Irritable? You may only just lack sleep.

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You might have guessed it, but now researchers have real proof: Sleep deprivation causes our emotions to go haywire.

That's according to the first neurological probe into the emotional brain without sleep. It was carried out by researchers at the University of California-Berkeley and Harvard Medical School.

"Most people think that when you're sleep-deprived, what happens to the brain is that it becomes sleepy and less active," says Matthew Walker, assistant professor of psychology at Berkeley and a former Harvard sleep researcher. But Walker says the imaging study published in today's issue of Current Biology found that the brain's emotional centers become "60% more reactive."

The study also suggests that lack of sleep elevates activity in the emotional centers of the brain most closely associated with psychiatric disorders such as depression.

I find this amusing because I really do get irritable if I lack sleep. I guess now I can justify scientifically my occasional irritability!