A study looked at the link between "dreamed" and "real" fear. Sleep, and its associated dreams, seems to allow the retreatment and reorganization of emotional information.
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A study1 published in Human Brain Mapping looked at the link between "dreamed" and "real" fear. The links between sleep and emotional processes have been the object of extensive focus. Chronic sleep disruption is perceived to lead to increased aggressiveness; while acute sleep deprivation exacerbates emotional reactions to negative stimuli (by altering prefrontal control of the limbic regions). In addition, depression and post-traumatic stress disorder (PTSD) are associated with sleep disorders (e.g., insomnia and recurring nightmares). Sleep, therefore, seems to allow the retreatment and reorganization of emotional information.
The threat simulation theory of dreaming (TST) postulates that dreams are also used to simulate threat events "offline" to practice threat prevention techniques. A person's emotional story would be replayed in the virtual and safe environment of the dream. This mechanism would promote appropriate behavioral responses in real-life situations.
Are dreams, therefore, a resolution of current emotional distress and/or optimization of emotional responses for the conscious mind? These two theoretical models are based on the premise that the same brain circuits involved during "dreamed" emotions are involved in those experienced during our awake time. For example, anatomical studies have already shown that alteration of the structural integrity of the left amygdala is associated with reduced emotional intensity in dreams.
The use of the high-density electroencephalogram (EEG) has also shown that certain regions of the brain are responsible for the genesis of dreams, and that depending on the more specific content of the dream (perceptions, thoughts, emotions) other regions are also activated. Fear, as felt in a dream, has been clearly dissociated from other, more "social" emotions (embarrassment, excitement, or frustration). Fear’s functioning is distinct: it is a biologically significant and prevalent emotional category.
Swiss and American researchers1 from the University of Geneva (UNIGE), the Geneva University Hospitals (HUG) and the University of Wisconsin focused on answering two questions:
1. Do the emotions linked to fear in dreams engage the same neural circuits as fear during the awake time?
2. Is there a link between the emotions felt in dreams and the brain's reactions to emotional stimuli during the awake time?
To establish these relationships between dreams and functional measures of brain activity, the researchers analyzed the dreams of several people and identified which areas of the brain were activated when they experienced fear in dreams. They used high-density EEGs (hdEEG), functional MRI (fMRI), and analyzed changes in pupil size when aversive stimuli were presented.
"We were particularly interested in fear: which areas of our brain are called upon when we have a bad dream," explained Lampros Perogamvros, a researcher in Professor Sophie Schwartz's 'Sleep and Cognition' laboratory2.
The scientists placed 256 EEG electrodes on 18 people and woke them up several times during the night. Each time they woke up, they had to answer a series of questions such as: "Did you dream? If so, did you feel fear?"
"By analyzing brain activity based on participants' responses, we have identified two brain regions as being responsible for the fear felt in a dream: the insula and the cingulate cortex," explained Perogamvros. The insula is systematically activated when fear is felt. The cingulate cortex plays a role in preparing motor and behavioral reactions in the event of danger.
"For the first time, we have identified the neuronal correlates of fear when we dream and have shown that certain brain regions are activated when fear is felt in awake time or dreaming," said the Geneva-based researcher.
The researchers found that once individuals woke up, the brain areas responsible for controlling emotions were much more effective in managing fear in the situations they faced. The researchers initially gave a dream book to 89 participants. Each morning for a week, participants were asked to describe their dreams from the previous night and identify the emotions they felt, of which fear was one of them.
At the end of the week, the participants were placed in an MRI. "We showed each participant emotionally negative images, such as aggression or distress situations, and neutral images to see which areas of the brain were more active for fear and whether this activation changed according to the emotions in the dreams of the previous week," said Virginie Sterpenich, a researcher in the Department of Fundamental Neurosciences at the Faculty of Medicine, UNIGE.
The researchers focused on brain areas traditionally involved in managing emotions, such as the insula, amygdala, medial prefrontal cortex, and cingulate cortex. "We found that the more fear a person experienced in their dreams, the less active the insula, cingulate and amygdala were when they were confronted with negative images," explained Sterpenich. "In addition, the activity of the medial prefrontal cortex, which is known to inhibit the amygdala in the event of fear, increased in proportion to the number of dreams where fear was felt".
These results demonstrate a very strong link between emotions felt during our sleep and awake time, and support the neuroscientific theory that, during dreams, we simulate frightening situations that prepare us to react to them once awake. "Dreams can be seen as a real training ground for our future reactions and can potentially prepare us to face dangers," insisted Perogamvros.
From these findings, the researchers are hence suggesting that dreams could be new "therapeutic allies" in the treatment of anxiety disorders, and this in itself opens a new myriad of potential research and application areas.
"Bad dreams" are the cause of moderate fear. Nightmares, on the other hand, cause an excessive level of fear that disrupts sleep and has a negative impact on the person who is awake. "We believe that if a certain threshold of fear in a dream is exceeded, the dream loses its beneficial role as an emotional regulator," Perogamvros explained.
Indeed, previous studies have already shown that recurrent nightmares, such as those observed in patients suffering from PTSD, could indicate a failure of the memory's fear extinction function, which normally allows the disappearance of fear by habituation to the stimulus. Patients with nightmares may also be more prone to emotional dysregulation. Conversely, high anxiety during wakefulness may increase the excitability of negatively charged memories during sleep. Such a disruption of emotional regulation during wakefulness and sleep has been proposed as one of the main factors contributing to insomnia.
References:
1. Sterpenich, Virginie & Perogamvros, Lampros & Tononi, Giulio & Schwartz, Sophie. (2019). Fear in dreams and in wakefulness: Evidence for day/night affective homeostasis. Human Brain Mapping. 10.1002/hbm.24843.
2. Department of Fundamental Neurosciences of the Faculty of Medicine of the UNIGE and Head of the Scientific Clinic at the HUG Sleep Medicine Center.