Having a good memory can save your life, and smart creatures that learn to avoid bad situations (or home in on good ones) do better than animals that don't. However, life is unpredictable and it isn't always possible to base memories on established patterns. Divya Sitaraman and Troy Zars from University of Missouri, USA, explain that heat kills and Drosophila remember to avoid hot places better after random doses of heat. However, it wasn't clear whether it was the high temperature that enhanced the insect's memory or the unpredictable pattern. Sitaraman and Zars tested two groups of insects, one that had control over the thermostat and another that did not, to find out whether the high temperature or random temperature fluctuations primed the insect's memory (p. 4018).

First the team exposed one group of insects to a predictable pattern of high temperature fluctuations that the flies controlled by moving to one end of the arena, and a second group of insects to the same temperature fluctuations as the first, but with no control over the pattern, so that it occurred randomly as far as the insects were concerned. Having exposed both groups of insects to heat fluctuations, the team trained the insects to avoid one end of the arena by raising the temperature when the insects ventured there. Finally, the team tested the insects' memories by seeing whether they would remember to avoid the area that caused the temperature to rise, to see if the unpredictable pre-training heat pattern or just exposure to high temperatures had improved the insects' memories.

Amazingly, the memories of the flies that had experienced an unpredictable pre-training temperature pattern were twice as good as the flies that experienced a predictable pre-training temperature pattern: they were better at avoiding the end of the arena. So unpredictability enhanced memory formation in the flies. Sitaraman and Zars suspect that the flies store the unpredictable information in a ‘buffering system’. When the insects receive more accurate information about threatening temperatures the buffering system is released, improving the insects' memories.

Lack of prediction for high-temperature exposures enhances Drosophila place learning
J. Exp. Biol.