"Seriously, it doesn't matter how many times you ask me. I'm never going to remember where he said he was going. I don't even know why you're still here.''
"I just don’t believe you.”
"Have you looked in his house yet? That'd be the first place I'd look. Under his bed or something, I don't know."
"Would a Toblerone help jog your--"
"HE'S UNDER MY BED. And now I remember where I left my ninth-grade por-- oh dear."
Flavonoids are the chemical compounds that give plants their colours, flavours and scents, and have been linked to many health benefits in humans, including antiviral, anti-inflammatory and antioxidant effects. Previous studies have also linked flavonoids to some improvements in the cognitive function of rodents, which has led scientists to suggest that the same could be true for humans, but due to difficulties in studying the way our memory is influenced, we know very little about how this could work.
This week in The Journal of Experimental Biology, a team of scientists from the the Hotchkiss Brain Institute at the University of Calgary in Canada reported on the effects of a particular type of flavonoid called Epicatechin (epl) on the long-term memory formation of the great pond snail (Lymnaea stagnalis). Epl is of particular interest to us, because it can be found in a number of common foods such as cocoa, green tea, red wine and blueberries.
According to the researchers, the snail represents the ideal study subject, because while human memories are influenced by many external factors, the snail's experience can be easily regulated, so the effects of epl can be more reliably isolated. The snail also has relatively large neurons, making it possible to find the exact point in the brain at which memory is formed, and its neural signalling properties are observable while the animal is still alive, allowing the researchers to see the effects of epl on behaviour in vivo for the first time.
In 2010, the researchers presented the results of a study at the Society for Experimental Biology Annual Conference in Prague in which they were able to train great pond snails to memorise a particular behaviour related to breathing. Great pond snails are bimodal breathers, so when in water that is highly oxygenated, they can breathe by absorbing oxygen directly through their skin. And when oxygen levels in the water drop, they can open a respiratory orifice called the pneumostome above the surface of the water to take in air that will be processed by a very basic lung.
In their experiment, the team would artificially reduce the amount of oxygen in the snails' water, prompting them to open their pneumostome above the surface to breathe. Here they would receive a gentle poke with a wooden stick, which aggitated them enough to make them shut their pneumostome. This process was repeated over a two-hour training period, and the snails were shown to remember the pokes a full day later by reducing the number of times they came up for air. The researchers classified this as the formation of a long-term memory.
In their most recent experiment, the researchers, led by undergraduate student Lee Fruson, trained the snails for a half-hour period to find that the most they could manage was a memory that lasted less than three hours, which was classified as an intermediate memory. They then gave the snails a dosage of epl, and found that after just half an hour of training, the snails remembered to keep their pneumostomes shut in deoxygenated water up to three days (72 hours) later – a huge improvement on both the persistence of the memory and the training time.
Next, the team wanted to see how strong these new long-term memories were, for example, how difficult it would be to replace them with a new memory. By not poking the snails when they came up to breathe, the scientists could observe if the original memory would be replaced by a new memory, and they found that despite the absence of pokes, the snails kept their pneumostomes shut, proving that this long-term memory was persistent over a long period of time, and not easily forgotten.
Exactly how epl enhances memory is not understood, but the researchers say that one theory based on observations in mammals suggests that flavonoids act as antioxidants, which protect neurons from injury due to oxidative stress. Another factor is that flavonoids derived from cocoa have been shown to increase blood flow to the central nervous system, which has been linked to neurogenesis and memory enhancement. The team now wants to look more directly at how epi affects the snails’ memory neurons, and if it can affect memories related to feeding.