To find out what might be happening to this CSF flow in the sleep-deprived brain, Lewis, who is also a member of MIT’s Institute for Medical Engineering and Science, and his colleagues tested 26 volunteers in the laboratory on a number of cognitive tasks after they woke up and when they were well-rested. Using both electroencephalogram and functional magnetic resonance imaging, researchers measured heart rate, breathing rate, pupil diameter, blood oxygenation in the brain, and CSF flow in and out of the brain while participants tried to press a button when they heard a beep or saw a visual change on the screen.
Not surprisingly, sleep-deprived participants performed much worse than well-rested participants. Their reaction times were slow, and in some cases the participants never noticed the stimulus.
Researchers identified several physiological changes during these lapses of attention. Most important was the flow of CSF from the brain, which returned as soon as a lapse occurred – and as soon as it ended. Researchers speculate that when the brain is sleep-deprived, it “attempts to catch up with this process by initiating waves of CSF flow,” as Lewis says, even at the expense of one’s ability to pay attention.
“One way to think about those phenomena is that your brain needs so much sleep, it does its best to enter a sleep-like state to restore some cognitive functions,” says postdoctoral associate and lead author Xinong Yang. paper At work.
The researchers also found several other physiological phenomena associated with attention lapses, including constriction of pupils as well as reductions in breathing and heart rate. They found that pupil contraction began approximately 12 seconds before CSF exited the brain, and the pupil dilated again after attention was returned.
“When your attention fails, you can feel it perceptually and psychologically, but it’s also reflective of an event that’s happening throughout the brain and body,” says Lewis.
“These results suggest to us that there is an integrated circuit that controls very high-level functions of the brain – our attention, our ability to understand and respond to the world – and then also really basic, fundamental physiological processes.”
The researchers haven’t figured out what this circuit might be, but a good candidate, they say, is the noradrenergic system, which regulates many cognitive and physiological functions through the neurotransmitter norepinephrine — and has recently been shown to oscillate during normal sleep.
