Berkeley, CA, USA. It has long been assumed that sleep deprivation can play havoc with our emotions. Now we know that when the amygdala, a crucial structure in the brain, goes into overdrive it shuts down the prefrontal cortex.

A new study from Harvard Medical School and the University of California, Berkeley is the first to explain, at the neural level, what seems to be a universal phenomenon: that sleep loss leads to emotionally irrational behavior.

This is notably apparent in soldiers in combat zones, medical residents and even new parents.

The findings might also offer some insight into the clinical connection between sleep disruptions and psychiatric disorders. In the first neural investigation into what happens to the emotional brain without sleep, results from a brain imaging study suggest that while a good night's rest can regulate your mood and help you cope with the next day's emotional challenges, sleep deprivation does the opposite by excessively boosting the part of the brain most closely connected to depression, anxiety and other psychiatric disorders.

Without sleep, the emotional centers of the brain dramatically overreact to negative experiences. The reason for that hyperactive emotional response in sleep-deprived people stems from a shutdown of the prefrontal lobe — a region that normally keeps emotions under control.

The amygdala (Gr. almond) is a small structure in the medial temporal lobe of the brain, a few inches from either ear. 

 

 

The left and right amygdalae are not physically identical. Neuroimaging studies suggest that the right amygdala has a larger volume than the left. Additionally, the two are functionally asymmetrical as well.

 

Recent research points to the circuits, not just the structure. The nerves coursing through the amygdala connect it to a number of important brain centers, including the neocortex and visual cortex.

 

Specifically, the left amygdala appears to be consistently activated in response to negative, withdrawal-related stimuli. The right amygdala seems to be involved in autonomic responses (heart rate, skin responses, blood pressure, etc.).

 

Amygdala activation can be driven by one's own emotional experiences. It has long been linked with a person's mental and emotional state, playing a critical role in several emotional behaviors.

 

These include the evaluation of and response to emotionally salient information, anxiety disorders, depression, and the arousal-related components of drug abuse.

 

The fact that the amygdala influences diverse emotional responses suggests that it serves an important emotional function. It likely influences perception and arousal responses before higher-level, cognitive analysis of the stimuli.

"Emotionally, you're not on a level playing field," Walker added. That is because the amygdala, the region of the brain that alerts the body to protect itself in times of danger, goes into overdrive on no sleep, according to the study.

This consequently shuts down the prefrontal cortex, which commands logical reasoning, and thus prevents the release of chemicals needed to calm down the fight-or-flight reflex.

If, for example, the amygdala reacts strongly to a violent movie, the prefrontal cortex lets the brain know that the scene is make-believe and to settle down. But instead of connecting to the prefrontal cortex, the brain on no sleep connects to the locus coeruleus, the oldest part of the brain which releases noradrenalin to ward off imminent threats to survival, posing a volatile mix, according to the study.

The study's findings lay 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.

Scientists have known that sleep deprivation impairs a range of bodily functions, including the immune system and metabolism, as well as brain processes, such as learning and memory, the researchers explained. Yet, evidence for the role of sleep in governing our emotional brain state had remained surprisingly scarce, they noted.

"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 said. "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."

Using functioning Magnetic Resonance Imaging (fMRI), Walker and his team found that the amygdala, which is also a key to processing emotions, became hyperactive in response to negative visual stimuli - mutilated bodies, children with tumors and other gory images - in study participants who stayed awake for 35 hours straight. Conversely, brain scans of those who got a full night's sleep in their own beds showed normal activity in the amygdala.

“We had predicted a potential increase in the emotional reaction from the brain [in people deprived of sleep], but the size of the increase truly surprised us,” Walker said of the study’s findings. "The emotional centers of the brain were over 60 percent more reactive under conditions of sleep deprivation than in subjects who had obtained a normal night of sleep."

The team studied 26 healthy participants aged 18 to 30, breaking them into two separate groups, each with equal numbers of males and females. WWalker’s team assigned 26 healthy people to either a sleep-deprivation group — in which participants were kept awake for about 35 hours — or a normal sleep group.

On the following day, the study subjects’ brains were scanned by fMRI, measuring brain activity on the basis of blood flow, while viewing 100 images. The images were at first emotionally neutral, but became increasingly aversive over time.

During the fMRI brain scanning, which was performed at the end of day 2, each was shown 100 images that ranged from neutral to very negative.

Using this emotional gradient, the researchers were able to compare the increase in brain response to the increasingly negative pictures.

Since 1998, Walker, an assistant professor of psychology at UC Berkeley and a former sleep researcher at Harvard Medical School, has been studying sleep's impact on memory, learning and brain plasticity.

During his research, he was struck with the consistency of how graduate students in his studies would turn from affable, rational beings into what he called "emotional JELL-O" after a night without sleep. He and his assistants searched for research that would explain the effect of sleep deprivation on the emotional brain and found none, although there is countless anecdotal evidence that lack of sleep causes emotional swings.

"You can see it in the reaction of a military combatant soldier dealing with a civilian, a tired mother to a meddlesome toddler, the medical resident to a pushy patient. It's these everyday scenarios that tell us people don't get enough sleep." Walker said.

The body alternates between two different phases of sleep during the night:

• Rapid Eye Movement (REM), when body and brain activity promote dreams, and
  
  
• Non-Rapid Eye Movement (NREM), when the muscles and brain rest.

“This adds to the critical list of sleep’s benefits,” said Walker. “Sleep appears to restore our emotional brain circuits, and in doing so prepares us for the next ay’s challenges and social interactions. Most importantly, this study emonstrates the dangers of not sleeping enough. Sleep deprivation fractures the brain mechanisms that regulate key aspects of our mental health. The bottom line is that sleep is not a luxury that we can optionally choose to take whenever we like. It is a biological necessity, and without it, there is only so far the band will stretch before it snaps, with both cognitive and emotional consequences.”

“While it is early days,” he added, “clinical evidence has shown that some form of sleep disruption is present in almost all psychiatric disorders. These findings may offer new mechanisms as to why, and provide novel insights into how we can understand and even treat these disorders at a brain level.”

"All signs point to sleep doing something for emotional regulation and emotional processing," Walker said. "My job now is to figure out what kind of sleep."

ParticipantsThe researchers include Seung-Schik Yoo, Ferenc A. Jolesz, of the Department of Radiology, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts, USA; Ninad Gujar, Peter Hu, and Matthew P. Walker, of the Sleep and Neuroimaging Laboratory Department of Psychology and Helen Wills Neuroscience Institute, University of California, Berkeley, California, USA.

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