Why Does Sleep Deprivation Make Some People Grumpy? It’s All In The Brain, New Research Suggests

Why do some people get moody if they don’t have enough sleep? Prostock-studio/Shutterstock

Why do some people get moody if they don’t have enough sleep?

It very well may be all in the brain. According to new research from the University of Arizona, the compactness of a type of brain tissue called white matter may influence a person’s temperament when they don’t get enough sleep.

People respond differently to a loss of sleep. Some may become agitated and irritable while others appear to hardly be affected. Previous studies indicate that sleep is vital to cognitive, social, and physical function, can affect our attention span, and even increases anxiety while lowering our ability to manage stress and think positively. A study published earlier this year found that a genetic difference could allow some people to function on less sleep and the effects of a lack of sleep may not be easily reversible. But what makes a sleepy person grumpy?

To determine what makes a person more likely to be moody following sleep deprivation, researchers studied three networks of interaction within the brain: the default-mode (DMN), central executive (CEN), and salience networks. The DMN is believed to be related to dreaming and may help us consolidate memories while asleep while the CEN is action-oriented. On the other hand, the salience network is believed to be responsible for integrating emotional and sensory stimuli and can mediate a switch between the DMN and CEN. Research suggests that interconnectivity between the three may impact psychiatric and neurological disorders.

The salience network is believed to mediate switching between the DMN and CEN. Nekovarova, Fajnerova, Horacek, Spaniel/Wikimedia Commons

Researchers first analyzed the brains of 45 individuals using MRI scans and a specialized technique known as diffusion tensor imaging (DTI). Several days later, study participants returned to the lab and stayed awake overnight while being asked questions regarding their mood every hour between 7.15pm and 11.15 the following morning while the researchers looked at several regions within the brain.

Participants who had greater white matter compactness, insulated fibers that connect the brain cells of gray matter together, were better able to stay positive.

“We found that it is the compactness of white matter that is associated with greater resilience to mood degradation induced by 24 hours of sleep deprivation,” study author Sahil Bajaj told PsyPost. “Characteristics of gray matter do not seem to play a role in sustaining mood degradation following sleep deprivation. Very simply put, people with more compact white matter fibers seemed to be less likely to get ‘moody’ when sleep-deprived.”

However, the researchers are quick to caution that much more research is needed to fully understand how a person’s mood is impacted by a loss of sleep.

“Our study focused on only structural characteristics of the triple-network model and their association with mood-shifts,” wrote the authors in NeuroImage, adding that future work should identify and clarify the causal associations between mood variability and whole-brain functional characteristics.  

Frontal, sagittal, and transverse sectional planes of the human brain as seen by MRI scans. kalewa/Shutterstock
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