Classical conditioning of Hermissenda: origin of a new response.

Training of the marine snail Hermissenda crassicornis with paired light and rotation was previously shown to result in acquisition and retention of a behavioral change with many features characteristic of vertebrate associative learning. Here, this behavioral change is demonstrated to be classical, Pavlovian-like conditioning. A new response to light is formed (the CR) that is pairing-specific and resembles the unconditioned response (UCR) to rotation. The conditioned and unconditioned responses are relatively rapid, occurring within seconds of the onset of light or rotation stimuli, and correspond to pairing-specific reductions in speed during the same time period. Since the CR is independent of the presentation of rotation, and it is also expressed by the same effector system (the foot) responsible for the UCR, light stimulation has assumed some of the functional character of rotation.