How are sleep and emotional state related? Apparently, after a sleepless night, the brain ceases to clearly distinguish between what requires an emotional reaction and what does not. This is why we often overreact to everything that happens around us, which exhausts us even more.
Everyone knows that for clear thinking we need to get enough sleep, but the mechanisms of this connection to science are still not completely clear. Talma Hendler from Tel Aviv University (Israel) tried to understand why lack of sleep leads to overly emotional reactions.
18 volunteers took part in her experiment. They spent a sleepless night, during which the researchers repeatedly tested how sleepy the participants were: it’s no surprise that over time they wanted to sleep more and more.
The subjects underwent brain scans — once after a full night’s sleep, and the second after 24 hours of wakefulness.
During the scan, the volunteers performed tasks, such as determining which direction the yellow dots on the screen were moving. At the same time, the dots moved against the background of various images, some of which could be classified as pleasant (kittens, couples in love), some as unpleasant (mutilated bodies, snakes), and the rest as neutral (a cow or a spoon).
When the subjects completed the task after a night of sleep, they quickly determined the direction of movement of the dots against the background of emotionally neutral images. But after a sleepless night, their results were equally bad, regardless of whether the background image was neutral or emotionally charged.
Perhaps the fact is that lack of sleep negatively affects all aspects of the brain, but there is another version. It is possible that a sleep-deprived brain begins to react emotionally to neutral stimuli as well.
To get a more detailed picture, a group of researchers led by Talma Hendler conducted another experiment. This time they used functional magnetic resonance imaging, which can be used to evaluate the activity of different areas of the brain. Subjects were shown similar images during brain scans, and the result was the same.
The sleepy were distracted by all the images, rested — only those that carried an «emotional charge»
They found that the amygdala (a region of the brain associated with emotions) in well-rested volunteers only activated when they saw emotionally charged images. For those who were deprived of sleep, it also reacted to neutral pictures.
The researchers also found unusual activity in a region of the subjects’ brains called the anterior cingulate cortex, which is thought to regulate amygdala activity and emotions. In the sleepy volunteers, both areas of the brain were activated at the same time.
However, in sleep-deprived people, they seemed to be out of sync — the anterior cingulate cortex often did not activate during the activation of the amygdala. Apparently, this area of the brain is not able to control our emotional reactions if we do not get enough sleep.
According to Talma Hendler, these experiments show that as a result of lack of sleep, we begin to overreact emotionally to the most ordinary everyday situations. “The brain loses the ability to distinguish the important from the unimportant, as if everything around it becomes important,” she says.
E. Simon et al. «Losing neutrality: The neural basis of impaired emotional control without sleep», The Journal of Neuroscience, September 2015.