas and the emotion and awareness centers of the brain—wouldn’t be discovered for another hundred years. Just a few years before James’s armchair observations, researchers had discovered how neurons are connected to each other with a slight gap in between them called a synapse: the so-called neuron doctrine. From that discovery to today’s brain research, where we can virtually watch memories come to life in the brain, has been a long journey.
We can all benefit from making that journey and learning more about