A new study reveals that lack of sleep causes the brain to perform its cleaning process while awake, leading to momentary lapses in attention. Researchers found that cerebrospinal fluid flushes occur just before focus is lost. This explains the difficulty in concentrating after a bad night's sleep.
We all know sleep deprivation impairs concentration, but a study published in Nature Neuroscience explains why. During normal sleep, the brain flushes cerebrospinal fluid (CSF) through its tissues to clear metabolic waste and prevent damage to brain cells. When sleep is insufficient, this rinsing process shifts to wakefulness, causing brief attention lapses.
Laura Lewis at the Massachusetts Institute of Technology and her colleagues tested this with 26 participants aged 19 to 40. First, the group got a good night's sleep, feeling well-rested. Two weeks later, they were kept awake all night in a lab. The next morning in both scenarios, MRI scans recorded brain activity as participants completed tasks: pressing a button upon hearing a specific tone or seeing a cross on a screen turn into a square, repeated dozens of times over 12 minutes.
As expected, sleep-deprived participants failed to respond substantially more often, indicating poorer focus. Analysis showed lapses occurred about 2 seconds before CSF flushed from the brain's base, with fluid returning about 1 second after attention recovered.
"If you think about the brain-cleaning process like a washing machine, you kind of need to put the water in and then slosh it around and then drain it out, and so we’re talking about the sloshing part occurring during these lapses of attention," says Lewis.
The findings suggest the brain compensates for missed nighttime cleaning by sneaking in waves during the day, at the cost of concentration. "If you don’t have these waves [of fluid flowing] at night because you’re kept awake all night, then your brain starts to kind of sneak them in during the daytime, but they come with this cost of attention," Lewis adds. Why this impairs attention is unclear, but identifying involved brain circuits could help mitigate sleep deprivation's cognitive effects.