Some birds can use ‘mental time travel’, study finds

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Quick – what did you have for lunch yesterday? Have you been with someone? Where have you been? Can you imagine the scene? The ability to remember things that happened to you in the past, especially going back and recalling small random details, is a hallmark of what psychologists call episodic memory — and new research suggests it’s an ability humans may share with birds called Eurasian jays.

With episodic memory, “you remember an event or an episode, hence the name,” said James Davies, first author of the study, which was published May 15 in the journal PLOS One. “You kind of go through it mentally. It also includes the other kinds of details that make up that experience, like the sounds, the sights, even your thoughts or your mood at that moment.”

Episodic memory is different from semantic memory, which is the recall of factual information, added Davies, a doctoral student in psychology at the Comparative Cognition Lab at the University of Cambridge.

“It’s often helpful to think of episodic memory as remembering, while semantic memory is just knowing,” he said. “It’s not actually a conscious summoning.

While episodic memory is an integral part of how most people experience the world, it can be difficult for scientists to prove whether non-human animals share this ability—after all, they can’t tell us what they think. For decades, however, scientists have been devising experiments to delve into animals’ ability to remember previous events, and have found evidence of episodic memory in creatures as diverse as pigeons, dogs and cuttlefish.

Corvids – a group of birds that includes crows, ravens and jays – are remarkably smart, and previous studies have suggested they are capable of episodic memory, which can help them find bits of food they’ve stashed away for later. In 1998, Dr. Nicola Clayton devised an experiment with scrubbing jays in which the birds appeared to remember what types of food they had hidden in different places and how long ago.

This way of looking for evidence of episodic recall—called the what, when, where protocol—has become standard among animal memory scientists. But Davies, who is Clayton’s adviser, wanted to find other ways to test this cognitive ability.

“If you’re only using one methodology, then there’s potentially some error in that method,” Davies said. “If you use multiple different methodologies that test the same thing in completely different ways, it leads to much more compelling evidence.”

Scientists have devised a new approach involving Eurasian jays, and what they discovered could have implications for the study of human memory.

Davies and Clayton’s new experimental design drew on the concept of random memory.

“The idea is that with human episodic memory, we remember details of events that weren’t necessarily relevant to anything at the time. We didn’t actively try to remember it,” Davies said. “But if you were asked about it a few days later, you might remember the details.

It’s seemingly unimportant information that you haven’t consciously committed to memory – like remembering what you had for lunch yesterday. This aspect of episodic memory is sometimes called “mental time travel”.

To determine whether Eurasian jays are capable of mental time travel, the researchers worked with birds that had been trained to find food hidden under cups. Davies set up a row of four identical red plastic cups and let the birds watch him place a piece of food under one of the cups. The jays then had to remember under which mug the food was hidden. Easy enough.

In the next step of the experiment, Davies made small changes to the appearance of the cups, such as adding stickers or colored strings, but again hid the food under the same mug in the set. To a bird looking for a treat, these strings and stickers were seemingly unimportant secondary information – at the moment they only had to care about the location of the cup to find food.

But in the final stage of the experiment, these small details of cup decoration became unexpectedly important. Davies changed the position of the cups so that the birds could no longer rely on the once crucial information about which cup in a row contained food. (The treats were removed from the cups in the meantime to rule out the possibility that the birds were finding food by smell alone.) However, after a 10-minute break, the jays were still able to find the treat cups.

Davies suggested that the birds’ mental process may have involved asking, “Where’s the food?” I remember going in with the black square. I’m going to go for it,” Davies said. The jays appeared to go back into their memories to retrieve details of the cup decorations and were very successful at using this information to find hidden food.

“This study provides strong evidence for episodic memory in jays,” said Dr. Jonathon Crystal, provost professor of psychological and brain sciences at the University of Indiana Bloomington, who was not involved in the project. “If you can answer this unexpected question after random encoding, it becomes a strong argument that you can remember back in time to a previous episode, which is at the heart of documenting episodic memory.”

Crystal said studies like this one, which aim to identify animals’ abilities to form episodic memories, are important in part because of their potential role in human memory research.

“The big memory disease is Alzheimer’s disease, and of course the most debilitating aspect of Alzheimer’s disease is the profound loss of episodic memory,” Crystal said.

Because Alzheimer’s drugs for humans always go through animal testing before reaching human trials, he noted, it’s important for scientists to be able to examine whether the drugs actually affect the kind of memories that Alzheimer’s patients lose .

“It’s not enough to just improve memory, we need to improve episodic memory,” he said, and a better understanding of how to test episodic memory in animals could help make that possible.

Kate Golembiewski is a Chicago-based freelance science writer covering zoology, thermodynamics, and death.