Einstein Science Reporting for Kids
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American Association for the Advancement of Science

Why sleep? Flies tell us why

Isolated flies do not have much interaction, so do not need much sleep. The flies sharing a bigger space have more interaction and need more sleep.
Cartoon credit Justin Yun.

Sleep is a mystery. Scientists do not know why we need sleep. But, adults know they need sleep and parents know children need sleep. Other living beings need sleep. But why? Resting restores our body, so rest should be enough.

Scientists hypothesize -- that is, they suggest a solution based on what they know and follow up this hypothesis with experiments -- that our bodies require sleep so our brain can process what we have learned during the day.

Scientist Dr. Indrani Ganguly-Fitzgerald used fruit flies in a series of experiments. She learned that when flies used their brains, they needed more sleep. It starts when flies are very young they need a lot of sleep like babies and the need to sleep continues as the flies get older.

In her experiment, she kept some young flies in a tube by themselves. They did not sleep much. Some other young flies were put together with older flies in a big jar and they needed a lot of sleep because they had been taking in information from the other flies.

Tests with older flies showed that they needed sleep to, for their brains to process the information they learned during the day.

She wanted to know more so she watched flies that were taught a lesson. Afterward the flies slept a lot. Later they did well when they had a test. Some flies were not allowed to sleep much, and they made mistakes on their tests.

As a geneticist, someone who studies genes and how they work in living things, Dr. Ganguly-Fitzgerald wanted to understand what happens in our bodies. "I tested the flies we studied and they all had genes involved in memory and information processing in the brain," she said. "I looked at some flies called dunces and they did not have these genes."

Understanding how sleep works with memory allows researchers to understand diseases in humans and to experiment until they can find medicine or cures for people with memory diseases like Alzheimer's disease and depression.

Dr. Ganguly-Fitzgerald's work show to other scientists that flies can be a good method of studying the connection between sleep and memory. "Of all genes known to cause human diseases," she explains, "more than 60 percent are found in the fruit fly."

Special advice from Dr. Ganguly-Fitzgerald: "For kids, from parents: Sleep now, Play better later. For parents: Let kids play now, they will sleep better later."