Hot Weather Is Linked to Sleepiness in Fruit Flies, Too

If you felt sleepier than usual during the heat wave, you are not the only one. A connection between temperature and sleep can be found in nonhuman species as well. A study conducted by neurobiologists at Northwestern University sheds light on the biological basis for why hot temperatures can induce feelings of tiredness and the inclination to take naps in the middle of the day. Here's a breakdown of major findings:

Biological Determination in Fruit Flies: The study reveals that fruit flies exhibit a pre-programmed behavior to rest during a hot afternoon. This behavior is linked to the presence of "absolute heat receptors" near the base of their antenna that connect to nerve cells in their brains. The researchers had previously found receptors for cold.

Heat Receptors: Researchers found that the heat receptors become activated when temperatures rise above a comfortable 77 degrees Fahrenheit. The study suggests that there is a direct neural response to heat that influences the flies' behavior.

Implications for Humans: While the study focuses on fruit flies, it raises intriguing questions about potential parallels in human biology. The findings imply that humans may also have underlying biological mechanisms that respond to external temperatures, influencing our sleep patterns and energy levels.

Cultural and Biological Factors: A co-author of this study, Marco Gallio, highlights that while cultural norms (think of siestas) may influence human behavior regarding naps, there could be strong biological underpinnings as well. The study suggests that similar biological circuits might exist in humans, though further research is needed to elucidate them.

The daily or diurnal cycle of wakefulness, sleep, and hormones in humans is centered on the SCN (suprachiasmatic nucleus), a cluster of nerve cells near the center of the brain, and temperature might be another input to this structure, along with signals that respond to light.

For the fruit fly, sleepiness in hot weather is only one of the intriguing behaviors of these tiny insects. They can get drunk on alcohol—at least it causes them to lose their grip on a test tube wall. Their response to anti-anxiety and antidepressant drugs is being investigated. Their behavior is being imitated by AI (artificial intelligence) systems trained by observing the behaviors of real fruit flies, like walking, flying, and grooming.

In summary, the study underscores the role of temperature-sensitive neural circuits in regulating rest and activity patterns in fruit flies, hinting at possible analogous mechanisms in humans. Imitating the behavior of these tiny insects by artificial intelligence, and the effects of common drugs used by humans, provide a foundation for future research into the intersection of environmental influences and circadian rhythms in both flies and potentially in humans.