Can dogs remember the past?

It’s the sort of thought that might pass through any dog owner’s mind as they return home from a long workday and are slobbered over by their canine: Can dogs remember the past they share with their humans, and to what extent? Scientists have been exploring the question of dog memory for quite some time, and thankfully, the news is good.

Studying the cognitive abilities of nonhuman animals, dogs included, has never been easy, in no small part due to the fact we can’t truly know what these animals are thinking. Another major problem is that people are very good at reading too much into the gestures of our companions—a tendency likely best exemplified by the story of Clever Hans. Clever Hans was a horse renowned for its apparent math-solving skills in the early 1900s, until psychologist Oskar Pfungst showed that Hans was simply responding to the subtle cues of its owner. To this day, animal behavior scientists try their best to account for the Clever Hans effect and other biases in their research.

It’s also important to distinguish between the different types of memory out there. Semantic memory is the kind that allows us to recall dry facts and knowledge about the world that we’ve previously learned. Most animals and especially mammals are thought to possess semantic memory; in dogs, it lets them remember what to do when their owner says, “Stay!” (assuming they’re successfully trained, at least). But the ability to remember and replay our personal life events and experiences—the experiences that inform our behavior in the future—that’s known as episodic memory. 

Canine cognition

In decades past, some scientists argued that nonhuman animals aren’t capable of episodic memory, perhaps because they lack the sort of self-awareness present in humans. But more recent research has started to undermine this narrative. 

Gregory Berns, a neuroscientist at Emory University who has studied and written about canine cognition, says that dogs and many other animals seem to have the brain anatomy necessary to possess something similar to episodic memory in humans. Probably the single most important brain structure involved in episodic memory is the hippocampus, which acts as a sort of index for our memories, according to Berns.

“Your memories are scattered throughout your brain. And the way the hippocampus works is when you call something up, it kind of replays those things in the rest of your brain. So you can’t do it without the hippocampus,” Berns told Gizmodo. “So, do other animals do that? My guess is yes, they probably do. Because certainly every mammal that we’ve looked at has very similar brain structures; they all have a hippocampus.”

To no one’s surprise, owners certainly think highly of their dog’s memory. A 2020 survey found that the vast majority of dog (and cat) owners reported their pets being able to remember past events, even one-off events that happened years ago. Scientists have also tried to experimentally test for the presence of episodic memory in dogs.

“A key feature of the self”

A 2016 study from a team in Hungary, for instance, found that dogs can watch their owner carry out an action, then mimic that same action when prompted to do so via a specific command (in this case, “Do it!’). While this might look like a typical example of training, the researchers also demonstrated that the dogs could replicate an owner’s actions at a moment’s notice, when the owners shouted “do it” during a different task. For dogs to pull this off, the researchers argued, they would need to remember witnessing someone else’s movements, even when not explicitly trained to, then work out how to perform those same movements with their bodies—a complex feat of cognition indicative of having episodic-like memory. 

The same team of researchers published another study in 2020. This time, they trained dogs to repeat certain actions of their own with a specific command. Then they had owners unexpectedly ask their dogs to repeat other actions, including those performed spontaneously in everyday situations, which the dogs managed to do.

“The combined evidence of representing own actions and using episodic-like memory to recall them suggests a far more complex representation of a key feature of the self than previously attributed to dogs,” the researchers wrote.

Related article: Why are dogs so insanely happy to see us when we get home?

These and other studies, as is often the case with animal behavior research, tend to be based on small sample sizes. Scientists have also only been able to test for specific aspects of cognition tied to episodic memory, not definitively show that dogs have it (after all, dogs can’t talk to us). Dog memory is certainly different in important ways from human remembering as well. Other research has found that dogs and other nonhuman animals tend to have a much shorter memory span in general compared to us, for instance.

But the overall data does point to memory in nonhuman animals as having a lot more in common with human memory than we once thought. Berns notes that scientists have been able to study the brains of rats in much finer detail than those of dogs, finding evidence that they too can replay recent events, such as running through a maze in their heads, even while dreaming.

“I think it’s fairly safe to assume that if that’s going on in rats, it’s most certainly going on in dogs, too,” said Berns, who is also the author of the upcoming book Cowpuppy, a scientific memoir detailing his experiences exploring cow intelligence.

Of course, there are plenty of anecdotes that make the case for sustained dog memory even more compelling. Perhaps the most heartbreaking example is the tale of Hachiko, a Japanese Akita dog born in 1923. 

Hachiko met his owner, Hidesaburo Ueno, at Shibuya Station in Tokyo every day after his commute from work—that is until Ueno tragically died of a cerebral hemorrhage in 1925. Despite his owner’s death, and after he was placed with Ueno’s gardener who lived near his old home, Hachiko would continue to return to the Shibuya Station at the same time as before, every day for the next nine years until his own death in 1935. While Hachiko’s waiting may have been in vain, the eventual discovery of his routine made him a treasured hero in Japan, one still honored annually today. 

Dogs might not remember quite like humans. But the bonds we make with each other do appear to be unforgettable for both parties.