Even a sleeping fly senses danger

The buzzard becomes apparent in an emergency because its brain allows strong sensory stimuli to filter through the sleep state, according to German researchers who measured the brain activity of banana flies.

While sleeping the brain electrical activity of both humans and flies pulses with slow waves lasting about a second.

During such times, the researchers saw the banana flies resting, pacing leisurely or absentmindedly swatting themselves. External stimuli did not trigger sleep apnea, as long as they were muted.

Sleeping in the brain, the areas that emphasize and suppress stimuli pulse their slow waves in unison, researchers say Nature-in the scientific journal.

The neural networks that suppress activity and nurture sleep dominate in simultaneous pulsation.

But a strong enough external stimulus can overcome the neural networks that support rest, causing the noise filter to fail and the fly to wake up.

This forms a filter for the message attempts of the senses. The sieve becomes tightest when the flies are sleepy and their rhythm is at rest.

For safety reasons, however, the noise filter remains leaky so that, for example, a strong light or a gust of air wakes you up.

Published in Science in Nature 3/2026