New research provides evidence that people suffering from nightmare disorder have increased responsiveness to internal sensory signals during the “dreaming” stage of sleep. The findings have been published in the journal NeuroImage: Clinical.

“We have been fascinated by the nature of dreams since the birth of humankind. Only recently have we started unraveling how they are being produced in the brain and still, more research is needed to characterize the neural correlates of specific dream contents, or even a potential function of dreaming,” said study author Lampros Perogamvros, a psychiatrist and senior researcher at the University Hospitals of Geneva and University of Geneva.

“The pathophysiology and neural correlates of nightmare disorder, which is characterized by frequent dreams with strong negative emotions, remain largely unknown and their investigation was the main aim of this study.”

The study used electroencephalography (EEG) to examine the brain activity of 11 patients with nightmare disorder and 11 matched controls during wakefulness and sleep. The researchers were particularly interested in a brain signal known as the heartbeat evoked potential (HEP).

The researchers found that patients with nightmare disorder had a stronger HEP response during rapid eye movement (REM) sleep compared to the control group. During this stage of sleep, the eyes move rapidly and there is increased brain activity. REM sleep is also the stage when dreaming occurs.

“We found that, compared to healthy participants, patients with nightmare disorder had increased amplitude of the heartbeat-evoked potential, which represents the response of the brain to our heartbeat. This difference was found only in REM sleep and not in non-REM sleep or wakefulness, indicating that nightmares are essentially a REM pathology,” Perogamvros told PsyPost.

Interestingly, the increased HEP amplitude in nightmare patients was observed even after excluding patients who had reported having a nightmare when the study was conducted.

“In general, the heartbeat-evoked potential reflects internal sensory processing (interoception) and its amplitude is increased during states of high emotional arousal. Increased amplitude of this potential in nightmare disorder during REM sleep indicates that elevated emotional and sensory processing participates in the pathophysiology of this sleep disorder,” Perogamvros explained.

“Indeed, this increase was found in a frontal region, finding which is consistent with a stronger activation of frontal brain structures (e.g. anterior cingulate cortex) implicated in emotional processing and negative emotions during the period of sleep associated with nightmares (REM sleep).”

Future research could benefit from larger sample sizes and EEG with better spatial resolution. “Studies using high-density electroencephalography (>64 electrodes) would increase the localization accuracy of the main finding,” Perogamvros said.

The study, “Increased heartbeat-evoked potential during REM sleep in nightmare disorder“, was authored by Lampros Perogamvros, Hyeong-Dong Park, Laurence Bayer, Aurore A. Perrault, Olaf Blanke, and Sophie Schwartz.