And why it's a problem even coffee can't solve. 

By Grace Elkus
Updated December 08, 2015
Cranky Woman in Bed
Credit: Images

Cranky and on-edge after a poor night’s sleep? A small new study suggests it might not be your fault.

According to researchers from Tel Aviv University, exhaustion affects your brain’s ability to control emotion—making you react irrationally to every little thing. The results are published in the Journal of Neuroscience.

Eighteen adults participated in the study, in which they were kept awake all night to take two rounds of tests. The participants took the first test following a good night’s sleep, and the second following a poor night's sleep. Brain mapping technology was used to measure their responses.

In the first experiment, they were asked to describe the direction of small yellow dots moving over distracting images of a cat (positively emotional), a mutilated body (negatively emotional), or a spoon (neutral).

After a good night’s sleep, participants identified the direction of the dots over the neutral images more quickly and accurately. After a poor night’s sleep, participants' performance suffered in response to both the neutral and emotional images, prompting researchers to believe fatigue causes neutral images to rouse emotional responses.

In the second experiment, which tested concentration levels, the participants were shown both neutral and emotional images while performing a task that demanded their attention. After a night of poor sleep, the participants were distracted by every single image, and well-rested participants were only distracted by emotional images.

“It turns out we lose our neutrality,” Prof. Talma Hendler, lead researcher of the study, said in a statement. “The ability of the brain to tell what's important is compromised. It's as if suddenly everything is important.”

In need of advice for how to catch more Zzz's? Here are Real Simple readers' secrets to longer, deeper sleep.