Study Links Teen Sleep Patterns to Brainpower — But Not Grades

Credit: Adobe Stock/ Pixel-Shot

A recent study found adolescents with a lower heart rate who sleep earlier and longer perform better than peers with a different sleep biotype in tasks related to crystallized intelligence, picture vocabulary and oral reading recognition — but not academic achievement.

Countless studies demonstrate that grogginess from too little sleep can cloud judgment. Most people know the feeling of dragging yourself to work or school with their brain still foggy from exhaustion.

But this study, led by Qing Ma, from the school of psychology and cognitive science at East China Normal University in Shanghai, dug deeper into the link between impaired sleep and cognition in adolescents, identifying two key sleep-brain dimensions and three sleep biotypes among adolescents.

“Regularly getting a good night’s sleep is important in helping us function properly, but while we know a lot about sleep in adulthood and later life, we know surprisingly little about sleep in adolescence, even though this is a crucial time in our development,” said Barbara Sahakian, from the Department of Psychiatry at the University of Cambridge, in a statement. “How long do young people sleep for, for example, and what impact does this have on their brain function and cognitive performance?”

Researchers analyzed data from 3,222 adolescents in the Adolescent Brain Cognitive Development (ABCD) study, integrating sleep characteristics with multimodal imaging. The team examined 85 indices of brain volume, 282 indices of functional connectivity and 18 digital measurements for sleep, including how long it takes adolescents to begin sleep and have deep sleep and how many hours of sleep they receive, along with other parameters.

This analysis revealed two key sleep-brain dimensions: linking later sleep onset and shorter duration to decreased subcortical-cortical connectivity and associating a higher heart rate and shorter light sleep with lower brain volumes and connectivity. The team identified three sleep biotypes among adolescents: delayed, shorter sleep with a higher heart rate (biotype 1); earlier, longer sleep with a lower heart rate (biotype 3); and somewhere in the middle (biotype 2). Biotypes 1, 2 and 3 encompassed 1,252 individuals, 784 individuals and 1,186 individuals, respectively.

These biotypes had variations in brain structure and function, ultimately affecting cognitive performance, and a longitudinal analysis confirmed these differences from ages 9 to 14 years old. Adolescents with biotype 3 — earlier, longer sleep and a lower heart rate — had the most cognitive benefits.

“Although our study can’t answer conclusively whether young people have better brain function and perform better at tests because they sleep better, there are a number of studies that would support this idea,” Ma said in a news release. “For example, research has shown the benefits of sleep on memory, especially on memory consolidation, which is important for learning.”

Adolescents with biotype 3 had larger brain volumes than biotypes 2 and 1. Biotype 2 also had a larger brain volume than biotype 1.

The study also examined cognitive and brain profile changes over 4 years from 9 to 10 years old to 13 to 14 years old. All biotypes showed improvement in cognitive abilities over the 4 years in crystallized intelligence, picture vocabulary, oral reading recognition and performance on the flanker test.

Biotype differences observed at ages 11 to 12 remained consistent at ages 9 to 10 years and 13 to 14 years. Over time, the three biotypes showed no difference in academic achievement.

“Given the importance of sleep, we now need to look at why some children go to bed later and sleep less than others,” senior author Wei Cheng, from Fudan University, said in the news release. “Is it because of playing video games or smartphones, for example, or is just that their body clocks do not tell them it’s time to sleep until later?”