Adventures in Memory. Hilde østby
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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