Madison Cho

Hydras are freshwater organisms, ranging in size from ½ to 2 inches. They fall into a group known as Cnidaria, consisting of other organisms such as sea anemones, box jellyfish, and corals, all of which share many commonalities; in particular, they all have diffuse nerve nets, meaning their neurons are scattered across their bodies. Their simple nervous systems are ideal models for studying embodied cognition (cognitive activities outside the brain) and elucidating the origins of learning and cognition. Although multiple species of Hydra are known to exhibit basic responses to stimuli, no published studies have explored their capacity for associative learning—the process of forming a connection between two stimuli or between a stimulus and a consequence.

There have been studies on habituation—a decreased response to repeated stimuli—in the early 20th century, but their findings were inconclusive because the stimulus was not kept constant. However, since 1963, no studies have been conducted specifically on Hydra's learning processes due to the increased interest in the Drosophila and C. elegans models, which are more complex, reflect advanced behaviors, and have brains. Therefore, my study aims to determine whether Hydra vulgaris exhibits habituation and to explore the potential for associative learning, which has not yet been documented in published research. 

To accomplish this, I will administer a pulsing device and observe how the contraction probability of the Hydras changes over time. If the probability decreases by at least 70%, then this would indicate that these organisms can habituate. As for associative learning, I will use the same device and pair it with a stimulus that does not naturally induce any behavior to see if the Hydras can create connections between the two. Consequently, they would be able to contract to the stimulus they initially didn’t react to. My results will be significant because they would not only expand knowledge on this species but would also gain insight into how far back in the evolutionary tree these learning processes diverged, despite the shifted focus to other models.