I just finished a book entitled Fly which is a history of the use of the fruit fly for biological research. The whole book was good, but one item I found particularly fascinating. One of the areas studied with the fly is learning and memory. A test device was created where the fly was kept in a test tube which allowed odors to pass through and to which an unpleasant electrical voltage could be applied. For a training session two odors were sequentially sent through the tube with odor 1 also receiving an electrical shock. The flies were then moved to a T junction where odor 1 was at the end of one leg and odor 2 was at the end of the other leg. With normal flies over 90% would walk toward odor 2 which had no adverse effect associated with it. With 1 training session the memory wore off with time and after 24 hrs. there was no evidence of learning. If the fly was exposed to 10 training cycles with 15 min between each session, they retained the memory at the end of a week.
The fact that such a simple animal could learn something and retain it over time was interesting, but what was really interesting was what happened when they created mutants with modified genomes. In one case they created a line of flies lacking one gene, which results in one missing protein out of 15,000, resulting in no short term learning. At the end of a training session it was equally likely to head toward odor 1 or 2. What was most interesting was the impact of another gene (CREB gene). When it was eliminated there could be short term learning, but no long term memory. No matter how many training sessions, at the end of 24 hrs there was no impact from the training. What was really neat was that when they inserted an additional copy of the gene the flies developed “photographic memory” and had a long term memory after just 1 training session. I found it fascinating that a change to the level of a single chemical (the protein created by the gene) could have such a profound impact on such complex behavior.