A 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 of utmost importance for the healthy functioning of our brain and body. Studies have shown that a lack of quality sleep can hinder our ability to regulate our thoughts and emotions and have consequences for our behavior. One of these consequences can be increased aggression.
Although several studies have shown a link between poor sleep and aggressive behavior, the direction of this link remains unclear: sleeps poorly, in fact cause aggressive behavior? Study authors Haobo Zhang and Xu Lei conducted a longitudinal study to answer this question. Through neuroimaging data, they also explored the potential brain mechanism responsible for the relationship between sleep and aggression.
“Since sleep plays an important role in individuals’ physical and mental health, we set out to uncover the causal relationship and mechanisms between sleep quality and aggressive behavior to raise public awareness of the importance of sleep,” said Lei, a 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 from Chongqing, China. They focused on data collected at two time points separated by two years. For the current analysis, the sample consisted of approximately 450 students between the ages of 16 and 26.
At both time points, participants completed an assessment of their subjective sleep quality in the past month, and a measure of aggression that included the subdimensions of hostility, physical aggression, impulsivity, and anger. Students also underwent functional magnetic resonance imaging (fMRI) to measure their brain activity.
To study the relationship between students’ subjective sleep quality and aggression over time, the researchers used a statistical method called cross-lagged panel analysis. This analysis showed that sleep quality at time 1 had a significant effect on aggression at time 2. Aggression, on the other hand, did not significantly affect sleep quality.
“Some researchers have suggested that high levels of aggressive behavior may also contribute to poor sleep, but our findings do not support such a view,” Lei told PsyPost. “This seems to suggest that the physiological effects of aggressive behavior are transient, which should be explored in future studies.”
Importantly, these findings provide preliminary evidence of a causal relationship, with poor sleep causing increased aggression. To better understand this relationship, the researchers tested the associations between sleep quality and each of the four subdimensions of aggression. This showed that poorer 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 affect interpersonal interactions,” Lei told PsyPost. “It is therefore important that people make a conscious effort to get enough and good quality sleep.”
The researchers also compared the students’ sleep and aggression scores to their spontaneous brain activity, as measured by their resting fMRI activity. These results showed that poorer sleep quality and increased aggression were associated with weaker activity in certain brain regions, namely 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 poorer sleep quality and higher aggression were associated with stronger activity in the left and right dorsolateral prefrontal cortex, a brain region involved in emotion regulation.
There are several proposed explanations for why poor sleep might increase aggression. Since poorer sleep only predicted greater hostility and not the other dimensions of aggression, the authors say their findings are most consistent 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 one’s behavior as hostile then encourages aggressive behavior.
A notable limitation was that the study used self-report measures of both sleep quality and aggression. Nevertheless, the study adds to current research by revealing evidence of a causal relationship between sleep quality and aggression. The findings 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,” is authored by Haobo Zhang and Xu Lei.