Scent-sational source of memory clues

Bees are more sophisticated than you think. Already proving inspirational for automated robotics, now they are going some way to helping us better understand memory.

The parts of the brain responsible for memory have long remained intriguing and undiscovered, but ANU scientists have taken a fresh step in unravelling the secret.

Scientists have found that honeybees, Apis mellifera, can be trained by scent to recall and fly to a specific nectar location — a finding with potentially significant implications for understanding memory, memory degeneration and associative recall in humans.

Dr Judith Reinhard, Professor Mandyam Srinivasan and Dr Shao Wu Zhang, from the Visual Sciences Group in the ANU Research School of Biological Sciences, have advanced historical theories of the honeybee’s sophisticated sense of smell in their paper Scent-triggered navigation in honeybees, published in Nature.

Past research has indicated that the nectar scent on a forager bee returning to the hive could induce other experienced nectar-collecting bees to revisit the source without having to use another communication form widely-used by bees, known as the ‘waggle’ dance.

As part of their research, the ANU team marked individual bees and trained them to visit two differently scented sugar feeders each placed 50 metres from their hive (pictured). Feeder One was scented with rose, while Feeder Two was scented with lemon. The two feeders were separated by 50 metres.

After two days of training, the rose and lemon scented feeders were replaced with two empty, unscented ones. This was important so that the researchers could ensure the bees were not just homing in on the familiar scent, or going back to the hive and doing the waggle dance (indicating a rich source of nectar), causing other worker bees to fly to the hive.

With a small fan, the team first blew rose scent into the hive for eight minutesand recorded how many trained bees responded by flying to the position of the rose-scented feeder. They then repeated the experiment with lemon scent, counting the number of bees that flew to the position of the lemon-infused feeder.

The researchers observed how many bees flew to the spot of the appropriate feeder first, how many circlings of the feeder the bees made and how many landed on the feeder. The experiment was repeated four times and total visits were then compiled.

The injection of rose scent into the hive caused the trained bees to fly predominately to Feeder One (69.8 per cent), while the injection of lemon scent caused the majority (72.6 per cent) of trained bees to visit the site of Feeder Two — despite the fact that both feeders were empty and unscented.

“The trained bees that emerged from the hive upon injection of a scent showed a significant preference for the location that had carried the scent during training,” the researchers found.

“Thus, a familiar nectar scent, encountered at the hive, can trigger specific route memories that expedite navigation to the food source.”

Over the next two weeks, the researchers repeated the test with newly-trained bees on different pairs of scents (rose and almond and lemon and almond), with similar results.

“Our findings reveal that associative recall is an important mechanism that honeybees could use, in addition to the dance language, to navigate successfully and repeatedly to an attractive food source,” the research team concluded.

“The taste and scent of nectar samples distributed by foragers on return to the hive could trigger recall of specific visual and route memories associated with the food site in experienced recruits.

“Recalled items could be the distance and direction of the food source, the landmarks expected en route and at the destination, and the flower’s shape and colour.

“Such precise recall should expedite flight to the food site, thus enhancing the foraging efficiency of the colony.”

The team believes this research shows great parallels to associative recall and memory in humans.

“Human senses, like the honeybee’s, are intricately connected. When we smell something familiar, such as a freshly baked cake, we can almost instantly recall what it looks and tastes like, and vice-versa,”Dr Reinhard said.

“Another application could extend to students burning incense whilst studying for an exam, then dabbing on the same incense whilst writing it, to facilitate recall of important facts,” Professor Srinivasan suggested.

“Honeybees are a great model to study learning and memory,” Dr Reinhard said.

“With the honeybee genome near completion, we now have a chance to discover the molecules involved in memory. We hope this could then help us better understand associative recall and memory in humans.”

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