Sleep deprivation hits some brain areas hard

Pulling consecutive all-nighters makes some brain areas groggier than others. Regions involved with problem solving and concentration become especially sluggish when sleep-deprived, a new study using brain scans reveals. Other areas keep ticking along, appearing to be less affected by a mounting sleep debt.

The results might lead to a better understanding of the rhythmic nature of symptoms in certain psychiatric or neurodegenerative disorders, says study coauthor Derk-Jan Dijk. People with dementia, for instance, can be afflicted with “sundowning,” which worsens their symptoms at the end of the day. More broadly, the findings, published August 12 in Science, document the brain’s response to too little shut-eye.
“We’ve shown what shift workers already know,” says Dijk, of the University of Surrey in England. “Being awake at 6 a.m. after a night of no sleep, it isn’t easy. But what wasn’t known was the remarkably different response of these brain areas.”

The research reveals the differing effects of the two major factors that influence when you conk out: the body’s roughly 24-hour circadian clock, which helps keep you awake in the daytime and put you to sleep when it’s dark, and the body’s drive to sleep, which steadily increases the longer you’re awake.

Dijk and collaborators at the University of Liege in Belgium assessed the cognitive function of 33 young adults who went without sleep for 42 hours. Over the course of this sleepless period, the participants performed some simple tasks testing reaction time and memory. The sleepy subjects also underwent 12 brain scans during their ordeal and another scan after 12 hours of recovery sleep. Throughout the study, the researchers also measured participants’ levels of the sleep hormone melatonin, which served as a way to track the hands on their master circadian clocks.

Activity in some brain areas, such as the thalamus, a central hub that connects many other structures, waxed and waned in sync with the circadian clock. But in other areas, especially those in the brain’s outer layer, the effects of this master clock were overridden by the body’s drive to sleep. Brain activity diminished in these regions as sleep debt mounted, the scans showed.

Sleep deprivation also meddled with the participants’ performance on simple tasks, effects influenced both by the mounting sleep debt and the cycles of the master clock. Performance suffered in the night, but improved somewhat during the second day, even after no sleep.
While the brain’s circadian clock signal is known to originate in a cluster of nerve cells known as the suprachiasmatic nucleus, it isn’t clear where the drive to sleep comes from, says Charles Czeisler, a sleep expert at Harvard Medical School. The need to sleep might grow as toxic metabolites build up after a day’s worth of brain activity, or be triggered when certain regions run out of fuel.

Sleep drive’s origin is just one of many questions raised by the research, says Czeisler, who says the study “opens up a new era in our understanding of sleep-wake neurobiology.” The approach of tracking activity with brain scans and melatonin measurements might reveal, for example, how a lack of sleep during the teenage years influences brain development.

Such an approach also might lead to the development of a test that reflects the strength of the body’s sleep drive, Czeisler says. That measurement might help clinicians spot chronic sleep deprivation, a health threat that can masquerade as attention-deficit/hyperactivity disorder in children.