Cuttlefish have one of the largest brains among invertebrates and can remember what, where, and when specific things happened right up to their final days of life, according to new research.
The cephalopods – which have three hearts, eight arms, blue-green blood, regenerating limbs, and the ability to camouflage and exert self-control – only live for roughly two years.
As they get older, they show signs of declining muscle function and appetite, but it appears that no matter their age they can remember what they ate, where and when, and use this to guide their future feeding decisions, said the lead study author, Dr Alexandra Schnell from the University of Cambridge.
This is in contrast to humans, who gradually lose the ability to remember experiences that occurred at a particular time and place with age – for instance, what you ate for lunch last Wednesday. This “episodic memory” and its deterioration is linked to the hippocampus, a seahorse-shaped organ in the part of the brain near our ears. Cuttlefish, meanwhile, do not have a hippocampus, but a “vertical lobe” associated with learning and memory.
In the study, Schnell and her colleagues conducted memory tests in 24 cuttlefish. Half were 10-12 months old (not quite adults) while the rest were 22-24 months old (the equivalent of a human in their 90s), according to the paper, published in the journal Proceedings of the Royal Society B.
In one experiment, both groups of cuttlefish were first trained to approach a specific location in their tank, marked with a flag, and learn that two different foods would be provided at different times. At one spot, the flag was waved and the less-preferred king prawn was provided every hour. Grass shrimp, which they like more, was provided at a different spot where another flag was waved – but only every three hours. This was done for about four weeks, until they learned that waiting for longer meant that they could get their preferred food.
To make sure they hadn’t just learned a pattern, in the testing phase the flags were placed in random locations to denote the preferred food and the not so-preferred food. That information was then meant to be used to work out which feeding spot was best at each subsequent flag-waving, whether one or three hours later.
The placement of the flags was unique to each test day – so, the cuttlefish would have to recall what they ate during the initial feed, where they ate it, and how much time had passed, explained Schnell.
During training, the performance of both groups was comparable, she said. “In the test phase, the older cuttlefish actually outperforms the younger cuttlefish.”
Malcolm Kennedy, professor of natural history at the University of Glasgow, said it was refreshing to come across another case where aspects of animal cognition can be as advanced as our own, despite huge evolutionary time separation and a nervous system constructed completely different from ours.
“The pedestal upon which humans place themselves in terms of neurological abilities continues to crumble. It is just that other types of animals perform similar functions differently,” he said.
Schnell suggested that the preservation of episodic memory in cuttlefish despite their age may be related to the fact that they only breed at the end of their life, and remembering who they mated with, where, and how long ago could help disseminate their genes widely by allowing them to mate with as many partners as possible.
theguardian.com, 18 August 2021