• Phoebus Tian

Maybe it's not laziness that makes it hard to get out of bed in the winter

Updated: May 11, 2021

If you have trouble getting out of bed in the winter, don't blame yourself, check out the scientific explanation that neurobiologists have recently found in the brain.

To study how "sleep and wakefulness" are affected by outside temperature, scientists have used the model organism fruit fly. Professor Marco Gallio of Northwestern University has been studying how fruit flies sense temperature for a long time. His research team discovered for the first time that Drosophila has a class of nerve cells in its antennae that are responsible for reporting low temperatures outside. When the ambient temperature is below the fly's 'comfort zone' (25°C), these nerve cells remain active, sending a 'cold' signal to the brain. And the lower the temperature, the more intense the signal.

After identifying these neurons, the researchers traced them to the inside of the Drosophila brain using fluorescent labelling, two-photon calcium imaging, and a combination of anatomical and neurogenetic methods. The main recipients of cold information, they found, were a small group of neurons located in the control centre of the sleep-wake cycle.

Drosophila is regulated by the same biological clock as humans, with daily rest and activity occurring in 24-hour cycles. They also often rest during the night, and in the morning, they become more active as the light becomes bright and the neural networks that control the sleep-wake cycle promote wakefulness.

However, the researchers found that when the cold signal continued, the group of neurons in the brain that received the signal quickly became less active. As a result, the neural networks that promote wakefulness by light were suppressed. As a result, when the temperature dropped to a lower 18°C, the fruit flies were significantly less active in the morning - and it appears they slept in as well.

By studying the behaviour of fruit flies, the researchers note, we can better understand why temperature is crucial for sleep regulation. Although Drosophila are small thermoregulators and do not regulate their body temperature in the same way as humans, yet for humans, the temperature is just as closely linked to sleep maintenance, with seasonal changes in daylight and temperature also linked to changes in sleep.

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