It’s a fairly obvious statement that when we don’t sleep enough, we can be irritable and oversensitive. Researchers in Israel say they now found the brain mechanism that makes that happen.
Participants in the research conducted at Tel Aviv Sourasky Medical Center and Tel Aviv University were asked to recall a series of numbers and identify patterns of rapid movement when neutral photos (such as of colleagues at work) or emotional photos (such as of a crying baby) were presented. They were asked to ignore the photos so they could carry out the assignment while constantly overcoming their emotional reactions.
The researchers focused on the activity of the amygdala, the brain’s central region for processing emotions, as well as the activity of the frontal regions responsible for regulating emotional reactions.
As expected, the reaction of the amygdala was stronger in response to emotional photographs when the participants were alert (after a night’s sleep of seven to nine hours). But after 24 hours of the sleeplessness, the researchers were surprised to discover that in addition to emotional pictures affecting the amygdala, the effect was identical also for neutral pictures, hinting at an undiagnosed emotional reaction. In addition, the activity in the frontal regions that regulate emotional activity was significantly reduced.
Examining the sleep habits of the participants showed that emotional over-activity was connected to the small amount of REM (rapid eye movement) sleep, which occurs when people dream and sleep deeply; this discovery supported the importance of this phase in sleep for emotional processing, the researchers said.
The study showed that nights without sleep cause a decline in the “emotional activation threshold” of the brain, which creates an exaggerated emotional reaction even to neutral stimulation and profound decline in cognitive control of emotion.