We want to believe that we are completely different from fruit flies. But we actually share some serious similarities. In fact, aside from our mutual appreciation of berries and bananas, we both tend to get tired around mid-day—a tendency we can blame on our brains.
According to analysis in current biology, fruit flies often go to sleep around the middle of the day when temperatures are warmest. This, the authors say, is because the brain circuit that controls the fruit flies’ desire to sleep is connected to what is essentially a “brain thermometer” activated by heat.
The temperature drop
Temperatures affect all kinds of human and animal activity, but hot and cold weather seem to have a particularly strong hold on our sleep. “Changes in temperature have a strong effect on the behavior of both humans and animals and offer animals a cue […] to adapt to the changing seasons,” says Marco Gallio, professor of neurobiology at Northwestern University, in press release. “The effect of temperature on sleep can be quite extreme, with some animals choosing to sleep for an entire season—think of a winter bear—but the specific brain circuits that mediate the interaction between temperature and sleep centers remain largely unmapped.”
To better understand the connections between temperature and sleep in the brain, Gallio and team turned to Drosophila, also known as fruit flies. The team says these pests are suitable for studying sleep because they don’t disrupt sleep like other animals do. Instead, they listen to their instincts, which allows scientists to directly study the influence of external factors, such as temperature, on sleep.
Studying these flies in the lab, the team found that the brain pathway that controls their sleep is connected to a specialized system of receptors that act like a kind of thermometer, responding to temperatures around 77 degrees Fahrenheit or higher. This “brain thermometer” is activated in warm weather and stimulates sleep, providing an increase in the desire to sleep with the midday heat.
The team adds that this “brain thermometer” works together with another type of thermometer identified in previous documentwhich works in cold conditions.
“We identified a neuron that could be a site for integrating the effects of hot and cold temperatures on sleep and activity DrosophilaMichael Alpert, a neurobiology professor at Northwestern University and a member of the team, said in a press release. “This would be the start of interesting follow-up studies.”
Indeed, in addition to shedding light on the behavior of fruit flies, the team says these two thermometric systems could also improve understanding of the activities of a wide range of animals, including humans. “People may choose to take an afternoon nap on a hot day […] but what do you choose and what is programmed into you?” Gallio says in a press release. “In fact, there may be a very strong underlying biological mechanism that is being overlooked in humans.”