Not sleeping can cause emotional dysfunction.
The Centers for Disease Control and Prevention (CDC) call insufficient sleep a "public health problem" and estimate that 30% of Americans get less than 6 hours of sleep a night.
Lack of sleep is linked to motor vehicle crashes, industrial disasters, and medical and other occupational errors. Diseases linked to sleep insufficiency include hypertension, diabetes, depression, obesity and cancer.
Until now, it has not been clear what causes the emotional impairments triggered by sleep loss.
Neurological mechanism revealed
The new research, led by Prof. Talma Hendler of Tel Aviv University (TAU) in Israel, identifies the neurological mechanism responsible for disturbed emotion regulation and increased anxiety due to lack of sleep.
It also shows how sleep deprivation can affect our ability to regulate emotions and allocate brain resources for cognitive processing.
Researchers kept 18 adults awake all night and had them take two rounds of tests while undergoing brain mapping using functional magnetic resonance imaging (fMRI) and/or an electroencephalogram (EEG).
The first test was taken after a good night's sleep and the second after spending a night awake in the lab.
In the first test, participants had to describe the direction in which small yellow dots moved over distracting images. These images were "positively emotional" (a cat), "negatively emotional" (a mutilated body) or "neutral" (a spoon).
Sleepless night changes emotional perception
After a good night's rest, participants identified the direction of the dots hovering over the neutral images faster and more accurately, and their EEG pointed to differing neurological responses to neutral and emotional distractors.
After a wakeful night, however, they performed badly in both the neutral and the emotional image tests, and their electrical brain responses did not reflect a highly different response to the emotional images, indicating a lower degree of regulatory processing.
Fast facts about sleep
- 43% of Americans aged 13-64 years say they do not get enough sleep
- 60% have problems sleeping most nights
- Most Americans feel that 7.5 hours is an appropriate length of time to sleep.
TAU graduate student Eti Ben-Simon, who conducted the experiment, believes that sleep deprivation may universally impair judgment, but it is more likely that a lack of sleep causes neutral images to provoke an emotional response.
The second test examined concentration levels.
Participants inside an fMRI scanner had to complete a task that demanded their attention to press a key or button, while ignoring distracting background pictures with emotional or neutral content.
This time, researchers measured activity levels in different parts of the brain as participants completed the cognitive task.
After only one night without sleep, participants were distracted by every single image (neutral and emotional), while well-rested participants only found the emotional images distracting.
The effect was indicated by activity change, or what Prof. Hendler calls "a change in the emotional specificity" of the amygdala.
The amygdala is a major limbic node responsible for emotional processing in the brain. It is associated with detection and valuation of salient cues in the environment during cognitive tasks.
Prof. Hendler says:
"These results reveal that, without sleep, the mere recognition of what is an emotional and what is a neutral event is disrupted. We may experience similar emotional provocations from all incoming events, even neutral ones, and lose our ability to sort out more or less important information. This can lead to biased cognitive processing and poor judgment as well as anxiety."
The team had only expected that sleep loss would intensify the processing of emotional images and thus impede brain capacity for carrying out tasks, but they were surprised to observe a significant impact on the processing of both neutral and emotionally charged images.
A lack of sleep appears to compromise the brain's ability to decide what is important. Suddenly, everything appears to be important; there is a loss of neutrality and sense of proportion.
The new findings highlight sleep's vital role in maintaining good emotional balance and promoting mental health.
The researchers are currently examining how sleep interventions, mostly focusing on REM sleep, may help decrease the emotional dysregulation seen in anxiety, depression and traumatic stress disorders.
Research published recently in Medical News Today suggested that people might not need more than 6.5 hours' sleep a night.