Common Cuttlefish May Form False Memories, Study Suggests

Our memory does a great deal for us, but it is also capable of deceiving us.

Because the brain records information in fragments, details can become muddled when we rebuild a recollection. This can result in what are known as false memories.

For the first time, scientists have now found evidence of false memories in the common cuttlefish, an animal profoundly unlike humans.

The finding may help reveal more about the remarkable and unusual intelligence displayed by cuttlefish (Sepia officinalis), as well as their close cephalopod relatives, including octopuses and, to a smaller extent, squids.

"Our results suggest that cuttlefish do form visual false memories, but not olfactory false memories," writes a team led by neuroethologist Lisa Poncet of the University of Caen Normandy in France. "These memory errors might be the first indication of the presence of reconstructive processes in the memory of cephalopods."

Common cuttlefish intelligence and episodic memory

Earlier studies have produced striking evidence of cuttlefish intelligence. Among other abilities, they have passed a cognitive test developed for human children that measures the capacity to delay gratification. They can also learn to identify shapes and link those shapes to particular rewards.

Crucially for this research, cuttlefish have also demonstrated exceptionally precise and detailed memory recall. These unusual sea creatures can remember what they ate, where they ate it and when they ate it: a degree of detail called episodic memory.

Poncet and her colleagues set out to establish how these memories are retrieved. They wanted to know whether a memory is recovered from the brain as a single, seamless whole or whether, as in humans, the cuttlefish brain reconstructs its components from the locations where they were encoded and stored.

Testing false memories in cuttlefish

False memories can arise when highly similar recollections become confused, so the researchers devised an experiment around that principle. The cuttlefish experienced a sequence of closely related situations involving tubes containing food.

One tube held crab meat, which cuttlefish eat despite it not being their favourite food. A second tube contained shrimp, which cuttlefish particularly enjoy, and the third tube was empty. Every tube carried its own distinctive pattern.

The experiment consisted of three stages.

During the first stage, the cuttlefish were presented with all three tubes, allowing them to view their individual patterns and contents without being able to touch them.

The second stage used one of several possible scenarios. In one, the shrimp tube and the empty tube were placed together; both were empty and turned so that the cuttlefish could not see this. In another, the same two tubes were shown with a shrimp odour present. In a third scenario, an empty shrimp tube was displayed on its own.

For the third stage, each cuttlefish was shown an empty tube alongside a crab-patterned tube, with both once again turned to conceal any contents. The purpose was to determine whether the animal could correctly recall which tube had contained food, or whether a false memory would lead it to select the empty tube because it wrongly believed it held shrimp.

Visual cues appear to create false memories

The findings were not entirely clear-cut, but they indicated that deceptive visual cues could implant false memories. When the second-stage scenario featured only an empty tube, the cuttlefish searched the crab container about 80 percent of the time.

However, after being shown both the shrimp tube and the empty tube in stage two, the cuttlefish were no more successful than chance at locating the crab. It was almost as though they had confused the empty tube with the one that had contained shrimp.

Oddly, introducing a smell into the tank during stage two appeared to prevent false-memory formation. The cuttlefish then chose the crab tube on most occasions. The researchers propose several potential explanations, including that the scent of prey could help the animals avoid constructing false memories.

The team also acknowledges that more straightforward explanations cannot be excluded, such as greater familiarity with the empty tube causing the events to become confused.

This research remains at a very early stage. For now, it indicates only that cuttlefish may retrieve memories in a manner very similar to our own.

Other evidence has suggested that cuttlefish memory could share features with human memory. A 2012 study reported that the common cuttlefish seems to experience REM sleep, a stage linked to memory stabilisation.

This is particularly compelling because cephalopods split from vertebrates about 550 million years ago, and their evolution since then has differed dramatically from that of almost every other organism on Earth. These curious animals may therefore offer much to teach us about the evolution of cognition and intelligence.

One further observation suggested that cuttlefish intelligence may extend beyond what is currently understood, and that the subject deserves additional study.

"What was surprising was that the susceptibility to form false memories seems different between individuals," says Christelle Jozet-Alves of the University of Caen Normandy.

"Some appeared unaffected when exposed to a misleading event while others did form false memories. This phenomenon is commonly found in our own species in which this susceptibility varies among individuals and within individuals."

If there is more tasty shrimp available, the cuttlefish are unlikely to object.

The research has been published in iScience.