How does a tiny brain determine how fast it learns? A new study on honey bees shows that learning speed depends on a delicate balance between two brain chemicals.
Even before a bee receives a reward, its brain activity can predict how quickly a bee will learn. A research team led by Virginia Tech’s Fralin Biomedical Research Institute made the discovery.
Why bees must learn quickly
The lifespan of worker bees is only a few weeks. During that short time, they must find flowers, collect nectar, and return safely to the nest. The location of flowers and the amount of nectar change frequently. Survival depends on knowing which smells lead to food.
“Bees are not born into this world knowing what they need to know in order to find flowers or harvest nectar or pollen,” said Brian A. Smith of Arizona State University.
Foragers travel over many miles of land. “This is a huge area for an animal with a small brain,” Smith added.
Learning must remain flexible. “That bee must be a learning machine,” Smith said. “They must be willing to forget what they learned yesterday and learn something new today. Otherwise they will never be able to carry out their mission within the colony.”
Brain chemicals behind learning
The researchers focused on four neurotransmitters: dopamine, serotonin, octopamine, and tyramine.
Octopamine and tyramine play central roles in insect behavior. Tyramine is converted to octopamine in nerve cells, and often both work in opposite ways.
Previous studies have shown that octopamine may function as a reward signal during learning. Tyramine often causes opposing effects in certain behaviors.
In other insects, the balance of both chemicals influences feeding, locomotion, and even attraction and avoidance responses.
Scientists have discovered that in honey bees, differences in octopamine and tyramine levels act like chemical signatures. Strong initial differences predicted faster learning. Weak or delayed differences predicted slower learning.
Measuring small signals
To study these small changes, the researchers placed very thin carbon fiber electrodes inside the bees’ brains. The electrodes targeted an area that processes smells called the antennal lobe.
Using a machine learning model, the team measured chemical changes many times per second.
“We didn’t even have a way to measure monoamines and the bee brain,” says study co-author Pendleton R. Montague.
“Now we’ve done this work in humans and turned it back into tiny electrodes that we can insert into the bee’s brain while the bee is learning and conditioning.”
A deep learning model was trained using known chemical mixtures. After training, the system can estimate dopamine, serotonin, octopamine, and tyramine levels in real time while learning.
Test how bees learn
Laboratory tests showed that the bees smelled an odor called hexanol. After about a second, the sugar water touched the antenna.
After several pairings, the bees learned to extend the feeding tube when the odor appeared alone. Scientists call this behavior the proboscis extension response.
Some bees learned the odor-sugar combination after just three attempts. Others needed up to eight. Some showed no learning during the 12 trials.
Before sugar was introduced, researchers exposed bees to scent alone. At that early stage, chemical patterns were already predicting future learning rates.
The bees that emitted the octopamine minus tyramine signal stronger and earlier learned later and more quickly.
Dopamine and serotonin did not show the same predictive pattern. Over repeated training sessions, dopamine and serotonin levels gradually decreased in both learners and non-learners.
In contrast, octopamine and tyramine were altered in a more complex manner.
Signals that shape learning styles
Scientists describe octopamine and tyramine as an opposing pair. One goes up while the other goes down, creating a difference signal. The timing and strength of that difference reflected how quickly bees form coalitions.
After the bees learned the odor-reward link, the direction of the chemical pattern changed. This may help limit further learning once the task has been mastered. This mechanism prevents overlearning and may help bees regulate their attention.
Mathematical analysis reveals that one major pattern hidden in the chemical data is strongly related to learning speed. The pattern mainly reflected the activity of octopamine and tyramine.
Why Differences Help Colonize
It is not necessarily beneficial for the hive that all bees learn at the same rate. Quick learners may quickly take advantage of known flower sources.
Slow learners may respond better to long-term changes in their environment. Genetic differences among workers can influence learning styles and foraging roles.
“Bees have a sophisticated system for pursuing this,” Montague says. “They can game the system to make prudent or risky choices.”
What does this mean for humans?
Octopamine and tyramine belong to an ancient chemical system that evolved over 130 million years ago. Similar systems still influence human attention and learning.
“These are evolutionarily very old systems that are still present in our brains,” Montague said. “We can condition bees to stimuli in the world that are associated with humans.”
“From a biomedical perspective, understanding neural networks gives us some insight into how the larger brain works,” Smith says.
By studying brains smaller than a grain of rice, scientists have gained new insight into how learning begins.
A simple chemical balance inside the bee determines whether new information takes hold quickly or slowly. This small balance may contain learning cues for many species, including humans.
The research will be published in a journal Science progresses.
—–
Like what you read? Subscribe to our newsletter for fascinating articles, exclusive content and the latest updates.
Check out EarthSnap, a free app from Eric Ralls and Earth.com.
—–
