Adventures in Memory. Hilde østby
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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