Common cuttlefish retain sharp memories about recent meals, even in their final weeks of life, accordin to a new study published this week in Proceedings of the Royal Society B: Biological Sciences.
Despite showing other signs of aging, elderly cuttlefish can recall memories as well as youngsters. This research is the first time scientists have found evidence of an animal whose ability to remember specific events doesn’t deteriorate with age.
"Cuttlefish can remember what they ate, where and when, and use this to guide their feeding decisions in the future,” says study author Alexandra Schnell, a behavior ecologist at the University of Cambridge and the Marine Biological Laboratory, in Massachusetts, in a press release. “What's surprising is that they don't lose this ability with age, despite showing other signs of aging like loss of muscle function and appetite.”
Though they have “fish” in their name, cuttlefish are a type of tentacled mollusk called a cephalopod, closely related to octopuses and squid. The soft-bodied creatures, which rely on an internal bone called a cuttlebone to control their buoyancy, include more than 100 different species. Because they lack external armor, they use their impressive intelligence and camouflage abilities to outsmart predators.
Cuttlefish have large brains relative to their body size, and they are among the most intelligent invertebrates known to science. They can learn to solve mazes and puzzles, and even practice self-control and delayed gratification, passing up a less-delicious food item for a tastier treat at a later time, reports Jennifer Ouellette for Ars Technica. This ability to mentally relive past events—called “episodic memory” in humans—is rare outside of intelligent vertebrates like birds and primates. Humans and other animals gradually lose our ability to form clear memories as they age, and researchers were curious if cuttlefish, which have a lifespan of just two years, faced a similar cognitive decline.
The team tested two dozen young and old common cuttlefish—half of which were 10 to 12 months old, just shy of adulthood, and the rest were 22 to 24 months old—to compare their abilities. Scientists marked specific areas in the cuttlefishes’ tank with different black and white symbols and fed them a tasty lump of shrimp or a comparatively bland piece of prawn at each location. After weeks of foraging, the cuttlefish learned when and where certain food rewards were available. When scientists mixed up the feeding patterns, both old and young cuttlefish recalled which type of prey appeared at which station and used that memory to find their preferred meal at the next feeding.
"The old cuttlefish were just as good as the younger ones in the memory task—in fact, many of the older ones did better in the test phase," says Schnell in a press release.
Cuttlefish memory does have a limit—a few days before death, their memory and learning function takes a steep decline. Part of the reason cuttlefish maintain sharp memories late in life might be because they lack a hippocampus, the region associated with memory in humans and other vertebrates, according to Science Alert’s David Neild.
Because cuttlefish only mate at the end of their lives, the team thinks this memory ability may help cuttlefish remember when, where and who they mated with, in an effort to spread their genes far and wide.
“They really go out with a bang,” Schnell tells Katherine J. Wu of the Atlantic.