By examining the brains of bees trained to different tasks, the researchers found that the number of connections between nerve cells may hold the answer to questions about individual cognitive differences. Bees with a greater density of nerve connections (known as synaptic complexes) in a specific part of their brains had better memories and learned faster than bees with fewer connections in these areas.
Li Li, lead author and PhD student at QMUL, said: “We wanted to determine what might make one individual bumblebee a better learner than another.”
She and her colleagues first trained bumblebees to discriminate between ten differently coloured artificial flowers, five of them containing rewarding sugar water and five of them containing bitter quinine solution. Two days later, the bees were tested on how well they remembered which colours were rewarding and which were not. Then, using an imaging technique called confocal microscopy, the researchers looked deep in the brains of these bees at areas known to be responsible for visual learning and memory.
They found that bees with a higher density of synaptic complexes within the visual association area of the brain had a better memory for the colours two days after training. Additional experiments showed that bees that learned faster (shown by taking fewer landings to find the right flowers) also had a higher density of synaptic complexes in the visual association area.
Clint Perry, senior author on the paper, said: “These correlations suggest that bees with more synaptic complexes in the visual association areas of their brain were predisposed to better memory and faster learning. Our findings are the first to suggest a strong correlation between the number of neural connections in the brain and how well an individual does on a cognitive task. However, at this stage we cannot show a causative link between the two.”
Impact of the environment
The researchers also found that the environment can affect the organisation of synaptic complexes in different ways. Bees trained with artificial flowers of many colours had greater densities of nerve connections than bees that trained among uncoloured or only a couple of coloured flowers.
Li Li said: “For the first time, we have shown that visual learning can increase the density of nerve connections in this area of the brain and that an enriched environment, where bees are exposed to many colours without learning anything from them, can also affect the synaptic organisation in the brain.”
The researchers hope their results will prompt further investigations into the potential link between the organisation of nerve connections and individual differences in learning and memory.
Dr Perry said: “Our results should provide new avenues for understanding the neural basis of cognition in all animals, including humans.”
Source: Queen Mary University of London