When we are awake, we typically believe that our minds are always racing with ideas. We maintain our own dynamic mental stream, which is like a river stream that never stops flowing.

A thought may lead to another, whether or not it is important to what we do, and it may ebb and flow between our inner world and the outside world.

But how does the brain manage to stay in such a thought-related condition all the time? According to a recent study that was published in the Proceedings of the National Academy of Sciences, it truly cannot be done because our brains must occasionally "go offline," which we can perceive as mental voids.

Re-analysing a previously gathered dataset, researchers from the University of Liege, EPF Lausanne & University of Geneva asked healthy subjects to describe their mental state as it was just prior to receiving an auditory probe (beep) while lying still in the MRI scanner. The options were environmental perceptions, thoughts influenced by stimuli, ideas unaffected by stimuli, and mental lapses.

Using this experience-sampling technique, good photos were gathered.

In contrast to the other states, mental blanking episodes were recorded much less frequently and recurred much less frequently over time, according to the researchers. The researchers also discovered, using machine learning, that during episodes of mind-numbing, our brains arranged so that all brain regions were in constant communication with one another.

The high amplitude of the fMRI global signal, a surrogate for low cortical arousal, further distinguished this ultra-connected brain pattern. To put it another way, when we describe mind blanking, our brains appear to be in a state that is comparable to deep sleep, except that we are awake.

"Mind blanking is a relatively new mental state within the study of spontaneous cognition. It opens exciting avenues about the underlying biological mechanisms during waking life. It might be that the boundaries of sleep and wakefulness might not be as discrete as they appear to be after all," says the principal investigator Dr Demertzi Athena, FNRS researcher at GIGA ULiege.

"The continuously and rapidly changing brain activity requires robust analysis methods to confirm the specific signature of mind blanking," continues Dr Van De Ville Dimitri.

According to the researchers, the rigid neurofunctional profile of mind blanking could explain why people are unable to report mental content because their brains are unable to distinguish signals in a way that is instructive.

This work suggests that instantaneous non-reportable mental events might occur during wakefulness, establishing mind blanks as a significant mental state during the current experience while we wait for the underlying mechanisms to be clarified.