The scientific evidence doesn't look great for regular night owls: experts say we need at least 7 hours a night to stay healthy, and interruptions to sleep can be as harmful as an overall lack of it. Now a new study says our brain's ability to regulate emotions can be compromised if we don't get enough shut-eye.

If you feel grumpy in the morning after getting to bed late, it looks like there's some scientific proof for what's going on. Researchers from Tel Aviv University in Israel were able to identify the neurological mechanism responsible for disturbing emotion regulation, and found problems started happening after just one night of sleeplessness.

Eighteen volunteers were kept up all night and subjected to fMRI (functional Magnetic Resonance Imaging) and EEG (electroencephalogram) scans to monitor the activity in their brains.

After one good night's sleep and one bad night's sleep, these participants were asked to take the same test, identifying the movement of dots over a picture. These pictures were staged to be emotionally positive (a cat), emotionally negative (a mutilated body), and emotionally neutral (a spoon). By measuring how quickly and accurately the individuals identified the movement of the dots, and combining this information with the brain scan results, the research team was able to build up a picture of cognitive processing.

Crucially, a lack of sleep pointed to decreased regulatory processing, with the EEG scans reporting very little difference in brain activity between the positive and negative images after a night of sleeplessness. A second test showed the volunteers were easily distracted by any kind of image when sleep-deprived. In contrast, after they'd had enough time in bed, only the most 'emotional' images caused spikes in brain activity.

"It turns out we lose our neutrality," said one of the researchers, Talma Hendler. "The ability of the brain to tell what's important is compromised. It's as if suddenly everything is important."

Hendler adds that before their study, scientists weren't sure what mechanism was responsible for the emotional impairments triggered by sleep loss. We've all experienced it - you had a crappy sleep the night before and everything seems to go wrong for you the next day. You snap at your partner or your dog over the tiniest annoyance.

"We assumed that sleep loss would intensify the processing of emotional images and thus impede brain capacity for executive functions," says Hendler. "We were actually surprised to find that it significantly impacts the processing of both neutral and emotionally-charged images."

What that means is that even the smallest of early morning events could cause us to fly off the handle or break down in tears after a night without sleep because our cognitive processing has been compromised. Hendler and her colleagues are now studying how various sleep intervention methods could reduce the emotional dysfunction seen in anxiety, depression, and traumatic stress disorders.

The team's work was published in The Journal of Neuroscience.