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Saturday, April 13, 2024

UC Davis Sleep Lab looks into the correlation between sleep need and age

Study finds shorter sleep durations lead to a decrease in EEG waves

In a recent study restricting sleep durations in adolescents, the UC Davis Sleep Lab found that shorter sleep durations led to a significant decrease in waking EEG power. This is just one part of the laboratory’s long history of looking at sleep in adolescents.

According to Ian Campbell, the associate project scientist in the department of psychiatry and behavioral sciences, the Sleep Lab started its adolescent studies in 2002 when they initially began looking into how sleep and EEG brain waves change across childhood and adolescence.

“What was special about that study, what made it different from all previous studies, is that it was longitudinal,” Campbell said. “So we followed the same people over time. Previous studies had been cross-sectional, so they compared the brain waves of like a nine year old to a 15 year old and would look at how they were different. By following the same kids over time, we are able to very precisely determine how sleep and the EEG brain waves change across adolescence.”

The study found that total sleep time between the ages of nine and 18 decreased by approximately 10 minutes per year, which was correlated with a decline in the time they spent in bed. The decline in total time in bed was not caused by earlier waking times, but rather by going to sleep later. Hans P. A. Van Dongen, the director of Sleep and Performance Research Center and professor of Elson S. Floyd College of Medicine at Washington State University, has also studied studied the effects of sleep and sleep deprivation on performance and came to similar conclusions.

“Sleep need is not the only aspect of sleep that changes with age – so is the optimal timing of sleep,” Van Dongen said. “This applies to adolescents who have trouble getting out of bed in the morning – they are not “lazy” as is often assumed, just aren’t ready to wake up yet in the early morning hours. And it also applies to older adults, who may gradually wake up earlier and earlier in the morning and think they cannot get enough sleep anymore – but may actually get more sleep if they would also go to bed earlier in the evening than they may have been used to.”

Campbell also said that the research found that this decrease in sleep duration was entirely in non-rapid eye movement sleep, with an increase in REM sleep. In addition, although Campbell and his team had prior knowledge that children have more slow wave activity than adults, they were unsure whether this was a gradual or abrupt change.

“We were particularly interested in these big slow waves because these big slow waves are an indicator of a type of recuperation that happens during sleep,” Campbell said. “If somebody has been awake longer, they will have more of this slow wave activity. If somebody takes a nap in the afternoon, then they will have accomplished some of the night time recuperation during that nap and they’ll have less of that slow wave activity at night.”

The longitudinal study showed that slow wave activity was fairly constant between the ages of six and 12, but their delta power plummeted from there until age 16. Campbell stated that he thinks that during this period, the adolescent brain changes in a way that there is a decreased need for recuperation throughout sleep, which may be driven by synaptic pruning. By comparing females and males, the team found that this change occurred earlier in females, a finding they attributed to puberty, though they are unsure whether puberty causes the EEG change or if a mechanism upstream triggers both occurrences.

“We did not think it was going to be related to puberty,” Campbell said. “We thought these were two totally independent things, that sexual maturation was one thing and the synaptic pruning that’s causing the EEG changes was something different. There’s was no reason for them to be linked in time and [we were] surprised that they were.”

With this portion of their study ending in 2012, Campbell and his team are currently running a dose-response study determining whether sleep need decreases, increases or remains unchanged throughout adolescence and into early adulthood.

There have been various previously conducted studies that looked into sleep need in adolescents. Mary A. Carskadon, professor of psychiatry and human behavior at Alpert Medical School of Brown University and director of chronobiology and sleep research at EP Bradley Hospital, published an article June of 2011 titled “Sleep in Adolescents: The Perfect Storm” about how adolescents’ loss of sleep is not driven by a lower need for sleep, but rather a combination of biological, psychological and socio-cultural influences. She believes that many people have misconceptions about adolescents being able to obtain an adequate amount of sleep by going to sleep earlier.

“For many teens this is just not feasible, given the biological process that are also reinforced by modern ‘conveniences’ that provide reasons to stay awake late,” Carskadon said. “That said, if we lived by the rule of daylight and darkness, which of course we do not, the issues would not manifest as they now do. On the other hand, I suspect that adolescents would still carve out a temporal niche that is later than that inhabited by grown ups.”

In Campbell’s current study, participants are assigned to spend either seven, eight and a half or 10 hours in bed and then come into the laboratory for performance testing, which is then compared with their prior sleep duration. The researchers will follow these participants over time to discover whether this relationship changes with age. In their most recently published paper, “shorter sleep durations in adolescents reduce power density in a wide range of waking electroencephalogram frequencies.” They found that from 10 hours in bed to seven hours in bed, waking EEG power declined significantly. As they have already conducted studies on individuals from ages 10 to 14, Campbell hopes that by studying people of ages 15 to 20 they will be able to attain a more firm answer on how daytime performance is related to age and how this changes with age.

“This idea that sleep is not important, that I can stay up all night and study and still perform well the next day is not a good approach to life,” Campbell said.  

Written by: Michelle Wong — science@theaggie.org


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