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A study finds poor sleep quality increases aggression, possibly by affecting emotional cognition

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Lack of quality sleep can cause aggressive behavior, according to recent longitudinal findings published in the journal Biological Psychology. Brain imaging data revealed that the effect may be related to reduced activity in the prefrontal cortex and increased activity in the limbic regions.

Good sleep is essential for the proper functioning of our brain and our body. Studies have shown that a lack of quality sleep can hamper our ability to regulate our thoughts and emotions and impact our behavior. One of these consequences could be increased aggression.

Although several studies have indicated a link between poor sleep and aggressive behavior, the direction of this relationship remains unclear – is poor sleep actually cause aggressive behavior? Study authors Haobo Zhang and Xu Lei conducted a longitudinal study to try to answer this question. Using neuroimaging data, they also explored the potential brain mechanism responsible for the relationship between sleep and aggression.

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“As sleep plays an important role in the physical and mental health of individuals, we thought of uncovering the causal relationship and mechanisms between sleep quality and aggressive behavior in order to raise public awareness of the importance of sleep”, said Lei, professor, and director of the Sleep and NeuroImage Center at Southwest University in China.

Zhang and Lei obtained data from the Behavioral Brain Research Project of Chinese Personality (BBP), an ongoing study of undergraduate students in Chongqing, China. They focused on data collected at two points two years apart. For the current analysis, the sample consisted of approximately 450 students aged 16-26.

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At both time points, participants completed an assessment of the subjective quality of their sleep over the previous month and a measure of aggression that included the subdimensions of hostility, physical aggression, impulsivity, and anger. The students also underwent functional magnetic resonance imaging (fMRI) to measure their brain activity.

To investigate the relationship between students’ subjective quality of sleep and aggression over time, the researchers used a statistical method called cross-lagged panel analysis. This analysis revealed that sleep quality at time 1 had a significant effect on aggression at time 2. In contrast, aggression had no significant impact on sleep quality.

“Some researchers have suggested that high levels of aggressive behavior may also contribute to poor quality sleep, but our results do not support such an opinion,” Lei told PsyPost. “This seems to suggest that the physiological effects of aggressive behavior are temporary, which should be examined in future studies.”

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Importantly, these results offer tentative evidence for a causal relationship, that poor sleep causes increased aggression. To better understand this relationship, the researchers tested associations between sleep quality and each of the four sub-dimensions of aggression. This revealed that poor sleep quality was only a significant predictor of increased hostility.

“Sleep is extremely important to humans, and poor sleep can increase hostility in individuals, which can damage their interpersonal relationships and negatively impact interpersonal interactions,” Lei told PsyPost. “So it’s important that people make a conscious effort to get enough, good quality sleep.”

The researchers also compared the students’ sleep and aggression scores to their spontaneous brain activity, as measured via their resting-state fMRI activity. These results revealed that poor sleep quality and increased aggression were linked to lower activity in certain areas of the brain, notably in the limbic or frontal regions.

The authors say this may suggest that lower sleep quality led to deficits in emotional cognition – the ability to correctly interpret the emotions of others. The results also revealed that poor sleep quality and higher aggression were linked to higher activity in the left and right dorsolateral prefrontal cortex, an area of ​​the brain involved in emotion regulation.

There are several explanations offered as to why poor sleep might increase aggression. Since poor sleep only predicted increased hostility and not the other dimensions of aggression, the authors say their results align better with the cognitive pathway of the general aggression model. This interpretation suggests that poor sleep makes people more likely to interpret the behavior of others in a negative light. This greater tendency to attribute someone’s behavior as hostile than encourages aggressive behavior.

A notable limitation was that the study used self-report measures of sleep quality and aggression. Nonetheless, the study adds to current research by revealing evidence of a causal relationship between sleep quality and aggression. The results further suggest that poor sleep may promote aggression by affecting emotional cognition.

The study, “Effect of Subjective Sleep Quality on Aggression: A Two-Year Longitudinal and fMRI Pilot Study,” was authored by Haobo Zhang and Xu Lei.

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