Scans shed light on changes in brain when we zone out while tired | Neuroscience

It’s never a great look. The morning meeting is in full swing, but thanks to a night out, your brain shuts down at the precise moment a question presents itself.

Such momentary lapses in attention are a common problem among sleep-deprived people, but what happens in the brain during these periods of mental shutdown proves difficult to pin down.

Now, scientists have shed light on the process and discovered that there’s more to zoning than you might think. The brief loss of concentration coincides with a wave of fluid draining from the brain, which returns once attention is restored.

“The moment someone’s attention span wanes is the moment this wave of fluid starts to pulse,” said Dr. Laura Lewis, lead author of the study at MIT in Boston. “It’s not just that your neurons aren’t paying attention to the world, there’s a big change in the brain fluid at the same time.”

Lewis and his colleague, Dr. Zinong Yang, studied the sleep-deprived brain to understand the types of attention deficits that lead drowsy drivers to crash and tired animals to become a predator’s lunch.

In the study, 26 volunteers took turns wearing an EEG cap while lying in an fMRI scanner. This allowed scientists to monitor the brain’s electrical activity and physiological changes during tests in which people were asked to react as quickly as possible when they heard a tone or saw a crosshair on a screen turn into a square.

Each volunteer was scanned after a restful night’s sleep at home and after a night of total sleep deprivation supervised by laboratory scientists. Not surprisingly, the results were much worse when sleep deprived, responding more slowly, if at all.

Losses of attention were accompanied by striking changes. The scans revealed that a wave of cerebrospinal fluid was expelled from the brain moments after the attention lapse and returned about a second after the interval ended. Such waves are normally observed during deep sleep and are thought to help the brain eliminate metabolic waste that accumulates during the day.

Further measurements showed that the pupils of the eyes contracted about 12 seconds before the fluid left the brain and returned to normal after this gap. Respiration and heart rate also decreased, the researchers report in Nature Neuroscience.

Although other questions remain, the failures appear to occur as the brain attempts to juggle normal cognitive functioning with essential maintenance normally carried out during sleep. “It’s your brain trying to take a break,” Yang said.

Professor Bill Wisden, director of the UK Institute for Dementia Research at Imperial College London, said the work highlighted the profound changes sleep deprivation could have on the brain. “It’s not clear whether these changes in brain fluid flow related to lack of sleep are good and protective in some way or bad and pathological,” he said.

Dr Ria Kodosaki, a neuroscientist at UCL, said the changes appeared to be “structured biological events that are very similar to the onset of sleep, and the lapses in attention are not passive but organized to essentially give the brain a little rest”.

She said: “As paradoxical as it may seem, these dangerous errors may be the brain’s way of protecting itself. Think of them as forced shutdowns: the brain temporarily abandons its external focus to do essential housekeeping.”