The memory alchemists turning rain to gold

You cover such broad ground in Adventures in Memory, pairing findings from neuroscience research with insights from literature, psychology, history, anthropology, architecture, mythology, and more. Why did you choose to incorporate so many different perspectives?
Memory is so much more than the physiological processes within and between neurons in the brain. It concerns all of us, and makes an impact on – and is impacted by – all aspects of culture and society. We wanted to show through vivid examples why memory matters. We were also fascinated by the collective memory of human civilisation – the history books and literature that allow us to learn from our shared past. We felt that had to be reflected in the book as well.

In Adventures in Memory, you also interview some fascinating characters, including people with extraordinary memories as well as those with extraordinary problems remembering. What were some of the highlights from these conversations for you
Our conversation with Adrian Pracon, one of the survivors of the terrorist attack and mass shooting in Utøya, Norway, made a lasting impression on us. It is difficult to remain unmoved by his account of how the traumatic memories have tormented him. He took us on a trip to the Island where he and so many teenagers and young people were shot down. That experience, walking through the beautiful spring scenery while he showed us where he hid and where he saw people being killed… it was such a strong contrast. How can you live with memories like that and integrate them into your life, without being crushed by them?

We also talked to several people who had lost memories of their childhood and youth, in part or completely, and we were fascinated by how they coped with what we would consider terrible circumstances. It is really possible to live a happy life without all of your memories? In a way, their story is true for all of us – we forget far more than we remember. We just never think of all the stuff we have forgotten!

What is a 'cumulative' memory? Is this different from what you call a 'false memory'?
A false memory is by definition something that has never happened, which you remember as if it were real. Cumulative memory, on the other hand, is a term we use to describe memories of events that have been repeated many times, like taking the bus to work or cuddling your child at bed-time. Because we don't remember each separate instance the event took place, we construct a compilation of all those instances, so to speak. These compilations are similar to false memories in that they are not necessarily true renderings of the past, just approximations. All those times you took the bus were unique, and likely none of those experiences were exactly like what you imagine when you think about 'taking the bus'. But really all memories, true or false, are constructed in our minds. There isn't as much of a difference between 'true' memories and false memories as we like to think.

Many of the people you interview in Adventures in Memory have gone to outrageous lengths to improve their memory. We meet taxi drivers who had to train for years to navigate London's crooked streets; quiz masters who diligently read their morning newspaper with a notepad and pen at their side; and a World Memory Champion who uses decks of cards to memorise lists of completely useless things. What drives us to these extremes? Why is remembering so important to us?
Remembering gives us a sense of being in control and on top of things, whether it is control of performance and achievement, of our personal history, or of time itself. But for most of us, this is an illusion. Even if some of our experiences are etched into our brains as memory traces, they always come back to us transformed – perhaps even better than before, as Marcel Proust, author of In Search of Lost Time, might argue. It's funny: we fear the loss of control that comes with forgetting, but most of us don't even know what it is that we can no longer remember.

There's a very provocative line in the book: 'Forgetfulness is underrated'. Can you expand on this idea?
Remembering and forgetting are both integral parts of memory. Forgetting is our brains' way of tidying up so that the memories that remain can stand out and shine. Forgetfulness is nature's way of showing us that time that has passed is best reconstructed, often with flaws, rather than remembered in perfect detail. And think about it: isn't it a relief to forget sometimes? Good riddance to all those mundane seconds of our lives and all those bad feelings! And when it comes to the good experiences, forgetting what it was like to ride that roller coaster the first time around makes the experience all the more exhilarating on your next visit – if roller coasters are a good thing, that is.

What was it like to write this book together as sisters?
It was both a lot of fun and a challenge. We contributed equal amounts to the book, through writing, experimenting, and generating ideas. Going places and interviewing people together was really great, as was setting up experiments. As sisters, we are more honest with each other than most people, which actually helps with the writing process. Let's just say that this adventure has given us a whole bunch of new memories together.

Ylva, you're a trained neuroscientist. Did you learn anything new while working on Adventures in Memory?
Definitely! There are so many winding roads of memory research that I wouldn't normally go down in my day-to-day work. And as a clinician, I mostly see clients with memory complaints, so learning more about people with superior memory abilities was an eye-opener. Also, learning from Hilde that memory was considered a divine art by 16th and 17th century alchemists was really fascinating. Writing this book has truly been inspiring for my research.

Hilde, you have some thought-provoking ideas about the connection between memory and writing, drawn from your own experience as a journalist and novelist. Can you tell us more about it?
While writing this book, it dawned on me how closely related the art of storytelling and the act of remembering are – how our stories and all of the most beautiful pieces of literature are structured just like memory itself. So learning more about memory definitely taught me more about writing.

Also, as a historian, I realised how much focusing on our individual, fallible memories can be a mistake, especially in a court of law. False memory research started in the 1970's because researcher Elizabeth Loftus wanted to examine why we so often wrongly accuse people of crimes they never committed – and do so with so much certainty. In truth, our memories are very unreliable, and she proved that through a number of spectacular experiments, including tricking people to think that they loved asparagus or hated eggs. I believe memories are supposed to be collective; together we can remember more than we can alone. Our stories, together, connect us to each other, keeping us within a shared reality.

Lately, there's been a lot of emphasis on mindfulness, on learning to live in the present moment rather than letting the mind wander. But in the book, you write that 'mindfulness has given future thinking a bad name'. Can you explain what you mean?
Mindfulness is actually not about living in the present; that is a common misunderstanding. Instead, it involves a controlled form of mind wandering, in which one anchors the experience in the present moment. So it's actually more correct to say that the misunderstandings around mindfulness and the hype it has created has given future thinking a bad name. People mistake mind wandering with rumination and loss of control. But rumination is not the same as mind wandering; it's really a form of stagnated thinking. In life, we need these free moments of mind wandering to let our mental time machine run, process our memories, and develop a vision for our future. 

You talk to many of the main players in terms of psychologists studying memory. Did you find anything notable about them as a group?
One thing that strikes us is how versatile these scientists are. Alan Baddeley may be known for his working memory model, but he has done so much more – the diving experiment, a system for making the postal codes in UK more memorable, to mention a few – and the same goes for Eleanore Maguire and Edward and May-Britt Moser. While they have their specialized fields of memory research, they are constantly developing new ideas. And they were all great fun to talk with! They are such an inspiration.

At the same time, we must not forget that many researchers are contributing to the field through rigorous work that may not seem groundbreaking or spectacular. But without it, science would not go forward. The interdisciplinary nature of memory research also means that no one researcher or research group can grasp the whole understanding of what memory is. It is such a beautiful example of how the scientific community works as a whole to push knowledge forward.

Ylva, I loved the phrase – actually your sister's, but about what you were doing – 'As if you were a memory alchemist and transformed the day into gold!' Tell me a bit about your approach to remembering at that stage of the book, and whether you have kept it up.

I wanted to know whether it was possible to keep more of my everyday life in my memory, but in the end, it turned out to be an exploration of the bliss of forgetting. In order to remember each day, I inserted an avatar representing the day of the month into the events of that day. So for the 7th, it was gold (because to me personally, the number seven is golden – a slight case of synesthesia of mine), so gold nuggets would lie around in the wet snow on the pier when we watched the divers in February, and the rain turned into tiny bits of gold falling from the sky outside the coffee shop were we used to sit while writing the book.

The experiment made me really thankful for the memories I do get to keep, and perhaps more aware of the fact that the moment in the here-and-now may not be re-experienced, and that I simply do not have control over that. Also, the task turned into an obsession while it lasted, even to the extent that my mindset wouldn't let go immediately after the 100 days were over. When it finally did, and I turned back to normal, it made me more content with what I forget. At the same time, those golden moments also remind me of the parts of my life that don't stand out as particularly noteworthy and spectacular, just those everyday moments that is life, and I still wish I could remember more of them, too. It is a dilemma. Now, almost three years later, I can feel forgetting eating away at those memories, and I think a vast amount of it is now gone, despite my efforts. Trying to control memory is like trying to hold back the sea.

I have not kept it up. That would be insane. With my limited memory, trying to keep track of all the days of my life is a terrifying idea! But what I have kept, and what Hilde has taken away from it too, is the idea of cherishing the details of memories, even if they are not spectacular, and using them to heighten awareness of being alive and boosting happiness.

Final thoughts, Hilde?

Since research shows that depression is transforming our memories, making them more general and vague, I reckoned that happiness is in the details – you know they say 'the devil is in the details', but obviously that's where happiness dwells, too! So I started focusing on the beautiful, everyday details in my life, trying to cling on to them. Actually they started using this tecnique in therapy, too. Whenever I feel a little bit down I try to focus on my daughter's beatiful eyes, or the colour on the flowers in my dining table. It really helps. Also, this is the very nature of literature, the awareness to details. So reading will also make you feel better. 

- Hilde Østby is a writer and editor and the author of Encyclopedia of Love and Longing, a novel about unrequited love that was published to critical acclaim in Norway. She has a master's degree in History of Ideas from the University of Oslo.

- Ylva Østby is a clinical neuropsychologist with a PhD from the University of Oslo who devotes her research to the study of memory. She is also vice-president of the Norwegian Neuropsychological Society. She lives in Oslo, Norway.

Adventures in Memory: The Science and Secrets of Remembering and Forgetting is published by Greystone Books. 

Here we extract an exclusive chapter, with kind permission.

Chapter 2: Diving for Seahorses in February

Or: Where do the memories go?

Beyond the pier at Gylte Diving Center, an hour's drive out of Oslo, Norway, there are more than forty different types of marine slugs (nudibranchs). They come in all colors, from dark purple to transparent white. Their bodies are covered with tentacles with small stars at the tip, or are decorated with pink fringes like a Disney character from the 1950s. They stretch orange fingertips toward the shiny ceiling of the water's surface or defiantly pull their luminescent, light-green feelers into their bodies. They slither around in clouds of glittery particles that swirl around the water here by the pier.

The water is only forty degrees Fahrenheit. Farther into the fjord, we've seen ice floes bobbing up and down at the water's edge. Soon, the slugs in the water will be joined by ten black-clad men chasing the seahorse's secret. The divers' flippers thump against the pier as they hobble like penguins toward the sea, then swirl up clouds of particles as the divers slowly sink to a depth of fifty feet. From our vantage point on the pier, we can see bubbles on the dark surface of the water, revealing where the divers are. The seahorses they are looking for are not in the water – we are, after all, in the Oslo Fjord. No, they are hidden beneath their tight diving hoods. The divers have plunged into the ice-cold February water to find out what goes on in the hippocampus. They're hunting for memory.

Together we are going to find out how memories behave when they enter our minds. Researching memory is, in a way, quite similar to diving. Our divers are about to break the surface and descend into the depths of memory itself. The only sign that there are memories below the surface is what rises and bursts, like the divers' bubbles breaking the surface of the water.

The experiment we are re-creating, famous in memory research, was first conducted in 1975 off the coast of Scotland. Memory researchers Duncan Godden and Alan Baddeley decided to test a popular idea, that you can remember something better when you return to the place where it happened. You know, like in crime novels, where the detective remembers an important detail when he returns to the scene of the crime. It's a simple theory: when we are in the same environment as we were when an event took place, the memory of it will come streaming back, whether we want it to or not.

Are memories easier to recall at the location where we first encountered them? How and where do they find a permanent place in our brain? To properly test this, Godden and Baddeley constructed an experiment in which people had to perform a task in two different environments, on land and underwater. Their assignment was to memorize lists of words either on the pier or twenty feet deep in the water, and later recall the lists either on the pier or in the water. One list was to be learned on the pier and recalled on the pier. After some time, a second list was to be learned underwater and recalled on the pier; a third list was learned underwater and recalled underwater; and a fourth list of words was learned on the pier and recalled underwater. The researchers anticipated that everything going on in the water – the cold and wet environment, breathing through masks, and so on – would make the divers remember less than they would on the pier. Theoretically, it should also be harder to learn something underwater as opposed to on land, given that the pressure and the mixture of gases the divers breathe would make it more difficult to focus.

On this cold February morning in 2016, when we send our divers into the Oslo Fjord, it's the first time anyone has repeated Baddeley and Godden's experiment in seawater – some have re-created it in a swimming pool, but we all know that's not the same. Will these ten men – thirty to fifty-one years of age – show the same results as in the legendary British experiment?

"Now I can tell you exactly where I have been underwater, after many thousands of dives. I could not do that before," says hobby diver Tine Kinn Kvamme, the experiment photographer. The lack of oxygen underwater, along with the stressful experience, means that people's brains function differently from how they usually do.

"When people first start to dive, few remember anything at all, nor can they report what happened underwater. First-time divers are asked to write their names backward underwater. Often, they will write things like 'backward,' or they will turn around only one letter in their name. If you ask them how many wheels a cow has, they'll answer four," she says.

Ordinarily, memories reside within a large brain network. When memories enter our brain, they attach themselves to similar memories: ones from the same environment, or that involve the same feeling, the same music, or the same significant moment in history. Memories seldom swim around without connections, like a lonesome fish. Instead, they are caught in a fishing net full of other memories. When you want to recall a memory, you have a greater chance at catching it if you scoop up the other memories around it. When you pull in the net, it's full of memories, and you can keep hauling it in until you find the memory you're after.

Would memory still work this way in a stressful situation, with subjects who had to deal with diving equipment and other distractions? Would context help the divers remember what they learned underwater when they're also asked to remember it underwater?

The experiment in 1975 showed the expected results: the word lists memorized underwater were also better remembered underwater, and the lists memorized on land were better remembered in a dry environment. We anticipate the same from our divers, but we don't want their expectations to influence the results, so we haven't told them what happened in the original experiment.

The atmosphere is tense at Gylte Diving Center. We are not re-creating this classic psychological experiment just for fun: results from psychological experiments are not always reliable. A great deal can happen by coincidence, and it's often only the results that confirm the hypothesis that are reported, while those researchers who find opposite results tuck them away in a drawer, ashamed and disappointed. When a team of researchers took on the task of re-creating one hundred experiments from different areas of psychology, only thirty-six were successful. The diving experiment was not among the hundred re-creations – but it's having its time today, an ice-cold and rainy February day in Drøbak.

Throughout history, philosophers and authors have asked themselves what memory is, how we learn and remember things, and what makes a memory reappear. At risk of offending an entire professional group: in many ways, we can call the philosophers of ancient times neuropsychologists, because they observed and tried to understand how the brain works without having access to today's research methods. The million-dollar question that everyone is trying to answer is where in our brains our memories actually end up, and how it is possible for all our experiences to consolidate into a pink mass of brain cells and blood vessels. In 350 BCE, in De Memoria et Reminiscentia (On Memory and Reminiscence), Aristotle compared the memory process to making an impression in a wax seal. But exactly how the experiences turned into memories, he couldn't say.

By studying the divers at Gylte, we may not be able to see their brains etching words into wax seals, but we can observe how memories connect and become dependent on each other. Context-dependent memory tells us something very basic about how memories are stored. How much you know in a broad sense determines what you understand of the new things you learn. Your understanding of your new experiences depends on your prior experiences. This network of knowledge creates context for the new learnings – they get caught in the fishing net, if you will. When you know what the French Revolution was all about, it's easier to understand the Russian Revolution, and when you have gained insight into Russian Communism, it shines a new light on the French republics, and so on. When our divers eventually resurface – ice-cold faces and eager eyes – and hand us their notebooks, filled with all they remember from a list of twenty-five short nonsense words, we will see with our own eyes how their brains have worked, linking words and seaweed and cold water together into the same network. But we're still standing on the pier, while the February cold eats its way into our woolen underwear. It's anything but magical.

By contrast, during the Renaissance, in the 1500s and 1600s, many viewed memory as something magical. At the time, magicians and alchemists not only tried to make gold, but first and foremost used rituals and symbols to gain power over the world through enlightenment. Secret organizations, like the Rosicrucian Order and the Freemasons, believed that an individual could progress through many stages of enlightenment to become almighty, almost like a god. The most magical art of all was remembering, which they believed was connected to imagination, to the divine creativity of humans.

When you think about it, it's not such a strange idea, because there really is something magical about our ability to store the past and retrieve it as lifelike images. Between our temples, most of us are equipped with our own private memory theater, which continually stages performances, always with slightly new interpretations – and now and then, with different actors. Today we know that everything we think and feel takes place in our brain cells, yet it is still almost impossible to grasp that our whole lives are to be found in our brains. So many emotions – fantastic, sad, beautiful, loving, and scary experiences – are hidden in our cerebral convolutions as electrical impulses, inaccessible to other people around us. Even people who have experienced the same thing have completely different memories of it.

But what sort of physical trace does a memory actually leave in our brain, and if we can locate it, can it explain memory? Memories are both abstract (states or episodes we can return to in our minds), and concrete (strengthened connections between neurons). Memories are incredibly complex. They are more than the trivia required to win a quiz show, more than the individual facts you look for among thousands of less relevant items in long-term memory. Just think of something you have experienced, recall your memory of it, and feel the sensations it contains. Are you watching it on your inner film screen? Do you hear the sounds, the voices; do you see the smiles, the eyes of the one you're talking to? Are you on the beach on a summer's day while the waves break against the sand? And the smells! Unlike at the movie theater, here we can smell the cinnamon buns and the ocean breeze, the seaweed in the bay, and hot dogs on the barbecue on the neighboring beach. You can even feel things, like the water hitting your body as you dive into the sea. All these sensations flutter about our brains as we remember. It's not possible to describe a memory by pointing to a few connections in the brain. It has to be felt.

At any rate, the hunt for the memory trace, the physical imprint of memory, has been a major part of brain research ever since neurons were discovered – well, actually, ever since Aristotle talked about wax seals. Some called it the engram, an inscription in the brain, and finding it became the holy grail of memory research. If we could find the engram, we would also understand the brain itself. With the help of our divers, we are trying to find the fishing net that holds our memories, the memory network. Every one of the squares in the net must be attached in some way; they are links that exist physically in the brain. Finding these links, and what they consist of, was a necessary step toward understanding how the brain handles memory. Before the 1960s, no one had succeeded in doing this.

A happy rabbit was perhaps all that was missing: Terje Lømo would find the very first memory trace, the smallest part of a memory, inside a rabbit brain. He is now professor emeritus in medicine at the University of Oslo and has worked mainly in physiology, the study of how the body works.

"I am most interested in how things work. Simply describing the brain was not enough for me," he says.

In 1966, he was leaning over a rabbit. It had once lived in the countryside, happily eating clover, without a care in the world. In the hands of Lømo, though, it now faced a problem. There it lay, sedated and with a fairly big hole in its brain, while the researcher came closer with tiny electrodes.

"We sedated the rabbits and sucked out a little of their cortex, so that the hippocampus was exposed. Then we poured warm, clear paraffin in the hole; it gives a good view, keeps everything in its place, and makes it warm and moist enough for the brain to continue working through the experiment. We had a window into the hippocampus."

His main goal was to find out what happened when he sent small electrical impulses through the brain, not because he was particularly interested in the hippocampus, but because that part of the brain was easier to observe. As opposed to the very complex cortex, the layout of the hippocampus was much simpler and more understandable, and the routes through it were already well known.

At the time, Lømo worked with Per Andersen, who had discovered that neurons could suddenly send off a train of signals, which were first measured by small electrodes used in experiments originally not concerned with memory at all. But neither Andersen nor other researchers knew what these signals meant. Now Lømo had decided to examine them more closely, which is where the happy – but soon dead – rabbit came into the picture. Lømo used a small electrode to set off tiny electrical impulses to travel from one part of the brain into the rabbit's hippocampus, where he measured the signals with a small receiver.

What young Lømo found was astounding and had never before been described. When he sent these electrical impulses through the rabbit's hippocampus in small "trains" of repeated signals, the cells at the other end eventually needed less stimulation to become triggered.

Some form of learning must have taken place; it was as if the neuron remembered that it was supposed to send its impulse when it had received the message from the preceding neuron! As if, initially, the first neuron had to nag it to send its signal: "Come on, come on, come on, fire already!" After having been prompted enough times, it understood to fire after just a cautious "Fire now!" And this response persisted. Something had permanently changed in the brain.

What he'd discovered was simply the smallest part of a memory, a tiny little memory trace. This response is now called long-term potentiation, meaning that a physical change occurs in some synapses in response to a recurring stimulus. At the same time as Lømo was making his discovery, neuroscientist Tim Bliss – a few thousand miles away from Oslo, at McGill University in Canada – had been looking for memory on a cellular level. What he lacked was the evidence that strengthened synapses were connected to memories. That is, until Lømo stumbled upon long-term potentiation! Bliss traveled to Oslo and the two did some experiments in 1968 and 1969, resulting in a scientific paper they published in 1973. Their paper presented a theory of how a memory is created on a micro level.

Almost nobody paid attention to the paper until twenty years later, because academia wasn't ready for it. There was simply no context; no other studies had trodden even close to this particular corner of research. Since then, though, Bliss and Lømo's paper has formed the basis for much of modern memory research. And now we know more: a memory consists of many of the connections they documented. One neuron can participate in many different memories. Memories are large networks of connections between neurons in the brain. When something becomes a memory, new links form – neurons either turn on or turn off, and either fire or don't fire a signal in the brain, and in that way form a pattern.

Our memories cannot all remain in the hippocampus, so they spread out across the cortex. It takes time before a memory matures and all the complex connections it requires to store all that makes a memory – smells, tastes, sounds, moods, and images – are established in the brain.

"Sleep is needed for a memory to consolidate. We believe that while we're asleep, we go through the events of the day in order for them to attach to the cortex. But when we are stressed, this doesn't always happen. The neurons don't fire in the same way. When I tried to re-create my experiment on other rabbits a couple of years later, it didn't work," Lømo recounts.

He'd been lucky the first time he experimented. His rabbit, despite its untimely end, had lived a happy life. The rabbits in the second experiment were stressed, so the neurons in their brains didn't work as they should have. In other words, you must treat your test animals nicely if you want to learn from them. The same goes for humans: when we are stressed, we don't retain memories as easily as when we are happy and relaxed.

At about the same time as Lømo's discovery, there were other breakthroughs in the hunt for the memory trace. In 1971, John O'Keefe at University College London found cells in the hippocampus that remember certain locations. For example, there are some cells in the hippocampus that are active only when we sit on a certain chair, and not on another chair – even in the same room. It is evidently up to some cells (place cells) to remember where we have been at all times. But to remember a place in and of itself – is that a memory? The Norwegian neuropsychologists May-Britt Moser and Edvard Moser – together with John O'Keefe – were awarded the Nobel Prize in Physiology or Medicine in 2014 for their work on that very question. The two Norwegians received the prize because they decided to develop O'Keefe's research further and look beyond the hippocampus. Their work examined the entorhinal cortex, which connects the hippocampus and the rest of the brain. The Mosers experimented with rats, which, when they were free to explore their environment, showed cells firing in exactly that part of the brain.

With tiny metal electrodes surgically inserted into their brains, these rats wandered around their cages. A single neuron in the entorhinal cortex didn't react to just one place the rat had scurried to, like place cells, but to several places. Amazing, that what they were expecting to be place cells didn't remember only one location but several locations in the same area! But when the Mosers marked the points in the cage where the cells had fired, they formed a perfect hexagon on their computer screen. The more the rats ran around in their cages and mazes, the more obvious it became; on the Mosers' computer, a clear honeycomb pattern emerged. One cell, one hexagonal grid pattern. It was a coordinate system of the environment.

"At first, we thought there was something wrong with our equipment," Edvard Moser says. "The pattern that emerged was too perfect to come out of something real."

Each of these neurons makes its own grid, each slightly offset from that of the neighboring cells, so that all points in the environment are covered. Some grids are fine-meshed, while others react to points far away from each other, even farther than it is physically possible for the researchers to measure indoors. Without these grid cells, we are not able to understand or remember locations and where we are in relation to where we have been. We make these patterns wherever we go – wherever we stand, lie, or drive.

"We sent the rats into a ten-armed maze, and it turned out that they continued to make the grid pattern but also started a new one for each 'arm.' We believe that these patterns are patched together, so that the rats remember how to get through the maze," Edvard Moser says.

Since then, other researchers have found the same result in patients undergoing epilepsy surgery. It was as anticipated: in humans, as in rats, all locations are stored in a hexagonal pattern. We are all bees! We all organize the world around us as a hexagonal grid.

"We believe that this was developed very early in the evolution of mammals," Edvard Moser says. "And we believe that what we have discovered about grid cells is central for episodic memory. It is, after all, impossible to create memories without tying them to a place."

Other researchers agree that place and grid cells play a special role in episodic memory. Some go so far as to say that this system in the hippocampus and the entorhinal cortex has become specialized to assign each memory its unique memory trace, as part of a unique memory network. Perhaps, at first, the sense of place was the primary task for the hippocampus and the entorhinal cortex. But as evolution proceeded, our memory maps were given a new function: to take our individual experiences and tie them together in a grid. Hexagonal maps of the environment became hexagonal-patterned fishnets of memories.

Recently, researchers in California have been able to demonstrate, in the hippocampi of mice, how memory networks link themselves to context-dependent memory. Like Terje Lømo, they made a window into the hippocampus, to the tiny little piece of it called cornu ammonis, Ammon's horn. Looking at the hippocampus in cross-section, it looks like a goat's horn, bent inward, into a spiral. Here, through the tiny window into the cradle of memory, the California researchers could see, under a slightly fancy microscope, how the neurons lit up when the mice were placed in different environments. They made three different cages, which would give rise to three different memories: a round cage, a triangular cage, and a square cage. The smell, texture, and other conditions also varied between the three cages. The crucial factor was how close in time the various experiences took place. Two groups of mice were compared. Half of the mice had a go at the triangular cage, and then directly afterward they were placed in the square cage. These mice got to experience two different cages in quick succession. The rest of the mice were placed in the round cage and then, seven days later, in the square cage. The second group of mice had two experiences – episodic memories – distinctly separated in time. When the researchers watched through the microscope while the mice were exploring the cages, they could see activity in the neurons in a defined area. Each of the three cages created a signature pattern of neuronal activity in the hippocampus, meaning distinct memories. The exciting part was that the experiences that took place close together in time led to activity in groups of neurons that overlapped. These two experiences hooked on to each other, not only in time but also in place, in the hippocampus of the mice. Meanwhile, when mice visited two cages a week apart, it was accompanied by activity in two separate groups of neurons in the hippocampus. The researchers believe this happens because the activation of the one group of neurons causes other nearby neurons to become easier to activate. Everything links together in a network. The main point of Godden and Baddeley's context-dependent memory experiment has, in this way, been demonstrated in the brain – not in diving mice, but by diving into the cortex of the mice.

When we experience something – as we find ourselves in a specific situation at a specific location – and it becomes a memory in the brain, it spreads out across the cortex until we recall it. A memory is composed of thousands of connections between neurons; it is not one connection that makes a memory. A memory is more than Terje Lømo's long-term potentiation.

But what does a memory look like? Can we see a complex memory the way we can see a simple memory trace? To be able to do this, we must exit the rabbit and mouse brains and enter the human brain. And we must watch the brain while memories are recalled. Fortunately, we don't need to sedate humans and open their heads to get a glimpse of their memories. As we learned in chapter 1, Eleanor Maguire at University College London has used an MRI scanner and some reminiscing volunteers to observe the traces of their memories as they relive their past experiences.

An MRI machine uses a strong magnetic field to take pictures of the body. Different body tissues react differently to the magnetic field, which results in detailed images. The MRI machine can be programmed in a certain way to read the oxygen level in the blood flowing through the brain. Since neurons use oxygen to function, we can tell from the images where there's a lot of activity. We then know where in the brain nerve cells are most active while the test subjects remember things. This is called functional magnetic resonance imaging (fMRI) – images of the brain while it is working – as opposed to structural MRI, which shows us only what the brain looks like. The memories light up like tiny flashlights underwater, flashes that light up the sea in little spurts.

But is it really possible to see what memory a person is recalling? In Eleanor Maguire's laboratory, participants allowed themselves to be scanned by an MRI machine at the same time as they were asked to remember their own experiences. The professor actually managed to figure out what they remembered by studying the fMRI images. Maguire watched the activity in the hippocampus while the test subjects were thinking of episodes from their past, and she could see that each memory had a unique pattern of activity. She had a computer program that learned which of the test subjects' memories were tied to which patterns of activity. From that, the computer program could pick out which fMRI images hung together with which memories. Is this simply a mind-reading machine?

"These are memories we had agreed with the volunteers, before the scanning took place, that they would recall, not random memories. In a way it's, in very general terms, a kind of voluntary 'memory' reading," Eleanor Maguire says.

So far, she can see the track in the vinyl record, but she can't hear the music.

"The next step would be to be able to see what people remember without having decided on a fixed set of memories beforehand. But it's a long way until we get to that level," she assures us. We can safely leave mind reading to science fiction films and books.

Maguire isn't doing this because she thinks memories can be reduced to a checkerboard pattern in an MRI image. To her, memories are vastly complex – they are unique experiences that can only be fully known by the one who keeps them. They are also not static. She has observed that something happens to memory traces over time: two weeks after an initial memory is encoded, its memory trace is visible in the front of the hippocampus, but much older memories from ten years previous are processed further back in the hippocampus.

"Memories contain many pieces of the initial experience that are later brought back and put together again," she explains. "When the memories are still fresh, they are more easily accessible; we can easily picture the episode and how it happened. In the beginning, it is readily available within the hippocampus. As a memory ages, the pieces are stored in other parts of the brain and it takes more effort to reconstruct it and bring it back. The hippocampus puts all the pieces together in a coherent scene."

But what is she actually looking at? What gives the memories a unique "signature" in the fMRI images of the hippocampus? Eleanor Maguire believes that there are groups of neurons working together on one memory.

"The fact that we can see unique patterns for each memory must mean that information about the person's experience is present there; it has to be in some way related to the biological memory trace."       

But because the resolution of an fMRI image is extremely coarse, we can only see large groups of nerve cells activated at the same time, as opposed to individual neurons.

"While it is important to study memory on a cellular level, we should also think of a memory rather like a big cloud of activity. A memory is more than the single synapses – it is much more complex than that," says Maguire.

To her, episodic memories are first and foremost about scenes. "All the little pieces that together make up a memory don't mean anything unless they are placed in a scene. The action takes place somewhere."

But as an episode is tied to a place and forms a scene in your mind's eye, an important component of this may be a set of grids – the map within the hippocampus and entorhinal cortex. The memory is tied down by all the little synapses being strengthened through long-term potentiation. Synapse by synapse, the memories are clicked into place.

"We are hoping that our discovery can help solve the enigma of Alzheimer's disease. Long before there are other symptoms, people with Alzheimer's experience spatial navigation problems," Edvard Moser says. The newest episodic memories also suffer first when the disease sets in. They go before all the knowledge we have gathered throughout life does, and also long before mature memories from long ago dissolve, like clouds of sparkling particles that swirl out to sea, never to return.

But what about our divers? You haven't forgotten, have you, that we sent ten men down into the ice-cold water of the Oslo Fjord at the beginning of this chapter?

The rain is dripping from the eaves of the diving center here on dry land, and we're rubbing our cold and wet hands together in a futile attempt to stay warm, our teeth chattering. The divers are, of course, voluntary participants; nobody is forcing them to do this. Still, with only a few remaining bubbles on the surface reminding us that they are down there, it's easy to be a bit worried. What if something were to happen? And what if they remember as poorly as, well, a jellyfish? We will return to the divers shortly, but since we brought it up: Do jellyfish remember?

"We don't know if jellyfish remember," biologist Dag O. Hessen says. "But jellyfish do have a kind of 'will,' since they swim in a certain direction, even if they don't have a brain, only nerve fibers. However, all animals, even the simplest ones, have a certain capability to learn."

How did human memory become as advanced as it is? Why do we remember the way we do and not the way jellyfish do? What might the alternatives have been?

"We have not been able to prove that animals have memories that work like human memories. We believe that other animals' memories associate to a situation and pop up when they see or feel something, as when for example a cat sees a cupboard door and remembers that it hurt its tail there once," Hessen explains.

So there's no proof that zebras can stare melancholically into the sunset and remember the great loves of their lives, or that a dog can suddenly bark mournfully because it's thinking of a sad episode from its youth. No gazelles cringe because they're thinking about an embarrassing moment two years ago, no leopards experience a flash of happiness when a memory hits them of how they killed their first prey. At least, not that we have been able to prove.

"We believe that only humans do this: look back in time regardless of context. All animals and plants have some form of memory, in the sense that they adapt to the environment. It's beneficial to learn to avoid dangers and remember how to secure food and partners. It's obviously an evolutionary advantage for all living organisms, even for short-lived ones, to be able to remember and not only live in the moment. What's special about humans is our ability both to see the past before us and to create visions of the future. To be able to envision the future is possibly a byproduct of memory," Hessen believes.

The biologist suggests that there's another reason for humans to have developed a large brain with advanced memory, something that has to do with our social groups. "We know that social animals have larger brains and more memory than animals that aren't social animals."

An example: all bats are, in a sense, social animals, but vampire bats are particularly social. They live in groups, and they can't survive for more than three days without fresh blood. According to Hessen, researchers have found that bats – sympathetically enough – help each other by regurgitating blood for others, even bats outside their family, and it seems as if they remember favors that have been done for them earlier. There's a form of reciprocity between vampire bats that's very similar to humans, like friendship.

"Many believe that humans have good memory because people are social animals with many hierarchies and exchanges of favors. Sympathies and antipathies depend on remembering. And the longer one lives, the more one has to remember complicated social structures," says Hessen. Animals that live longer remember more. An example is the elephant. It does actually remember – like an elephant.

This is just one of many anecdotes about elephant memory. In 1999, as the zookeepers in the elephant sanctuary at Hohenwald, Tennessee, introduced their elephant Jenny to a newcomer named Shirley, Jenny became agitated. Shirley also seemed more than usually preoccupied with Jenny. The two elephants behaved as if they knew each other. Upon investigation it turned out that, for a short while more than twenty years earlier, the two elephants had worked together in the touring Carson & Barnes Circus. According to Hessen, researchers that have followed elephants over long periods of time have found that elephant herds are highly dependent on good memory. The matriarch of the herd must be old enough to have the experience to lead her herd to safety if there is a fire or to find water during dry spells; younger matriarchs risk making fatal mistakes.

The elephants Shirley and Jenny acted as if they really had human-like emotional memories of each other. But memories can also be far less complicated, without being less impressive. Several animals have a kind of instinct – or memory – for time and place. Puffins return to the west coast of Norway on exactly the same date year after year, regardless of weather. American and European eels swim all the way to the Sargasso Sea to spawn. Monarch butterflies have multiple generations each year, of which only one lives long enough to migrate south and back. It's impossible for the new generation of migrating monarchs to remember where their great-great-grandparents came from, but still they know to go south to particular wintering grounds. Is this memory or instinct? And can instinct be tied to a certain geographic location or a certain date?

"When the salmon returns to the spawning grounds it came from, it uses its sense of smell, and the sense of smell is closely related to memory in most animals. But there's a lot about animals' memory that's still a mystery to us, as for example this thing about the eel," Dag O. Hessen says.

Even in the human brain, the so-called olfactory bulb is situated close to the hippocampus, pointing to the fact that smell is the sense most closely tied to memory. This doesn't mean that the other senses aren't strong too. Marcel Proust came up with his seven-volume work when he tasted a madeleine cookie dipped in tea. For many, sounds and music are tied to strong memories; just think of how an advertising jingle can stick in your memory. How many thousands of tunes are we familiar with?

Songbirds are birds with good memory. Just like us, they have to learn tunes – they aren't born with them. A songbird placed in some other songbird's nest will learn the wrong tune; a blue tit that is placed in the nest of great tits will learn the great tit's tune. The songs of songbirds can have both dialects and other variants. The European pied flycatcher, for example, varies its tune according to its intended recipient: the "wife" or a "mistress." What makes a bird's memory especially impressive is its brain. Birds have several song centers in their brains, one of which is the higher vocal control center, which grows each spring and has almost completely receded again by the fall!

"We don't know why it happens, because the birds remember the tune they've learned even without the higher vocal control center," ornithologist Helene Lampe at the University of Oslo tells us. There is still a lot scientists don't know about this avian brain region. Female birds typically don't have particularly well-developed higher vocal control centers yet are still able to sing. It's believed they have it so they can identify and remember rivals, but in the case of the European pied flycatcher, it does the female no good; she watches the nest while the male is out looking for more "mistresses."

"This is a songbird mystery we still haven't solved. We don't know where the song is actually stored, but recent research points to the auditory center of the brain being used for some storage," Lampe says.

Many types of birds remember amazingly well: migratory birds remember where to go, parrots and crows can learn human language, and jays that cache food find their way back to their stashed nuts.

"Hoarding requires a good episodic memory – that is, having a vivid memory of the act of burying the nuts. Remembering this experience makes it possible to find them later," Lampe says. Herein lies one of the great controversies in memory research: How uniquely human actually is episodic memory, and can we find evidence that other animals and birds also have this form of memory? Scientists don't have a final answer.

We take our way of remembering for granted. The human, or mammalian, way of connecting experiences through long-term potentiation, creating large memory networks that are kept in place by the hippocampus, could be just one way of doing it. Nature has a wealth of alternatives to offer. Animals without hippocampi also have memory. Even one-celled animals, like slime molds (Mycetozoa), show signs of remembering. In one experiment, researchers exposed a slime mold to moisture and drought on a regular basis and watched it react. After a while, they stopped stimulating it this way, but it kept reacting at the same intervals as before, for quite some time. Slime molds have even found the quickest way through a simple maze! Amoebas leave slime where they've been, so that they don't reenter a dead end in the maze but rather explore new paths. They wander through the maze with their one-celled memory, never knowing that evolution has raced past them.

Slime molds, jellyfish, songbirds, eels, monarch butterflies, vampire bats, puffins, and elephants represent different mysteries when it comes to memory. Which ones have memory, and which just have instinct? They each show us that there are many ways nature can meet the need to keep information for later use. But human memory is perhaps the greatest and most complex. What other animals remember episodes from not only their own lives but also their ancestors' lives from many thousands of generations ago, and record their memories for others to read and remember?

There are enough mysteries within our own memories to keep us busy. Take, for example, Henry Molaison, who opened up so much research into memory: How could the man without hippocampi remember his life before the surgery? As we know, memories appear in the hippocampus when we retrieve them; they light up on the screen of Eleanor Maguire's MRI machine, where they create different patterns. How was it possible for Henry to remember anything at all without his hippocampus, when it is the hippocampus that reassembles memories? This is something memory researchers are still fighting about. The fight is as big as the battle about the role of the hippocampus in memory.

Henry's memories prior to the surgery had gone into storage the normal way, with the help of the hippocampus. His memories had consolidated as memory traces tied experiences together. Later, the synapses in his cortex were strengthened, until they could manage without the help of the hippocampus. This process may take many years. That's why Henry didn't remember anything from the last couple of years prior to the surgery. The memories from this period were simply too unstable and dependent on the hippocampus. For a long time, it was believed that this was the full explanation and that the hippocampus wasn't necessary at all when it came to recalling early memories. But then researchers, like Eleanor Maguire and others, started to notice that things happen in the hippocampus when we retrieve a memory.

They didn't question whether or not Henry's memories were real, but they did point out that a memory is not just a memory. A memory may have turned into a story that includes facts about what happened, not unlike an anecdote. On the other hand, a memory can also be something completely different: a re-creation of the experience, filled with sensory experiences, emotions, and details of how the episode unfolded in time and space. Henry's memories were probably more like the first kind, resembling book knowledge or simple tales, called semantic memory. He seldom gave particularly detailed descriptions of his childhood. Often, the stories began with "I used to . . . ," followed by facts about where he'd gone to school, where he'd vacationed, and who his family was. He possessed a rather dry encyclopedia about himself. Presumably, he could not recall lifelike, smelly, noisy, emotional memories. After having known Henry for years, researcher Suzanne Corkin was convinced that his memories lacked the vividness so characteristic of episodic memories.

***        

Back at Gylte Diving Center, we've split the divers into two groups and numbered them from one to ten. The divers are completing their first memory test, the one we use for comparison, measuring their normal memory. The men are visibly sweating over the twenty-five words we gave them to remember. Not only because the test is hard; they have to look at their list of words for two minutes, then go for a little walk and return to the table to write down what they remember. But with the diving gear already halfway on, they are hot and perspiring more than they might like. The divers manage to remember between six and seventeen correct words, completely normal results.

That day by the fjord, the rain on our skin feels like pins and needles of nervousness as the first group goes down into the water. What if we don't find out anything at all? What if the men are diving in vain and don't get to prove anything about memory and context?

Of course, we can't go through life relying on our surroundings to help us remember everything. Godden and Baddeley also pointed out that this was an unreasonable idea. In An Essay Concerning Human Understanding (originally published in 1689), the philosopher John Locke described a man learning to dance in a room with a large trunk. He could do the most elegant dance steps, but only as long as the trunk was there. If he was in a room without the trunk, he was hopeless on the dance floor. This sounds very strange, and fortunately the story probably isn't true. It highlights, though, the idea of context-dependent memory. The point Godden and Baddeley made was that our memory may rely on context to a certain degree. Can this be useful in some way? Should we cram for an exam in the location where we'll be taking it? Or remain in the same apartment until our dying day for fear of losing the memories that have been made there?

Fortunately, we do have access to our memories when we are not in the same environment as where we experienced an event. The divers at Gylte can recount the amazing experiences they've had in the water even when they are safely on shore.

Our memory networks – our fishnets of memories – benefit from context beyond just our physical surroundings. We create the strongest memory networks on our own, when we learn something truly meaningful and make an effort to understand it. Someone who is passionate about a particular subject, such as diving, will more easily learn new things about diving than about something she's never been interested in before. This is because she already has a large memory network devoted to diving where she can store her new knowledge, and because she is motivated. It's as if we can add another layer of netting just because the self is involved; memory is self-serving. Memories are linked to what concerns you, what you feel, what you want. Too bad, then, that so much of what we actually need to remember is so darned uninteresting!

Lately, others have tried to test context-dependent memory in other ways. Do we remember things we learn while skydiving? The researchers concluded that the stress level of skydivers was so high that it erased all effects of context. This may not be so strange—if we are so high on adrenaline that we barely notice where we are, there are no surroundings to support those memories. More practical were the researchers who wanted to examine if medical students remembered more when they were in the classroom where they had first been taught. The classroom, in this case, was either an ordinary classroom or an operating theater, where the students were dressed for surgery. Fortunately for the future patients of those medical students, it turned out in the experiment that the differences were so minimal that doctors can safely continue practicing medicine far from the context of learning.

In our experiment at Gylte, we split the divers into two groups. The divers in the first group would be tested on what they remembered on land after trying to memorize twenty-five words underwater. The others had to both learn and recall the words underwater.

The five divers in the first group come ashore, splashing as they go. They wriggle out of their masks and flippers, unhook leaden oxygen tanks and sit, legs spread apart, on the bench along the wall of the Diving Center.

The results are miserable.

One of them remembered only words from the first test – the one for comparison – and got a zero on the underwater words. The best one remembered thirteen words from the list he saw underwater, but this too was worse than he'd done during the first test on land. The average result of the comparison test, inside the Diving Center, was 8.6 correct words. The divers remembered an average of 4.4 words when they emerged from the water.

"I sort of thought I had the words there while I was underwater, but then we got up on land, and it was as if my mind changed completely, and I lost it," one of the divers says.

The removing of flippers, tottering up from the edge of the pier along the walk to the Diving Center, lifting the tanks from their backs, and grabbing a piece of paper may of course have disturbed their trains of thought and pushed the words out of the way. Duncan Godden and Alan Baddeley had pondered this possibility and tested whether all the trouble of getting back onto dry land could have thrown off the result. They let one group of divers learn the words on land, then dive and come up again, and compared them with a group who'd learned the words on land and waited the same amount of time, but without moving. The group that dived in the middle remembered just as much as those who had remained still in the same place. So all the hassle of changing location could not have explained why the divers who learned in the water remembered less on land.

Deep beneath the surface, the divers in the second group have taken out their flashlights and waterproof notepads that make it possible for them to write underwater. Bubbles from their breathing pop on the water's surface; they are fifty or fifty-five feet down, and it's hard to handle the plastic-covered sheet to write the twenty-five new words. They've gathered in a circle in the dark, and short flashes from the flashlights tied to their arms shine through the water every time they move their hands and write. Like the words they learned on land, these are mainly one-syllable words: short and concrete and easy to write with gloves on.

This group had remembered an average of 9.2 words when they were tested in the Diving Center. But what happened when they tried to learn twenty-five words underwater and were supposed to remember them underwater? As the bubbles grow bigger and the divers slowly rise to the surface, those of us on the pier are long since soaked through and clinging to empty and wet paper coffee cups. Even the seagulls have stayed at home today.

The divers, on the other hand, are not in a hurry. They rest for a while a few feet under the surface before they get out of the water. Around us, clumps of old snow lie between tufts of rotten grass. Our excitement has been building this whole ice-cold morning, as has our longing for hot chocolate and dry socks; the divers, however, are satisfied with their dive. They proudly hand us their notes.

When we examine the results, it occurs to us that we have managed to re-create the experiment from the 1970s almost down to the smallest detail. The divers who were supposed to learn and remember underwater have remembered on average 8.4 words in the deep, almost matching their achievement on land earlier that day. They pulled this off despite factors like increased pressure underwater, gas mixtures and masks and wet suits and the sound of breathing, clouds of bubbles swirling toward the surface, flashes from flashlights sweeping the bottom of the sea, blurry vision, uncomfortable wet gloves, and difficulties holding pens and waterproof notepads. In the famous experiment from the 1970s, it was clear that the context had an obvious effect – the divers had remembered the list of words much better in the water when they had also memorized it in the water. Actually, they remembered it equally as well as the list they memorized and recalled on land.

When the divers were in the water, they recognized where they had been before, and this memory triggered the memories of what they had learned, so that the words popped up almost by themselves, like images on a screen.

Caterina Cattaneo led the divers in our experiment. She has almost thirty years of underwater experience and has dived at a depth of two hundred feet. This was a simple dive for her. The water temperature was comfortable, she claims, as she swings herself up on the pier and wrestles herself out of her diving mask. The February rain sprinkles the fjord behind her.

"I've never seen seahorses here," she tells us. "I've seen two on Madeira. They were tiny and very cute. They bobbed up and down, their tails wound around a sea plant. But the current was strong, and suddenly I was far away from them. I only caught a glimpse of them."

Excerpted from Adventures in Memory: The Science and Secrets of Remembering and Forgetting by Hilde Østby and Ylva Østby (November 2018, Greystone Books). Reproduced with permission from the publisher.