If you’ve ever forgotten your morning cup of coffee and noticed yourself dozing off in the middle of the day, you might have experienced microsleep, a brief but very deep episode of drowsiness. Microsleep and regular sleep affect our bodies in similar ways, including changing our brain activity and decreasing how much attention we pay to our surroundings. Because we don’t consciously choose to microsleep like we choose to go to bed, the potential of having a microsleep episode can be dangerous in certain situations, such as while driving.

During regular sleep our brain still respond to sounds. Research published in the Journal of Neurophysiology (JNP) suggests that our brain might also be able to respond to sounds during microsleep. To test this, a group of young adults stared at a screen and listened to a variety of noises while lying in a functional magnetic resonance imaging (fMRI) machine. This type of machine measures fluctuations in brain activity by detecting changes in blood flow. The participants listened to white noise that varied in either volume (loudness) or pitch (tone)—when people are awake, their brain responds reliably to changes in these features. The experiment was held in the afternoon when many people feel a little drowsy and may tend to microsleep.

The researchers found that brain activity increased in response to noises during microsleep. What was surprising was that when the participants were awake, there was a different pattern of brain activity depending on whether they heard a high- or low-pitched noise. However, this difference in brain activity was not found during microsleep. This suggests that we process information relating to sound and hearing differently during microsleep than when we’re awake.

When you think about the times you catch yourself dozing off, this decrease in information processing makes sense. So, sleep in an extra 15 minutes or drink that extra cup of coffee. Otherwise, your brain might miss a change in pitch.