Octopuses have been called a “second genesis” of intelligence, that is, they are invertebrates with high intelligence, instead of vertebrates. But their close relatives, squid and cuttlefish (they are all cephalopods), are not far behind, according to recent research. One unusual finding is that cuttlefish have very good memories:
Can you remember what you had for dinner last Tuesday? Or on this day last year? It turns out that cuttlefish can, right up to old age – the first animal we’ve found that doesn’t show signs of deterioration in memory function over time.David Nield, “The Incredible Brains of Cuttlefish Hold Memories That Never Seem to Fade” at ScienceAlert (18 August 2021)
Of course, cuttlefish live only a couple of years, which makes them useful study subjects. In addition, food may be one of the few subjects they must think about. They do not mate until near the end of their lives.
What’s unique about them is not just a good memory but the fact that their memory does not appear to deteriorate with age:
Evidence of episodic-like memory has been observed in other animals, including rats and jays, but the researchers say there’s something about cuttlefish that sets them apart at the moment: not seeing these memories deteriorate as they get older.
That might be because, unlike humans and other vertebrates, cuttlefish brains don’t have a hippocampus – which is closely linked to memory. Learning and memory do decline in cuttlefish, but only two or three days before death.David Nield, “The Incredible Brains of Cuttlefish Hold Memories That Never Seem to Fade” at ScienceAlert (18 August 2021)
Deterioration of the hippocampus is considered a significant cause of memory loss in humans.
The test required genuine memory:
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.Natalie Grover, “Cuttlefish remember details of their last meal, study finds” at The Guardian (18 August 2021)
The paper is open access.
Surprisingly complex traits have recently been discovered in other cephalopods as well. For example, researchers have reported that octopuses sleep, in the same sense that reptiles and birds do, with active and quiet cycles:
The team observed that colors disappear from the octopuses’ skin during “quiet sleep,” and their pupils contract into thin slits. In this state, the animals become quite still except for the occasional soft, slow movements of their suckers and arm tips. Periods of quiet sleep can last from a few minutes to about half an hour…
“It really resembles what you see in reptiles and birds: Long, quiet sleep followed by short, brief episodes of active sleep,” Ribeiro said. Mammalian sleep follows a similar pattern but the active sleep, namely REM, typically lasts longer than in other animals, he said.Nicoletta Lanese, “New Study Hints at Human-Like Sleep in Octopuses” at RealClearScience (March 26, 2021)
Do octopuses dream? We can’t really know that but neuroscientist Sidarta Ribeiro told RealClearScience that sleep may play an important role in the octopus’s learning and memory, as it does with humans. That is, it may enable the octopus to process information learned during the day for future use.
A practical outcome of discovering the intelligence of cephalopods is that many are raising questions around their treatment. Some researchers think that the use of the octopus should be governed by the same sorts of rules as govern the use of vertebrates, based on their assumed sensitivity to pain. Pain?
The results show the cephalopods’ complex pain experiences. They associated the chamber they had once liked best with the stinging they felt the last time they were there, even though the injection occurred somewhere else. Then they compared that experience with their typical pain-free state and decided that how they usually felt was better. “That’s the sort of big cognitive leap you have to make to be able to do this particular learning experiment,” Crook says. Using all that information, the octopuses chose to go to the nonpreferred chamber. “There’s a lot of conscious processing that has to happen,” she says.Anna Blaustein, “Octopus ‘Teachers’ Demonstrate They Feel Emotional Pain” at Scientific American (April 23, 2021)
It’s not clear why cephalopods — octopuses, squid, and cuttlefish — are unusually intelligent among invertebrates. One thesis worth considering is that they don’t have shells. Constantly assessing information from their environment is more important to them than it would be to, say, clams and oysters that can simply filter food from flowing water and shut their shells when danger threatens. Also, as ScienceDaily notes, “Without exception all cephalopods are active predators and the ability to locate and capture prey often demands some sort of reasoning power.” Well, anyway, cleverness.
Just how the cephalopods became intelligent is an open question. Many life forms might be better off to be more intelligent but they aren’t. But then, questions like these are part of what makes science fun.
You may also wish to read: Octopuses get emotional about pain, research suggests. The smartest of invertebrates, the octopus, once again prompts us to rethink how we understand the origin of intelligence. The brainy cephalopods behaved about the same as lab rats under similar conditions, raising both neuroscience and ethical issues.
“What neuroscientists now know about how memories are born and die” Where, exactly are our memories? Are modern media destroying them? Could we erase them if we wanted to?