CLASSICAL-CONDITIONING, DIFFERENTIAL CONDITIONING, AND 2ND-ORDER CONDITIONING OF THE APLYSIA GILL-WITHDRAWAL REFLEX IN A SIMPLIFIED MANTLE ORGAN PREPARATION

Nonassociative learning was previously examined in a simplified prepar ation consisting of the isolated mantle organs and abdominal ganglion of Aplysia californica that is advantageous for relating cellular even ts to behavior (T. E. Cohen, S. W. Kaplan, E. R. Kandel, & R. D. Hawki ns, 1997). Results of the current study show that the gill-withdrawal reflex in that preparation also underwent 2 associative forms of learn ing: classical conditioning and differential conditioning. In addition , the reflex underwent second-order conditioning with either forward o r simultaneous pairing of a novel conditioned stimulus (CS2) and a pre viously conditioned stimulus (CS1). Moreover, extinction of CS1 after simultaneous second-order conditioning was accompanied by a decrease i n responding to CS2, suggesting that the conditioning might have invol ved formation of an association between the CSs. In each of these para digms, learning in the Aplysia mantle organ preparation resembled lear ning in vertebrates.