Hulton Archive via Getty Images Parts of the brain go "offline" even when we're awake, researchers find.

Being awake doesn’t mean that your brain is fully woken up.

Small clusters of neurons constantly cycle between being “on” and “offline” ― as if they are continually falling asleep and waking up, according to new research.

Stanford neuroscientists found that the same cycles of oscillating brain activity that occur while we’re asleep also take place during a waking state, albeit on a smaller scale.

While the activity of the entire brain ebbs and flows in waves during sleep, it seems that tiny areas of the brain independently “fall asleep” and “wake up” while we’re awake, too. During sleep, these cycles are easy to detect because they occur across the brain. But during a waking state, the cycles occur only in seconds or fractions of a second, and they take place in small, localized regions across the brain.

The results of the study, which were published Dec. 1 in the journal Science, also showed that neurons spend more time in their active, or “on,” state when we’re paying attention to something.

The researchers used a technique in which pin-like sensors are used to stimulate the brain and record activity in a particular column of neurons. The activity recorded by the pins revealed that groups of neurons constantly cycled in unison between on and offline states.

“During an ‘on’ state the neurons all start firing rapidly,” Kwabena Boahen, a bioengineer at the university and senior author of the study, said in a statement. “Then all of a sudden they just switch to a low firing rate. This on and off switching is happening all the time, as if the neurons are flipping a coin to decide if they are going to be on or off.”

Scientists already knew that individual neurons tend to shift between more and less active states, but this was the first time that the effect was observed in groupings of neurons, similarly to what occurs during sleep.

These activity cycles relate to our ability to respond to the environment and therefore may play a role in selective attention. The researchers observed that when monkeys were paying attention to a visual cue, the neuronal column that was responsible for sensing that part of the environment spent more time in the active state.

“This on and off switching is happening all the time, as if the neurons are flipping a coin to decide if they are going to be on or off.” - Stanford University bioengineer Kwabena Boahen

In fact, the more that the neurons remained in the on state, the more likely the monkeys were to successfully identify a change in the environment. When the neurons were offline, they were significantly less likely to detect the change. This might be one explanation for why we sometimes miss things, even when we think we’re paying attention.

“Attention and arousal are tightly interdependent,” Dr. Tatiana Engel, a postdoctoral fellow at the university and one of the study’s authors, told The Huffington Post. “It appears as if during attention small parts of the brain become a little more aroused.”

Still, it’s not entirely clear why neurons turn off while we’re awake. These cycles are likely the brain’s way of conserving energy, and it’s also possible that low-activity states give the neurons a chance to clear out waste that’s generated as a byproduct of neural activity (an important function that the brain also performs during sleep). More research needs to be done to confirm either of these possibilities.