Associative learning of visual and vestibular stimuli in Lymnaea

A conditioned withdrawal response was characterized in the pond snail Lymnaea stagnalis. Using light as the conditioned stimulus and high-speed orbital rotation as the unconditioned stimulus, experimental animals were trained with 30 paired presentations of light and orbital rotation per day for 3 days. After training, all experimental animals responded to light with a withdrawal response, the conditioned response. Control animals exposed to the same number of explicitly unpaired presentations of light and orbital rotation, light alone, or no stimulation did not respond to light. Thirty paired presentations per day for 2 days produced less than optimal acquisition of the conditioned withdrawal response. Neither 45 paired presentations per day for 2 days nor 90 paired presentations for 1 day resulted in complete acquisition of the conditioned withdrawal response. The conditioned withdrawal response observed following 30 paired presentations per day for 3 to 5 days persisted to Day 10, regardless of the number of training days. As a measure of savings, reacquisition of the conditioned response after extinction was investigated. After the conditioned withdrawal response was extinguished, only 2 to 5 paired presentations of light and orbital rotation were required for reacquisition of the conditioned response for most animals. This study further establishes Lymnaea as an animal model of basic associative learning.