On the hottest days of summer, we may find ourselves sleepy in the middle of the day. In some parts of the world, it is a cultural norm to take short naps and close businesses during the hottest part of the day. It turns out that biology, not just culture, may be behind this.
Temperature affects the duration of human behavior, from feeding and activity levels to sleep-wake cycles. We may find it more difficult to sleep at night in the summer and may be slow to get out of bed on cooler mornings. But the link between sensory neurons and the neurons that control this cycle is not fully understood.
Neurobiologists at Northwestern University have found some clues as to what’s going on. In a new study, researchers found that fruit flies are preprogrammed to take a nap in the middle of the day. These insects are a particularly good model for studying big questions like “why do we sleep?” and “what does sleep do for the brain?”, since they are not trying to alter instinct in the same way that humans do.
Naps are longer in summer
The researchers discovered that the brain neurons that receive information about heat are part of the larger system that regulates sleep. When the hot circuit, which runs parallel to the cold circuit, is active, the cells that promote midday sleep stay on longer. This results in an increase in midday sleep that keeps flies away from the hottest part of the day.
The study was made possible by a 10-year initiative that produced the first complete map of neural connections in an animal (a fly), called a connectome . With the connectome, the researchers have access to a computer system that tells them all the possible brain connections for each of the fly’s 100,000 brain cells. Even with this detailed roadmap, however, researchers still need to figure out how information in the brain gets from point A to point B.
The different circuits for hot and cold temperatures make sense because temperatures can have quite different effects on physiology and behavior. This separation may also reflect evolutionary processes based on the Earth’s hot and cold cycles.
could be biological
Next, the team of researchers hope to discover the common goals of the hot and cold circuit, to discover how each may influence naps.
They have identified a neuron that could be an integration site for the effects of hot and cold temperatures on sleep and activity in flies. This would be the beginning of interesting follow-up studies. The team is interested in looking at the long-term effects of temperature on behavior and physiology to understand the impact of global warming, looking at how adaptive species are to change.
People may opt for afternoon naps on a hot day, and in some parts of the world this is a cultural norm, but what do you choose and what is programmed into you? Of course, it’s not cultured in flies, so there might actually be a very strong underlying biological mechanism that is overlooked in humans.