This separation may also reflect evolutionary processes based on heat and cold cycles of the Earth. The different circuits for hot versus cold temperatures make sense to Gallio because "hot and cold temperatures can have quite different effects on physiology and behavior," he said. However, even with this extremely detailed road map, researchers still need to figure out how information in the brain goes from point A to B. With the connectome, researchers have access to a computer system that tells them all possible brain connections for each of the fly's ~100,000 brain cells. The study was enabled by a 10-year initiative that produced the first completed map of neural connections in an animal (a fly), called the connectome. This results in an increase in midday sleep that keeps flies away from the hottest part of the day. When the hot circuit, which runs parallel to the cold circuit, is active, the target cells that promote midday sleep stay on longer. Just as they expected based on the results of their previous paper on cold temperature, researchers found that brain neurons receiving information about heat are part of the broader system that regulates sleep. Not surprisingly, its favorite temperature also matches that of many humans. As it turns out, the common laboratory fruit fly (Drosophila) has colonized nearly the entire planet by forming a close association with humans. The paper is the first to identify "absolute heat" receptors in fly head, which respond to temperatures above about 77 degrees Fahrenheit - the fly's favorite temperature. They also allow researchers to study the influence of external cues like light and temperature on cellular pathways. Gallio led the study and said fruit flies are a particularly good model to study big questions like "why do we sleep," and "what does sleep do for the brain" because they don't attempt to disrupt instinct in the same way humans do when we pull all-nighters, for example. "The effect of temperature on sleep can be quite extreme, with some animals deciding to sleep off an entire season - think of a hibernating bear - but the specific brain circuits that mediate the interaction between temperature and sleep centers remain largely unmapped." "Changes in temperature have a strong effect on behavior in both humans and animals, and offer animals a cue that is time to adapt to the changing seasons," said Marco Gallio, associate professor of neurobiology in the Weinberg College of Arts and Sciences. A follow-up to their 2020 Biology paper that identified a brain thermometer only active in cold weather, the new paper explores a similar "thermometer" circuit for hot temperatures. 17) in the journal Current Biology, researchers found that fruit flies are pre-programmed to take a nap in the middle of the day.
Northwestern University neurobiologists have found a few clues about what's happening. But the link between sensory neurons and neurons that control this cycle are not understood completely. We may have a harder time sleeping in the summer and be slow to get out of bed on colder mornings.
Temperature affects the span of human behavior, from eating and activity levels to sleep-wake cycles.
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