, a roundworm with just 300 neurons, that offers a simple laboratory model for studying how an animal learns.Physicists have developed a dynamic model of animal behavior that could shed light on the long-standing mysteries of associative learning, dating back to Pavlov’s famous canine experiments.
About 70 years later, psychologists built on Pavlov’s insights to develop the Rescorla-Wagner model of classical conditioning. This mathematical model describes conditioned associations by their time-dependent strength. That strength increases when the conditioned stimulus can be used by the animal to decrease the surprise in the arrival of the unconditioned response .
Pavlov discovered, however, that if he waited a while and then retested the dogs, they would once again salivate in response to the bell, even if no food was present. Neither Pavlov nor more recent associative-learning theories could accurately explain or mathematically model this spontaneous recovery of an extinguished association.C. elegans
The puzzle could not be resolved due to a major limitation of many of these experiments — the lengthy amount of time it takes for a worm to traverse a nine-centimeter petri dish in search of the preferred temperature.Nemenman and Ryu sought to overcome this limitation. They wanted to develop a practical way to precisely measure the dynamics of learning, or how learning changes over time.
Their experiments confirmed that if a worm is trained to associate food with a cooler temperature it will move to the cooler side of the droplet. Over time, however, with no food present, this memory preference seemingly decays.