Taiwanese scientists have made potential inroads in decoding how the human brain formulates long-term memories — by conducting experiments on the brains of fruit flies.
A research team led by Chiang Ann-shyn (江安世), a professor of life sciences and director of National Tsing Hua University’s Brain Research Center, reported the results of its seven-year study at the National Science Council yesterday.
The results were also published in an article in this month’s issue of Science.
“Neuroscientists have always wanted to understand how learning and memory are stored in the brain. Where does a new experience first occur in the brain? And how do these fresh experiences transform into stable long-term memories?” Chiang said.
Fruit flies and humans have many similar behavioral patterns, such as learning, memory, attention and environmental exploration, which are modulated by similar genes, Chiang said. However, the neural network of fruit flies, with about 100,000 neurons, is far less complicated than that of humans, which has about 100 billion neurons.
Chiang said previous research showed that long-term memory was dependent on the synthesis of new proteins in brain cells, so the team focused on finding in which cells long-term memories are formed.
Long-term memory depends on repetitive learning with intervals of rest, so the experiments were conducted by putting the fruit flies through repetitive training procedures, he said.
Using a new tool to visualize the synthesis of new proteins in living flies, the researchers — Chen Chun-chao (陳俊朝), Wu Jie-kai (吳介凱), Lin Hsuan-wen (林萱文) and others — repeatedly screened thousands of individual neurons and found that long-term memory was impaired after inhibiting protein synthesis in only two cell types — the dorsal-anterior-lateral (DAL) neurons.
The discovery has overthrown the previous belief that long-term memory is formed in the corpora pedunculata, or mushroom body, part of a fruit fly’s brain.
After doing the same screening work for between 10 and 12 hours a day over a period of about two years, Chen said they were at first surprised and uncertain about their findings and they repeated the experiments several times to ensure they were correct.
Chen said the team believed the entire neuron network of a fly’s brain could be mapped in about one or two years.
It is estimated that between 20 and 30 neurons function similarly to DAL neurons and this knowledge could be used to target similar neurons in the human brain in future research, Chiang said.
However, it still needs to be confirmed whether long-term memory is also formed via new protein synthesis in only a few nodes within the complicated circuit of the human brain, he said.