Can a lack of sleep drive you crazy?

Scientists in the U.S. have linked a lack of sleep to mental illness; they say brain scans can show how the brain gets tired and over-emotional when someone is deprived of sleep.

The researchers from Harvard Medical School and the University of California at Berkeley used functional magnetic resonance imaging (fMRI) to look at the brains of sleep-deprived volunteers.

The researchers found huge increases in brain activity when the sleepless participants were shown 100 different images, ranging from emotionally neutral to negative, designed to make them angry or sad.

fMRI allows scientists to look at blood flow in the brain in real-time, showing where the brain is most active.

The researchers found that the parts of the brain linked to emotional reactions, the amygdala, showed bigger reactions (over 60% more) to the images compared with a normally-rested volunteer.

Researcher Matthew Walker says the size of the increase was surprising and was as if without sleep, the brain reverts back to a more primitive pattern of activity, becoming unable to put emotional experiences into context and produce controlled, appropriate responses.

He suggests that the findings might shed light on the connection between sleep and psychiatric disorders.

Walker says there is clinical evidence that some form of sleep disruption is present in almost all psychiatric disorders and the findings might shed light on that connection.

Researchers say the results are the first to explain on a scientific level how lack of sleep may lead to emotionally irrational behavior.

But experts say psychiatric problems cannot be solely blamed on a lack of sleep.

The study does however add to a long list of the negative effects of a lack of sleep on health.

The brain needs sleep to function and Walker says sleep appears to restore our emotional brain circuits, and in doing so prepares us for the next day's challenges and social interactions.

The research is published in the journal Current Biology.