Research with trained pond snails has provided new evidence that flavonoids found in foodstuffs such as cocoa, green tea, and red wine really can boost memory. University of Calgary scientists showed that the flavonoid epicatechin found in dark chocolate improves and strengthens long-term memory in snails through a mechanism that appears to act directly on memory neurons.
Proving the hypothesis that chocolate in some way boosts brain functions such as memory isn’t easy because human and other vertebrate research is set against a background of huge numbers of other external influences that affect how we remember, and for how long. To try and overcome this, the University of Calgary’s Lee Fruson, Ken Lukowiak, Ph.D., and Sarah Dalesman, Ph.D., turned to the pond snail Lymnaea stagnalis, an invertebrate that can be trained to carry out simple functions in response to simple cues.
In this case it was a matter of how they breathe. Pond snails normally take in oxygen from water through their skins, but when placed in deoxygenated water the animals extend their breathing tubes above the water surface and open them to take in oxygen via the air. The Calgary team trained snails to keep their breathing tubes closed in deoxygenated water, in response to a tap on the tube itself. The training process takes about half an hour, and normally the snails would remember what to do in response to this cue for up to about three hours, but no longer.
To see how epicatechin might affect this "memory", the investigators added a small dose of the chemical into the snails’ pond water and then a day later moved the animals to deoxygenated water and gave them two training sessions. Incredibly, they found that the animals "remembered" what to do in response to a breathing tube tap for up to several days, rather than just for a few hours. Importantly, the concentration of epicatechin added to the water wasn’t enough to affect other aspects of the snails’ behavior. “We have to make sure that we’re not looking at wired animals,” Dr. Lukowiak points out.
The epicatechin also appeared to strengthen the memory. When the snails' trainers tried to extinguish the "keep tube closed" memory with one where the animals instead opened their breathing tubes, the epicatechin-boosted snails refused to learn the new process, and instead kept their breathing tubes shut. The memory cemented in their neural circuitry by epicatechin couldn’t be extinguished.
Of particular interest was the finding that the mechanism by which epicatechin acts on memory doesn’t rely on sensory cues, such as, for example, memories of predators that are triggered by smell, and rely on a serotonergic (5-HT) signaling pathway. Rather, the epicatechin may act directly on the neurons that store memory.