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How does your body know when to sleep and wake up? For a long time, scientists thought that your brain dictated your body’s internal clock. Now Australian and French researchers have found that the liver has a say, too.

Your body’s internal alarm clock is called your circadian rhythm and it helps you stay on a schedule that makes sense for your environment. For example, you feel sleepy when it’s dark out. To stay “set” to the right time, your circadian rhythm is influenced by daylight, temperature and even your habits. Scientists thought that all this coordination was done by the brain… until now.

Australian and French scientists, led by Dr Frédéric Gachon, have found that the liver helps to set our circadian rhythm. To show this, the scientists worked with mice, which are nocturnal animals. This means their natural circadian rhythm tells them to wake up when it’s dark. Next, Frédéric and his team transplanted human liver cells into the mice and watched what happened to their circadian rhythm.

“The mice in our study started to eat and be active before nighttime began, which is very unusual for a nocturnal animal,” says Frédéric.

The human cells changed the circadian rhythm in the mice to make them more active during the day, like us. The scientists only changed the liver cells in the mice so this experiment shows that the liver helps set the circadian rhythm. These findings have the exciting potential to help people with circadian rhythm disorders.