Conscious Dreams Trigger Complex Connections in the Brain

Conscious (lucid) dreams - a rare condition where the sleeper is aware that they are seeing sleep - activate the brain in a way that is different from both normal sleep and wakefulness.

A new study published in The Journal of Neuroscience maps with unprecedented precision the neural activity underlying conscious dreaming.

Lucid dreaming occurs when a person realizes that he or she is dreaming and sometimes even controls the content of the dream. Despite its vividness and exciting nature, this condition is neurologically complex and is still poorly understood.

previous studies have suggested possible brain markers of lucid dreaming, but results have often been inconsistent. Many have used small samples and lacked standardized methods for clearing interfering cues such as eye movements during rapid eye movement (REM) sleep. A team led by Chagatai Demirel from Radboud University Medical Center has attempted to overcome these limitations.

"I'm writing my PhD thesis, which is nearing completion, and this project represents the largest chapter of my work," Demirel explains. "Lucid dreaming feels like a strange crack in reality - a moment when you can observe your mind from within and perhaps even take control of it, even when nothing else seems truly available to understand. This paradox - being awake inside a dream - fascinated me."

Over time, this existential curiosity evolved into a scientific endeavor for Chagatai Demirel. "Unconvincing results regarding electrophysiological correlates in several studies using single EEG datasets with small samples emphasized the need for clarification in this area, in particular by mega-analysis of EEG combining different datasets," he says.

The researchers collected a large dataset from several laboratories in the Netherlands, Germany, Brazil and the United States, resulting in a final sample of 26 "conscious dreamers" who provided a total of 43 usable sleep recordings. These included both low-density and high-density EEG recordings with 128 electrodes monitoring electrical activity across the scalp.

Participants were instructed to perform a specific sequence of eye movements (left-right-left-right-right) as soon as they realized they were dreaming. This standardized cue allowed the researchers to pinpoint the exact moment of lucidity onset.

An important innovation in the study was the development of a multi-stage preprocessing system to clean the EEG data. This was necessary because spontaneous and voluntary eye movements during REM sleep can produce signals that mimic brain activity, especially in the gamma frequency range (30-45 Hz).

The team implemented methods for detecting and removing these saccadic signals that worked even on low-density EEG units. This preprocessing ensured that the signals being analyzed truly reflected neural activity and not muscle movements or other noise.

The researchers then compared brain activity during lucid REM sleep with activity during normal REM sleep and quiet wakefulness. The comparison used both broad bandwidth analysis and more advanced methods measuring brain signal complexity and functional connectivity.

They found that conscious dreams have a distinct neural profile. Although some characteristics are the same as normal REM sleep, such as lower alpha activity and higher delta activity compared to wakefulness, other features distinguish conscious dreams.

One of the key findings was a decrease in theta and beta band power in certain brain regions during lucid dreaming, particularly in the posterior and right temporoparietal regions of the brain. These areas are involved in attention and self-awareness, suggesting that lucid dreaming may engage neural circuits similar to those used during reflection or metacognitive thinking.

At the same time, the researchers observed increased gamma activity - especially in the 30-36 Hz range - at the moment when a sleeping person began to become "conscious." This activity was most pronounced in the precuneus and prefrontal cortex, areas associated with consciousness and internal control.

Functional connectivity analysis showed that lucid dreaming was associated with greater long-range connectivity between brain regions, especially in the alpha and gamma bands. These patterns engaged brain regions known to support sensory integration, internal attention, and memory - functions likely involved in recognizing and maintaining lucidity in dreams.

Notably, alpha connectivity during conscious dreams formed a network involving the superior temporal and superior frontal gyrus, suggesting coordination between auditory, sensory, and executive brain function.

Analysis of signal complexity also distinguished conscious dreams from other sleep states. Metrics such as Lempel-Ziv complexity and entropy, which quantify the unpredictability or saturation of brain signals, were higher in lucid dreaming than in normal REM sleep.

However, these scores were still lower than in the waking state. This suggests that conscious dreams represent an intermediate state of consciousness - more organized and self-conscious than normal sleep, but still different from wakefulness.

"We did not set ourselves any specific objectives (there is no null hypothesis in this project), as this is almost entirely a research endeavor involving combining large datasets from different labs," says Demirel. "But what captivated us most were the results of the source-level analyses (cortical assessment), which are different from the more traditional sensor-level EEG analyses that we also applied. The results of power spectral density (PSD) analyses of EEG at the sensor level during lucid dreaming resembled REM sleep in a statistical sense. However, source-level results revealed increased alpha connectivity during lucid dreaming, which lies between REM-sleep and wakefulness. There is evidence in the literature of alpha-related changes in alpha connectivity associated with psychedelics."

The researchers also examined how brain activity changed in the moments before and after conscious dreamers signaled their awareness with eye movements. Within seconds of this signaling, there was a spike in gamma activity, as well as a large-scale increase in connectivity in the cerebral cortex.

These changes began just before the eye movement signal, suggesting that the brain is preparing for awareness even before the sleeper reports it. These moments may reflect the emergence of self-awareness from the unconscious sleep state.

"The gamma-band activation in the precuneus at the onset of ocular lucidity signaling was a rather unexpected finding," says Demirel. "Bearing in mind that this activation occurs relative to baseline in temporal proximity to onset, it provides potentially compelling data indicating that the brain may be modeling its own reality, reflecting self-referential awareness and possibly motor awareness. This can be interpreted as a potential sensory awakening in a simulated reality."

This study sheds light on the neural mechanisms underlying conscious dreaming by addressing previous methodological challenges and utilizing sensor- and source-level analysis.

By tracking both spectral activity and functional connectivity, researchers are providing a better understanding of how the brain maintains self-awareness in sleep. That said, several open questions remain. Conscious dreams remain difficult to induce under experimental conditions, so researchers often rely on natural occurrences.

The content of dreams also varied widely between participants and sessions, making it difficult to isolate the aspects of the experience most responsible for the observed brain patterns. The study also relied on EEG, which has limited spatial resolution and cannot definitively rule out the influence of residual artifacts - especially in the high-frequency bands where eye movements are most disruptive. Future studies using techniques such as fMRI or intracranial recording could help address these issues.

"The rarity of high-density EEG combined with fMRI data or the lack of magnetoencephalography (MEG) data on lucid dreaming presents a serious limitation for making volumetric assessments of deep brain structures," says Demirel. "Although interesting patterns can be captured at the source level, we had to limit our analysis to cortical assessments. Although we can detect the onset of lucid dreaming from eye signals via electrooculogram (EOG), the actual experience probably starts earlier, and we still don't know exactly when lucid dreaming occurs."

Limitations define the goals. Demirel is now working on developing deeper mathematical models for decoding EEG patterns and improving the sensitivity to phase shifts in decoding non-stationary states.

"Bearing in mind that conscious dreams appear to be a transient brain state, the methodology needs to be revised to distinguish them from stationary signals. This might allow a more accurate segmentation of the lucid state. I also see lucid dreaming as a tool to develop methods that may eventually help redefine the dynamics of sleep and wakefulness, which would also indirectly support research on disorders of consciousness," he says.

"I am just happy that the study is finally published after several years of very grueling work that, at times, seemed like it would never end," Demirel added. "I am very happy to finally share these results with the public."