Psychology defines associative learning as that generated by association between a stimulus and a certain response. A simple example is children's learning that stoves can cause burns: the experience makes the child (or not so young) respect stoves in operation.
The Russian physiologist Ivan Pavlov laid the theoretical foundations of classical conditioning and associative learning with his famous experiments with dogs, in which dogs were taught to respond in a certain way by associating rewarding or punishing stimuli.
Humans and dogs can learn by association, that much is clear. But, that an actinia or sea anemone could do it seems, to say the least, strange. Associative learning has been observed in numerous animals, but until now it was considered the result of the existence of the brain, as a minimum requirement. Sea anemones are really simple animals in which there is no brain like that of higher species, but sometimes appearances are deceiving...
Pedro Martínez, ICREA researcher in the Department of Genetics at the University of Barcelona, and researchers from the University of Friborg (Switzerland) Gaelle Botton-Amiot and Simon G. Sprecher, have published (March 20, 2023) in the prestigious journal PNAS (Proceedings of the National Academy of Sciences) the results of a curious study in which, they say; "We tested the ability of the star sea anemone Nematostella vectensis to form associative memories using a classical conditioning approach".
The authors carried out laboratory experiments in which light was combined as a conditioned stimulus with an electric shock as an aversive unconditioned stimulus. "After repetitive training, the animals exhibited a conditioned response to light, indicating that they learned the association," indicate Botton-Amiot, Martínez, and Sprecher (in order of signature appearance in the original article).
The authors wondered if a brain was really necessary for associative learning and to put this condition to the test they recalled that creatures of the Cnidaria phylum, such as sea anemones, do not have brains. It is certain that they have a network of nerves but no known organs that process neural activity.
To find out if such creatures are capable of associative learning, the researchers chose to focus on sea anemones of the species Nematostella vectensis, which respond to light by moving their retractable, star-shaped tentacles to stimuli.
The research team collected several specimens and brought them to their lab for study. Each was subjected to a bright light and/or an electric shock. Some of the anemones were subjected to light and electric shock at the same time, while others received them regardless of time.
After several trials, the anemones that received the light and the shock at the same time learned to associate them as a single event and responded in the same way. This was demonstrated by turning on the light without applying the shock to see if the anemone would retract its tentacles anyway. The research team found that 72% of them did, showing that the creature was able to remember that shocks come with sudden bursts of light, and then responded as it normally would to a shock: moving its tentacles.
