21 May 2005

Trauma aside, we tend to think of our ability to store and retrieve memories as a good thing—but at what cost? In a brief article in today’s Science, Frederic Mery and Tadeusz Kawecki at the University of Fribourg, Switzerland, report that in fruit flies, at least, making long-term memories can reduce resistance to stress and accelerate the animal’s demise.

In Drosophila, as in humans, making long-term memory (LTM) means making protein, an expensive prospect energywise. To test for ramifications of that energy expenditure, Mery and Kawecki subjected flies to a Pavlovian-type conditioning regimen, then exposed them to extreme stress—the absence of food and water. They found that flies that had just laid down long-term memories were much less capable of dealing with the stressful environment, and died on average 4 hours (19 percent) earlier than control flies.

Fruit flies can also store what’s known as anesthesia-resistant memory (ARM), which differs from LTM in that protein synthesis is not required. The Pavlovian experiments, in which the flies were trained to associate a specific odor with a mild shock, were designed so that one or another form of memory would be laid down—LTM requires a rest interval between conditioning events so that the memory can be consolidated. Animals trained in the ARM protocol (no rest between conditioning events) lasted just as long in the stress test as control animals, indicating that it was the protein synthesis that sapped the strength of the flies trained in the LTM protocol.

The findings suggest that long-term memory comes at a price. The bigger question might be: What price are we humans paying for our memories?—Tom Fagan