Teenagers’ brains don’t respond well to reward if they have "social jet lag"

Remember when you were a teenager and the weekends were your chance to catch up on all that sleep you missed during the week? If you were a normal teenager at a normal school, you probably missed sleep during the week because of all the fun social activities you had and the fact that school started too early in the morning. If you were a nerd like me, at a nerd school, it was because you had about 5 hours of homework a night and a calculus teacher that insisted your calculus homework should only take half an hour because that’s how long it took her to do it. I digress.
It turns out that a major imbalance in sleep between weekdays and weekends for adolescents is not a good thing at all. This shift in sleep is something researchers call “social jet lag”. A paper from the labs of Ron Dahl and Erika Forbes was just released in Biological Psychology with results from a study showing that brain structures of adolescents with this kind of sleep imbalance just don’t respond as much to monetary rewards as adolescents with a more consistent sleep pattern across the week. They found that this lack of response had more to do with the shift in sleeping time rather than the total number of hours slept – in other words, it wasn’t just sleep deprivation that was associated with the change in brain function.
Why do we care if teenagers’ brains don’t respond to reward? It’s associated with a lot of bad outcomes, including increased risk-taking behaviours, substance abuse, and even mood disorders like depression. Previous studies have shown that social jet lag in adolescents has been linked to these sorts of behaviours, but this study is the first to show a neural basis for the association.
However, this study only looked at the kids at one point in time, so the authors do point out that we can’t be sure if the sleep problems were causing the lack of brain response, or if the lack of response to reward meant that adolescents were looking for bigger “thrills” by staying up late on the weekends. We need more longitudinal research to answer these kinds of questions, i.e., studies that follow up kids over a number of years.
These guys consistently put out top-quality research informing our knowledge of adolescent development so it’s great to see some work by them supporting the importance of sleep hygiene (i.e., good sleeping habits) in this age (although I should disclose a conflict of interest in that my lab is currently collaborating on a sleep intervention trial with Ron Dahl).
You can read the abstract for this study here.

3 thoughts on “Teenagers’ brains don’t respond well to reward if they have "social jet lag"

  1. I wonder if a similar effect can be found in adults. A study in adults found that exposure to light during the evenings could lead to depression: http://healthland.time.com/2012/07/24/unplug-too-much-light-at-night-may-lead-to-depression/I wonder if there's a similar thing at work here. Social jet lag requires them to be awake more often, and presumably that's because they're up on computers, watching tv or out with friends. In any event, it seems clear that messing with our natural sleep patterns has some pretty serious consequences.

  2. @James Hill: Social jet lag certainly exists in adults as well, and the link between poor sleep habits and depression has been a topic of investigation for awhile, as has the link between light and depression. In adults it's been found that the less illuminance, the higher the depression scores: http://tinyurl.com/c7vbdncand that light therapy appears to improve not just Seasonal Affective Disorder (http://tinyurl.com/cykqxf3),but other types of depression that aren't season-dependent, too (http://tinyurl.com/cajwn58).On the other hand, too much blue light right before bed (in things like computers, TVs, phone screens) can be bad for sleep because it inhibits melatonin: http://www.ncbi.nlm.nih.gov/pubmed/21552190(in fact one company has created blue light blocking glasses to deal with this issue: http://www.mcsaustralia.com.au/light-therapy/low-blue-light-glasses.html)So although light is a good thing, what's important is when you're exposed to it. One good tip is to leave your blinds open at night so when the sun rises in the morning, you get a good dose of natural sunlight to help you wake up. But if you live in the city with lots of unnatural light blaring through your window at night, this can work against you.

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