EVANSTON, Ill. — When it’s cold outside, getting out of bed can be a very uncomfortable process. Weather can affect the behavior and mood of my many living beings. A team of Northwestern University neurobiologists is looking at how sensory and sleep cycle neurons react to these chillier temperatures. Their study on fruit flies, has found a thermometer circuit can transfer information about cold temps from their antennas right to the brain.
For humans, the team believes this circuit may explain why seasonally cold and dark conditions hinders the brain’s ability to wake up and be active.
“This helps explains why — for both flies and humans — it is so hard to wake up in the morning in winter,” study lead Marco Gallio says in a university release. “By studying behaviors in a fruit fly, we can better understand how and why temperature is so critical to regulating sleep.”
Staying comfy in the cold
The study authors are one of only groups in the world that is systematically studying temperature sensing in fruit flies. Researchers say the comfort zone of a fly is 77 degrees Fahrenheit. “Absolute cold” receptors live in the fly’s antenna and it only responds to levels lower than the comfort zone.
Fruit flies and humans differ when it comes to preferred environmental temperatures. Humans need comfort and brain temperatures are closely linked to the science behind sleep. As the seasons change, the human mind adapts for optimal comfort.
“Temperature sensing is one of the most fundamental sensory modalities,” Gallio adds. “The principles we are finding in the fly brain — the logic and organization — may be the same all the way to humans. Whether fly or human, the sensory systems have to solve the same problems, so they often do it in the same ways.”
Waking up is hard to do
Rhythms of activity and sleep are controlled by a bigger network, including a group of brain neurons. The target cells, that are normally activated by morning lights, are shut down by the brain neurons when they discover the active motion of cold circuits.
“The ramifications of impaired sleep are numerous — fatigue, reduced concentration, poor learning and alteration of a myriad of health parameters — yet we still do not fully understand how sleep is produced and regulated within the brain and how changes in external conditions may impact sleep drive and quality,” co-author Michael H. Alpert explains.
The classic model system known as Drosophila (for circadian biology), helped researchers study the mechanisms that control our 24-hour cycle of both rest and activity. Researchers applied their focus to the external influence of light and temperature — how they both affect activity and sleep.
“It is crucial to study the brain in action,” researcher Dominic D. Frank adds. “Our findings demonstrate the importance of functional studies for understanding how the brain governs behavior.”
The study is published in the journal Current Biology.