Scientists may have finally unlocked the secret behind why we have angry dreams through a study.
Experts found an imbalance between two regions of the brain found on both the left and right sides is to blame for the unsettling nightmares.
A tell-tale sign is an effect called frontal alpha asymmetry, where a specific type of brain activity is higher in one side of the brain.
The findings come from studies of 17 healthy volunteers who had their brains scanned before, during and after sleep.
Researchers from the UK, Finland and Sweden looked at how our brains regulate emotions like anger and curiosity when we are dreaming at night.
Study participants spent two nights in a sleep laboratory, where researchers took electroencephalographic (or EEG) recordings of their brain activity for short periods before, during and after slumber.
Among the volunteers were 7 men and 10 women, all of whom were healthy.
Experts found that participants who experienced less brain activity in their right frontal cortex rather than its left-hand counterpart while they were awake and during REM sleep experienced more anger in their dreams.
‘It has been shown that expressing anger is related to relatively greater left [frontal activity], whereas controlling anger is related to relatively greater right frontal activity,’ said lead author Pilleriin Sikka, a researcher at University of Turku in Finland.
‘Anger was experienced in 41 percent of dreams, interest in 88 percent of dreams.
‘Participants experienced more anger in dreams than during the evening wakefulness, whereas the evening and morning anger ratings did not differ.’
Experts looked out for signs of the participants reaching rapid eye movement (REM) sleep.
This cycle of our sleep patterns is characterised by rapid eye movements, a faster pulse, quicker breathing, bodily movement and more dreaming.
Researchers woke participants after they had experienced a five-minute bout of REM sleep.
They then asked the sleepers to describe the dreams they had been having and rate the emotions they had experienced within them.
From these dream reports, the experts labelled the emotional states of the participants dreams – such as ‘angry’, or ‘interest’.
The only other emotional dream state that had a significant correlation with frontal alpha asymmetry during REM sleep was one closely related to anger – distrust or suspicion.
The findings suggest that this pattern of brain activity is a good way of predicting how people control their emotions.
Previous studies have linked frontal alpha asymmetry with both anger and general self-regulation while awake.
The new findings may help researchers to understand and potentially mitigate the emotional content of nightmares.
These can be a distressing symptom of many mental and sleep disorders, including post-traumatic stress disorder.
The full findings of the study were published in the journal JNeurosci.