*** Appendix - Associative learning in Drosophila melanogaster - a summary of research findings by Brembs (2000)

In Brembs' experiments (2000), it turned out that classical conditioning was much less effective than operant training. Heisenberg, Wolf and Brembs (2001, p. 4) suggest that in classical training, the fly may have been distracted by searching for a behaviour that could control the temperature.

In Brembs' experiments (2000), the flies, despite having two forms of feedback, did not learn to restrict their yaw torque range significantly faster in sw-mode than in operant learning (yaw torque mode, where only B -> US associations could be formed). Brembs (2000, p. 26) attributed this negative result to the "artificiality" of the sw-mode set-up. (On the other hand, Heisenberg, Wolf and Brembs (2001, p. 5) found that sw-mode learning was more efficient than operant learning.)

Flies performed much better in fs-mode than in classical conditioning, where they were powerless to control their circumstances. "As expected, the more natural complex learning tasks are easier to solve than the more artificial single-association tasks" (Brembs, 2000, p. 30).

Generally, flies learned best in natural situations involving complex associations than in artificial set-ups with single-association tasks (pure operant conditioning or classical conditioning).

Classical conditioning and operant conditioning were shown to be independent learning processes.

It was also demonstrated that operant conditioning could assist (or boost) learning via classical conditioning, and that classical associations could be formed during operant training.

Flies were able to transfer colour or pattern preferences acquired during one mode of training (sw-mode) to another mode of learning (fs-mode).

It was shown that flies could remember patterns without heat reinforcement and compare them to other patterns later.

Additionally, the flies' ability to learn compound stimuli was investigated by using both colors and patterns as visual cues. It was shown for the first time that Drosophila could learn compound stimuli and recall the individual components independently and in similar proportions (Brembs, 2000, p. 31). Interestingly, it was discovered that "flies acquire, store and retrieve the two CSs 'colors' and 'patterns orientations' separately. They do not store them only as a compound" (Brembs, 2000, p. 30).