Cuttlefish remember what they had for lunch 2 days ago — and don't get forgetful with age, study finds

Cuttlefish don't live long compared to humans, but it turns out they have their own unique gift — their memories don't deteriorate with age the way ours do.

New findings from a team of researchers around the globe, published in the journal Proceedings of the Royal Society B, suggest that cuttlefish can remember details about what they ate for dinner last week, and that ability doesn't decline until the last few days of their lives. 

The findings are first evidence of any animal whose memory of what it did — and when — doesn't diminish with age.

"They specifically remember three things about their meal events, and that's what they ate, where they ate it and how long ago," Alex Schnell, the study's lead author, and a comparative psychologist from the University of Cambridge, told As It Happens guest host Helen Mann.

Schnell has been studying cuttlefish for years because they've got big brains, the largest brain-to-body ratio of all invertebrates, she said. But Schnell also said the fish are "alien in so many other aspects."

"They have blue blood, three hearts, eight arms, a bird beak, and they live very short lives — up to two years in the wild."

Schnell said the team did memory tests on two dozen cuttlefish. 

Come eat at cafe cuttlefish

"So I have to design [the tests] in a way where their behaviours can tell me whether they've solved the task or not," said Schnell. So she used what she called "cuttlefish cafes" set up in their tanks, the locations marked by flags to show where the cuttlefish could find food. 

"One of the cafes offered their favourite meal and the other cafe offered a less preferred meal. They were also open at different times. So the cafe with the less preferred meal would be open more frequently, whereas the cafe with the preferred meal would be open less frequently," she said.

"So in order to make decisions about whether to search for food each afternoon, they would have to recall a specific event that happened that morning about where they ate, what they ate and how much time had passed since their last meal." 

The cuttlefish were offered their less preferred food, a piece of king prawn, and the more preferred, live grass shrimp. 

In order to make sure the cuttlefish weren't just remembering the location, the flags (or cafes) were moved around the tank each day so the cuttlefish would have to watch and see what kind of food appeared at which location.

They have blue blood, three hearts, eight arms, a bird beak, and they live very short lives — up to two years in the wild.- Alex Schnell, researcher 

"We expected a little bit of a decline in memory performance in the older cuttlefish, but we actually saw comparable performance across both age groups," said Schnell. 

They tested cuttlefish that would qualify as middle aged, and those that would be considered quite old and nearing the end of their lives. 

"The older cuttlefish perform just as well as the younger cuttlefish, they even outperformed the younger cuttlefish in part of the test," she said.

Schnell said the findings of memory retention in older cuttlefish are equivalent to a 90-year-old human remembering every detail about what they ate for breakfast that morning or even the day before. 

Episodic vs. semantic memory

In humans (and mammals), memory declines with age, but not all memory functions decline at the same time.

Often, the first to decline is what's known as episodic memory, which is what Schnell was testing in cuttlefish. Episodic memory is the ability to remember things that happened in specific times and places, like where you went on vacation three years ago, or what you did last weekend.

By contrast, semantic memory is the ability to recall something you've learned, like playing the guitar, without it being tied to location or time. This ability tends to remain unimpaired with aging. 

The reason that episodic memory declines in vertebrates like humans and other mammals, is likely due to the deterioration of the hippocampus, the researchers say. Notably, cuttlefish do not have a hippocampus.

Instead, they have what's known as a vertical lobe.

"In a previous study, it was found that this lobe is preserved even at old age. There's no obvious signs of degeneration until, say, the last two or three days of their lives," said Schnell. "We're suggesting that perhaps the preservation of this particular structure allows them to have these crystal-clear memory recollections."

However, there's still more research to do to discover exactly how cuttlefish remember what they do.

One reason could be because the cuttlefish only breed toward the ends of their lives, said Schnell, and they need to breed with as many different partners as possible to spread their genes.

"So we suggest that this really crucial moment in their life might be optimized by remembering who they mated with, where and how long ago," she said.  

Written by Andrea Bellemare. Produced by Kate Cornick.