If only I could get some sleep (Image: Gary Houlder/Getty)
Dark puffy eyes, a feeling of deep exhaustion, and a foul mood to match 鈥� we鈥檝e all experienced the side effects of a lack of sleep. It鈥檚 no wonder that sleep-deprivation has been used as a method of torture.
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Our brains seem to lose the ability to distinguish between the innocuous and emotional in such circumstances, turning us into overreacting, exhausted wrecks.
We all know that a good night鈥檚 sleep is vital for a day of clear thinking, but exactly why sleep is so important remains a mystery. of Tel Aviv University in Israel is particularly interested in how lack of sleep leaves us with a short emotional fuse. 鈥淲e know that sleep affects our emotional behaviour, but we don鈥檛 know how,鈥� she says.
To investigate further, Hendler and her colleagues kept 18 adults awake all night. 鈥淚t took a great effort,鈥� she says. 鈥淒uring the night, we repeatedly measured their sleepiness, and unsurprisingly they got more and more tired.鈥�
The volunteers were put through two rounds of tests while their brains were scanned, both the day after a good night鈥檚 sleep and after being awake for 24 hours. In one test, volunteers were asked to give the direction in which yellow dots moved on a screen. In each case, the dots were laid over a potentially distracting picture that was either positively emotional (of a kitten or a couple in love, for example), negatively emotional (such as a mutilated body or a snake) or neutral (such as a cow or spoon).
When the volunteers were well-rested, they were quickest and best at telling the direction of movement when the background image was neutral. But after a night without sleep, their performance was equally bad whether neutral or emotional images were used.
That might simply be because a sleepless night universally impairs judgement, but it鈥檚 also possible that the result hints at something more subtle 鈥� that lack of sleep makes neutral images suddenly provoke an emotional response, says Hendler.
Scanning the detail
To probe the link in more detail, her team conducted a similar experiment in an fMRI scanner, which is used to measure activity in different areas of the brain.
Inside the scanner, volunteers were again shown potentially distracting neutral and emotional images while they tried to complete a task 鈥� and again, sleep-deprived people found all images distracting, whereas the non-sleep-deprived were only distracted by emotional images.
Moreover, a region of the brain called the amygdala, which is known to play a part in emotion, fired up in response only to emotional images when the volunteers had had a good night鈥檚 sleep. But when they were sleep-deprived, it reacted to neutral images in the same way as emotional ones.
The team also found unusual activity in a frontal part of the brain called the anterior cingulate cortex (ACC), which is thought to regulate the amygdala and our emotions. In well-rested people, the two brain regions fired together. But they seemed out of sync when the volunteers were sleep-deprived, with the ACC tending not to fire when the amygdala did. As a result, this part of the brain doesn鈥檛 seem as able to control our emotional responses when we don鈥檛 get enough sleep, says Hendler.
Together, the experiments suggest that when we鈥檙e sleep-deprived we tend to see normal, everyday situations as particularly worthy of our attention, says Hendler. 鈥淵ou lose neutrality,鈥� she says. 鈥淭he ability of the brain to tell what鈥檚 important is compromised 鈥� it鈥檚 as if everything is important.鈥�
There is one obvious way to protect yourself from the effects of sleep loss: try to get enough shut-eye. Hendler thinks people might also be able to strengthen the connection between the ACC and amygdala using neurofeedback 鈥� a technique that uses brain-monitoring technology to allow people to record and watch their own brain activity and attempt to control it.
But at Brown University in Providence, Rhode Island, isn鈥檛 sold on the idea. 鈥淒espite wishes some have to the contrary, we all need sleep,鈥� she says. 鈥淚 don鈥檛 want to stimulate the activity between my amygdala and frontal cortex 鈥� I want to get plenty of sleep.鈥�
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