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If you thought poor sleep habits only affected teenagers’ mental well being, academic performance, memory retention, hormone levels and cardiovascular health, don’t worry — the ill effects of shoddy adolescent shut-eye don’t stop there.

A new study, published in Developmental Cognitive Neuroscience, offers evidence that poor sleeping habits have long-term effects on teen brain development.

During adolescence, the brain experiences a vital growth sprint, including a process called “neural pruning.” During this stage, the brain sheds unnecessary neurons (the building blocks of gray matter) to make room for additional white matter fibers, which connect neurons and insulate brain structures. This is called myelination.

The additional white matter improves processing speed and connectivity of the pre-frontal cortex. This is the area of the brain that’s central to mental processes, such as impulse control and decision-making, which are famously weak in teens. Additionally, the teen brain is highly “plastic” during periods of development, meaning it’s unusually susceptible to environmental influence.

Cognitively speaking, becoming an adult hinges on the white-matter uptick that caps off teenagehood. But sleeping issues common among the youths may interfere with the growth of white matter.

The Study:

Forty-eight high school-aged teenagers kept daily sleep diaries for two 14-day periods during fall semester, a year apart. They wrote down when they went to sleep and woke up, as well as how many hours they slept.

Within a few months of the second diary period, the teenagers underwent brain scans. Researchers used a specialized type of Magnetic Resonance Imaging (MRI), called DTI, which captures white matter in detail. They performed the brain scans six months and (roughly) a year-and-a-half after the respective diary periods. Researchers were looking for a connection between erratic sleep and white matter growth.

Indeed, they saw a link between lower levels of white matter and varied sleep patterns. But only in comparison to the first diary period, not the second. This suggests that poor sleep took more than one year to affect brain development. Furthermore, participants who reported inconsistent sleep duration during the week demonstrated lower white matter. Researchers didn’t find the same link between white matter levels and bedtimes, waking times, or even duration differences in weekend vs. weekday sleep.

It appears that, for the sake of long-term brain development, the most important behavioral factor is a consistent amount of sleep on a day-to-day basis.

The study is among the first to measure the impact of sleep schedules on adolescent white matter levels. It suggests that teenagers should prioritize getting the same amount of sleep in between filling out college apps and sexting strangers. Erratic sleep duration seems to play a role in white matter growth, a crucial part of the cognitive coming-of-age process.

But that’s about all we know. It may be the case, the study says, that we’ve flipped the causal relationship — paltry white matter could lead to wonky sleeping patterns, rather than the other way around. Additionally, observing structural brain differences is only half of the equation. Future research needs to establish a connection between white matter levels and the suspected cognitive and behavioral consequences.

Different doesn’t always mean deficient. But, if rebelling against sleep recommendations means graduating high school with an under-myelinated brain, then, in this case, conformists probably have the edge.

Stay tuned to Van Winkle’s for more research on sleep and cognition.