Why Does Your Brain Go Blank?

Sometimes your brain seems like it's not working, and that might actually be a sign that it's doing its job very well. Popular Science reports that according to a recent study published by cognitive neuroscientist Athena Demertzi, mind blanking—those strange moments when nothing's going on upstairs—might occur between 5% and 20% of the time. These are those moments when you just zone out, don't remember what you were thinking, or just stop paying attention with nothing else running through your brain. "Mind blanking is the impression of having no thoughts or not being able to report any," said Demertzi. But the science of nothing is actually pretty complicated.

That mysterious pause in thought turns out to be tightly linked to brain arousal—how stimulated or alert we are. When arousal dips too low, the brain struggles to keep up a continuous stream of thought, and mind blanking becomes more likely. But there's a catch: Too much arousal doesn't help, either. At very high levels, heightened focus tips into anxiety, producing a blur of racing thoughts that are difficult to recall—yet another kind of blank. "We know that it manifests in clinical states like ADHD," says Demertzi, noting that children with the condition, especially when unmedicated, report more frequent blank episodes.

But the bigger question Demertzi wants to answer is why mind blanking happens in the first place. One clue, she says, might lie in what our brains do during sleep: using the glymphatic system to clear out waste. "When we sleep, our neurons are getting rest by throwing away what has been accumulated throughout the day," she explains. Some researchers, including Demertzi, suspect that our brains may take micro-rests while we're still awake, and we experience those as momentary blanks. And while it may seem like a "brain fart," Demertzi said these brief mental resets might be essential for keeping cognitive performance sharp. "How can you sustain a continuous wakeful life if our brains are not helping a bit?" (More neuroscience stories.)