CHICAGO, May 24 (Xinhua) -- In a study of the fruit fly, researchers at the Northwestern University (NU) have identified a "thermometer" circuit of neurons that relays information about external cold temperature from the fly antenna to the higher brain, which may explain why it is hard for both flies and humans to wake up in the morning in winter.

In the study, the researchers developed new tools and used a combination of functional and anatomical studies, neurogenetic and behavioral monitoring approaches to conduct these experiments in both wild type and transgenic flies.

Having identified those neurons, the researchers followed them all the way to their targets within the brain, and found the main recipients of this information are a small group of brain neurons that are part of a larger network that controls rhythms of activity and sleep. When the cold circuit they discovered is active, the target cells, which normally are activated by morning light, are shut down.

Humans are creatures of comfort and are continually seeking ideal temperatures. Part of the reason humans seek optimal temperatures is that core and brain temperatures are intimately tied to the induction and maintenance of sleep. Seasonal changes in daylight and temperature are also tied to changes in sleep.

"Temperature sensing is one of the most fundamental sensory modalities," said Marco Gallio, associate professor of neurobiology at the NU's Weinberg College of Arts and Sciences. "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."

"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," said Michael H. Alpert, an NU postdoctoral fellow.

The study was published Thursday in the journal Current Biology. Enditem