> [A] lot of species, including anemones, corals, and jellyfish ... have a fairly diffuse nerve net and lack anything that's clearly brain-like. ... [A]pparently, that's enough to perform associative learning [... - t]hrough repetition, an animal learns to associate an event with something that's otherwise unrelated to that event

> Cnidaria ... - everything from the tiny hydra to enormous jellyfish - have a diffuse web of neurons called a nerve net [...] clearly capable of performing some of the functions we normally associate with a brain

> [Researchers ...] combined exposure to light with ... an electric shock [in anemones. ... The result] isn't the sort of conditioning seen with Pavlov's dogs, where the animal learns an association in a way that allows it to respond to an unrelated cue. Instead, the animals here learned to interpret the two stimuli as a single trigger, and so started needing both to respond. // All of this indicates that there must be some form of central coordination within the nerve net that allows the animal to integrate environmental signals and trigger a response that involves most of the organism. Many cnidarians have sections of the nerve net with higher concentrations of neurons, but these don't seem to have been associated with any specific functions. So, it's not clear whether this memory and coordination is associated with any sort of physical structure. // It's possible to interpret these results in light of recent results showing that disorganized neurons in a culture dish could "learn" to play Pong. This was interpreted as an indication that neurons natively develop expectations for the inputs they will receive and adjust their behavior when those inputs don't match. That behavior could produce an associative memory without requiring any central organization. It also would suggest that the nerve net should be able to easily unlearn the association if the two triggers stop being linked - something that would be very easy to test

Original research article: Associative learning in the cnidarian Nematostella vectensis - http://dx.doi.org/10.1073/pnas.2220685120

> The ability to learn and form memories allows animals to adapt their behavior based on previous experiences. Associative learning, the process through which organisms learn about the relationship between two distinct events, has been extensively studied in various animal taxa. However, the existence of associative learning, prior to the emergence of centralized nervous systems in bilaterian animals, remains unclear. Cnidarians such as sea anemones or jellyfish possess a nerve net, which lacks centralization. As the sister group to bilaterians, they are particularly well suited for studying the evolution of nervous system functions. Here, we probe the capacity of the starlet sea anemone Nematostella vectensis to form associative memories by using a classical conditioning approach. We developed a protocol combining light as the conditioned stimulus with an electric shock as the aversive unconditioned stimulus. After repetitive training, animals exhibited a conditioned response to light alone - indicating that they learned the association. In contrast, all control conditions did not form associative memories. Besides shedding light on an aspect of cnidarian behavior, these results root associative learning before the emergence of NS centralization in the metazoan lineage and raise fundamental questions about the origin and evolution of cognition in brainless animals