Like humans, octopuses have an episodic memory that allows them to recall events from their past. But their memories can also be deceptive. This is shown by a study in which researchers deliberately tried to give octopuses false memories about which container their food is in. The results provide new insights into how the memory of these intelligent cephalopods works.
When we remember an event from our life, complex processes take place in our brain. Our brain does not store the experience as a single memory, but in the form of numerous fragments that it reassembles each time we think back to the situation. Normally, this process works quite reliably. But especially if we have experienced a similar situation within a short period of time, we can confuse characteristics of the two experiences – so-called false memories arise. These are a typical indication of the reconstructive processes that take place when we remember.
Memory test for octopuses
For the first time, researchers have now proven that false memories also occur in squid. A team led by Lisa Poncet from the University of Caen in France used a trick to do this: “To investigate whether the episodic memory of squid is based on reconstructive processes like in humans, we developed a protocol that promotes the formation of false memories,” explain Poncet and her colleagues. To do this, they first showed 15 squid three containers that were marked with different patterns to make them easier to recognize. One container contained shrimp, the squid’s favorite food, another contained crabs, which the squid eat but are less fond of, and a third was empty.
Shortly afterwards, the researchers created a similar situation again, but only the pattern of the cans was visible, not the contents. In a non-confusing control scenario, they presented the shrimp container again, combined with the shrimp scent. For two confusing scenarios, they showed the shrimp container and the empty container together, once with and once without the shrimp scent. “The aim of the misleading conditions was to create an overlap in memory between the contents of the shrimp can and the empty can, so that the octopuses then thought that there were shrimp in the empty can,” the researchers explain.
Overlaid memories
One hour after this exposure, Poncet and her colleagues tested the octopuses’ memory. Unlike before, this time the octopuses were given free access to the containers, but they were only given the choice between the empty container and the one with the less popular crabs. The idea behind this was that if the octopuses remembered the contents correctly, they would choose the crab container over no food at all. If they remembered incorrectly, they might think that the empty container contained shrimp, which would lead them to choose that.
And indeed, in the non-deceptive scenario, twelve of the 15 octopuses chose the crab container as expected. However, if they had previously seen the shrimp container and the empty container without any smell together, they chose the empty container in half of the cases – an indication of a false memory. In the deceptive scenario with smell, the results were ambiguous: ten of the 15 animals chose the crab container, four chose the empty one, and one looked at both containers but did not make a decision within ten minutes.
Individual differences
“Our results suggest that squid form false memories for visual impressions, but not for smells,” explain Poncet and her colleagues. “These memory errors could be the first indication of the presence of reconstructive processes in the memory of cephalopods.” One limitation of the study is that the individual squid could not be tested multiple times under the different conditions. “Multiple repetitions would have influenced the animals’ later decisions,” says the team. Therefore, it remains unclear whether the decision to choose the empty can was a one-off oversight or a systematic error.
However, the team believes that the results suggest that some individuals are more susceptible to false memories than others. “Some did not seem to be affected when exposed to a misleading event, while others formed false memories,” says Poncet’s colleague Christelle Jozet-Alves. “This phenomenon is also found in humans.”
Source: Lisa Poncet (Normandie University, Caen, France) et al., iScience, doi: 10.1016/j.isci.2024.110322