New research provides further evidence that insomnia is characterized by brain hyperarousal, even when controlling for symptoms of depression and anxiety.
The study used electroencephalography (EEG) to measure daytime brain activity in patients with insomnia disorder compared to healthy controls.
Key findings:
- Patients with insomnia disorder showed increased high-frequency beta and gamma brain wave activity compared to controls, indicating hyperarousal of the brain.
- Beta wave activity positively correlated with insomnia severity and predicted insomnia symptoms even after accounting for anxiety and depression.
- The hyperarousal was widespread across the brain rather than localized to specific regions.
- The hyperarousal was observed during daytime waking EEG, not just during sleep, supporting the theory that insomnia involves 24-hour hyperarousal.
Source: Clinical Psychopharmacology & Neuroscience 2023
Insomnia Disorder Basics
Insomnia disorder involves:
- Difficulty initiating or maintaining sleep
- Impairment in daytime functioning due to poor sleep
- Occurring despite adequate opportunity for sleep
Insomnia is highly prevalent, affecting 10-15% of adults, and is linked to impaired cognitive function, increased risk of cardiovascular disease, and psychiatric disorders like depression and anxiety.
The Hyperarousal Model of Insomnia
The hyperarousal model proposes that insomnia is characterized by hyperarousal of the central nervous system that is present 24 hours a day.
This state of hyperarousal interferes with sleep initiation and maintenance.
The hyperarousal model is supported by evidence that people with insomnia show:
- Increased high-frequency EEG activity during non-REM and REM sleep
- Higher waking EEG frequencies
- Elevated heart rate, body temperature, cerebral metabolism during sleep
- Heightened cortisol secretion
Critically, most prior studies focus on sleep-related hyperarousal.
This new study examined daytime waking EEG as further evidence for 24-hour hyperarousal in insomnia.
Evaluating Hyperarousal in Insomniacs (Study)
Researchers conducted a study to evaluate hyperarousal in people with insomnia.
Included below are some of the specific study details:
- 107 participants
- 58 with insomnia disorder, 49 healthy controls
- 5 minute daytime waking EEG recorded (eyes closed)
- Depression and anxiety symptoms measured with clinical scales
- Insomnia severity measured with Pittsburgh Sleep Quality Index (PSQI)
Results: Insomnia & Brain Hyperarousal
Beta and Gamma Power:
- Those with insomnia showed higher beta (12-30Hz) and gamma (30-40Hz) power in the waking EEG compared to controls.
- Beta and gamma power indicate brain activation and wakefulness.
- The elevated power was widespread across frontal, temporal, centro-parietal, and occipital regions.
Beta Waves Predict Insomnia Severity:
- Across all participants, higher beta brain waves correlated with more severe insomnia symptoms on the PSQI.
- Beta power predicted insomnia severity even after controlling for anxiety and depression symptoms.
- This shows beta hyperarousal is linked to insomnia independently of mood symptoms.
Hyperarousal Model: Supporting Evidence
The heightened beta and gamma power during waking EEG provides further evidence that insomnia involves hyperarousal of brain activity.
This hyperarousal state is present during daytime rest, not just during sleep.
Beta hyperarousal specifically relates to insomnia severity, not just depression/anxiety symptoms.
Together these results support the view that insomnia involves 24-hour hyperarousal of the brain.
Limitations & Future Directions
As a cross-sectional study, this cannot determine cause-and-effect relationships between brain activity and insomnia.
Other measurements like polysomnography would provide additional insights into sleep-related hyperarousal.
Understanding connections between the hyperarousal-related brain regions could elucidate the mechanisms.
Studying patients over time could reveal more about hyperarousal precipitating and perpetuating insomnia.
Hyperarousal Model of Insomnia Supported
This study provides some of the most robust evidence to date for the hyperarousal model of insomnia.
The findings suggest that hyperarousal, as measured by beta EEG power, is an intrinsic feature of insomnia rather than just a byproduct of mood disturbances.
Daytime waking EEG could be a convenient biomarker for investigating insomnia mechanisms and effects of treatments.
Targeting brain hyperarousal may be key for developing new insomnia therapies.
Uncovering the origins and functions of hyperarousal in insomnia remains an important goal for future research.
References
- Study: Hyperarousal-state of insomnia disorder in wake-resting state quantitative electroencephalography
- Authors: Gyutae Jang et al. (2023)
