KEY POINTS:
It's long been known that a lack of sleep can make us grumpy and irrational, but now scientists believe they have pinpointed why.
In the first neural investigation into what happens to the emotional brain when we sleep, researchers from the University of California, Berkeley, and Harvard Medical School found that sleep deprivation causes the part of the brain which controls depression, anxiety and other psychiatric disorders to become more active.
"It's almost as though, without sleep, the brain had reverted back to more primitive patterns of activity, in that it was unable to put emotional experiences into context and produce controlled, appropriate responses," said Matthew Walker, director of UC Berkeley's Sleep and Neuroimaging Laboratory and senior author of the study, which is to be published in the journal Current Biology.
"Emotionally, you're not on a level playing field," Walker told the Science Daily website.
The researchers found that the amygdala, the region of the brain that alerts the body to protect itself in times of danger, goes into overdrive when a person is deprived of sleep.
As a flow-on effect, the prefrontal cortex, which commands logical reasoning, shuts down and prevents the release of chemicals which would usually calm down the fight-or-flight reflex.
In a normally functioning brain, the relationship between the amygdala and the prefrontal cortex is what allows us to distinguish between what is make-believe and what is real.
When we watch a violent movie, for example, even if the amygdala reacts strongly to it, the prefrontal cortex registers that the scene is not real and controls our reaction to it.
But instead of connecting to the prefrontal cortex, the researchers found that sleep-deprived brains connected to the locus coeruleus - the oldest part of the brain - which releases noradrenalin to ward off imminent threats to survival, posing a volatile mix.
The scientists studied 26 healthy participants aged 18 to 30, breaking them into two groups of equal numbers of males and females.
The sleep-deprived group stayed awake for 35 hours straight, while the control group stayed awake during the day but were allowed to sleep normally during the night.
Functioning Magnetic Resonance Imaging (fMRI) was performed at the end of day two of the test, with each person was shown 100 images that ranged from neutral (an empty wicker basket on a table) to very negative (pictures of mutilated bodies).
Using this emotional gradient, the researchers were able to compare the increase in brain response to the increasingly negative pictures.
Those participants who got a full night's sleep in their own beds showed normal activity in the amygdala.
However those who had been deprived of sleep registered extreme emotional reactions to the images.
The researchers' findings have laid the groundwork for further investigation into the relationship between sleep and psychiatric illnesses.
Clinical evidence has shown that some form of sleep disruption is present in almost all psychiatric disorders.
"This is the first set of experiments that demonstrate that even healthy people's brains mimic certain pathological psychiatric patterns when deprived of sleep," Walker told Science Daily.
"Before, it was difficult to separate out the effect of sleep versus the disease itself. Now we're closer to being able to look into whether the person has a psychiatric disease or a sleep disorder."
- NZ HERALD STAFF
