Cuttlefish, with their blimp-shaped bodies and eight squiggly arms, don’t age like people do. Sexual maturity tends to come late for them—about three-quarters of the way through their two-year lives, the rough equivalent of a human hitting puberty in their 60s. The geriatric cephalopods will then spend several weeks on an absolute bender, coupling up with as many partners as they can. Only after the close of these frenetic sexual bonanzas does true decrepitude come to claim them: Their feeding tentacles go limp; their appetite deserts them; their color-changing skin flickers like a television on the fritz. The animals pivot almost instantaneously from their sexual prime into the throes of infirmity, and within days, they are dead. “They really go out with a bang,” Alex Schnell, a cuttlefish biologist at the University of Cambridge and the Marine Biological Laboratory, in Massachusetts, told me.
Before this rapid denouement, though, the animals stay relatively sound of body—and also of mind. Schnell and her colleagues have found that common cuttlefish (Sepia officinalis) can still form and retain crystal-clear memories of personal experiences just a month before their death. They can catalog the what, when, and where of recent events, and use that knowledge to inform their actions in the present. It’s an animal approximation of what’s called episodic memory in humans, an ability that’s often billed as a sort of mental time travel that allows creatures to relive past experiences. For us, episodic memory usually starts to fade around retirement age. But the cuttlefish version appears to persist deep into their golden months. “I’m not familiar with any other animal model that has shown episodic-like memory still intact” this late in life, Gabriel Nah, a neurobiologist who studies rat memory at Indiana University and wasn’t involved in Schnell’s work, told me.
That cuttlefish can form episodic-like memories at any age is remarkable. Among humans, episodic memories are the source of subjective knowledge that can’t be found in textbooks or Google searches; they live in the world of personal storytelling, each unique to the individual who crafts them. Until the late 1990s, researchers had no evidence that nonhuman animals could manage even the basics of this kind of recall.
That all changed when Nicky Clayton and Anthony Dickinson, researchers at the University of Cambridge, showed that western scrub jays could remember when and where they’d hidden particular caches of food, and knew to avoid retrieving nosh that had been hidden long enough to rot. What the birds accomplished wasn’t necessarily an exact echo of the emotive, self-conscious remembering that humans engage in when, say, waxing nostalgic about a first date. But all the mental ingredients, at least, seemed to be there.
In the two decades since, the club of what-when-where rememberers has grown to include more birds, rodents, dogs, and others. Common cuttlefish, already famous for their big, sophisticated brains, became card-carrying members in 2013, when a team led by Clayton and Christelle Jozet-Alves showed that laboratory-raised cephalopods could keep track of what, when, and where they’d eaten after researchers offered them snacks in sequence, like a mental food journal. Schnell picked up the project a few years ago, and became curious about whether their abilities could withstand the ravages of time. Among humans, episodic memory “is one of the first types of memory that starts to deteriorate as an individual gets older,” she told me. But in a series of tricky trials designed by Schnell and her colleagues, both middle-aged cuttlefish, about 10 to 12 months old, and elderly, postpubescent cuttlefish, 22 to 24 months old and just weeks away from death, kept their wits about them.
The researchers first had the cephalopods prove that they could memorize a feeding routine, tapping into a different form of memory, called semantic memory, that deals in general facts and concepts and stays intact in elderly humans. The cuttlefish successfully learned to swim to specific locations in their tank marked with identical black-and-white symbols to earn edible rewards at different times of day—the equivalent of chowing down in a breakfast nook in the morning, a kitchen counter at noon, and a formal dining room in the evening.
Then came the tougher test. The researchers trained six new animals in each age group to link the same black-and-white symbol to two types of food: live grass shrimp, a luxury food item for cuttlefish, or a boring lump of prawn meat. In the morning, the cuttlefish would get a selection of both seafoods at once, each in its own location in the tank. They’d then get a second feeding, either an hour later, with only the less desirable menu item, or three hours later, with both options available.
In the one-hour case, the cuttlefish had to swim up to the location where the breakfast prawn was offered to earn the second meal. If three hours had passed, they could hang out at the shrimp spot for a tastier reward. (Cuttlefish, apparently, can tell what time of day it is, and no one yet knows how.) In short, the cuttlefish had to match what they’d eaten for breakfast to where the grub had first appeared, all while calculating how much time had passed since their last feeding. Each day of the experiment, the prawn and shrimp feeding spots moved around. So the cuttlefish had to rely on their personal experiences of their morning meal, and adjust accordingly.
Most elderly people, Schnell said, would have flunked a human version of the team’s experiments. But all of the cuttlefish passed, “an incredibly complex thing for an animal to do,” Robyn Crook, a neurobiologist and cephalopod expert at San Francisco State University who wasn’t involved in the study, told me. If anything, Schnell said, the older ones were faster at learning the rules and applying them in new contexts, which is “pretty mind-blowing.”
Wild cuttlefish don’t hunt by sidling up to black-and-white symbols in laboratory tanks. But Schnell and Clayton think the skills the cephalopods showed off in these experiments might translate to hunting, or even their over-the-hill orgies. Replaying personal memories in their head could, for instance, help the animals keep track of which reefs crawl with crabs at dusk, or which males or females they’ve already boinked. And, of course, revisiting memories isn’t just about the past. Cuttlefish might be among the few animals that have enough cognitive ammunition to use those memories to plan ahead. Previous research by Schnell and others has shown that the cephalopods will pass over mediocre foods if they know better options are coming—a form of self-control that takes human children years to develop in full.
Adapting human concepts and experiments to other animals is always a tricky business, not least because other species’ wants and needs, and the cleverness they need to navigate them, differ so much from ours. Some researchers remain skeptical that what-when-where memory, impressive though it may be, even counts as episodic-like. Jennifer Vonk, an animal-cognition expert at Oakland University, in Michigan, who wasn’t involved in the study, told me it’s possible that the task assigned to the cuttlefish “wasn’t challenging enough” to really push the limits of their personal recall. Under more natural circumstances, with more distractions, the cephalopods’ weak spots might have shown more clearly.
Older cuttlefish, after all, aren’t totally impervious to aging. Though fit enough for repeated bouts of sex, they still show slight signs of wear and tear: slower reflexes, a blunted interest in food, a haggardness in their skin. Schnell sees this happening even in virgin cuttlefish, raised in the lab, which reach their final days without getting the chance to mate. Trevor Wardill, who studies cuttlefish vision at the University of Minnesota and was not involved in Schnell’s study, told me that he’s noticed that aged animals struggle to strike at faux prey in certain hunting simulations. Papers from the 1990s suggest that elderly cuttlefish might also have trouble holding on to memories long-term.
In some ways, it’s hard to define what aging really is, in cuttlefish terms. Humans are used to “a long period of maturity and a slow decline into senescence,” Jennifer Mather, a cuttlefish biologist at the University of Lethbridge, in Canada, who wasn’t involved in the study, told me. Cephalopods take a more meandering path to adulthood, speed through their sexually active stint, then “swiftly decline.” (Crook also pointed out that sex, which these cuttlefish didn’t have, might hasten the aging process.) Had the team tested the cuttlefish in their last couple days of existence—something that would have been very difficult to do—they might have found very different results. Age and aging aren’t always the same: Perhaps the study’s elderly cuttlefish aren’t surprisingly sharp, but simply typical adults, acting exactly as old as they should.