A new study by Mass General Brigham reveals how brain activity, energy use and blood flow interact during sleep, shedding light on sleep’s role in brain health and disease prevention.
A team of researchers from Mass General Brigham has unlocked new insights into the brain’s behavior as people fall asleep, uncovering complex changes in brain activity, energy usage and blood flow.
The findings, published in Nature Communications, explore how different areas of the brain transition from wakefulness to non-rapid eye movement (NREM) sleep, a critical phase for physical health, brain function and disease prevention.
Using advanced imaging techniques, the study reveals that during NREM sleep, regions of the brain responsible for movement and sensory input remain active and continue to consume energy, while areas tied to thinking, memory and self-reflection become less active. The blood flow to these areas also shifts, becoming more dynamic.
“This research helps explain how the brain stays responsive to the outside world even as awareness fades during sleep,” corresponding author Jingyuan Chen, an assistant investigator in the Athinoula A. Martinos Center for Biomedical Imaging at Massachusetts General Hospital, a founding member of the Mass General Brigham healthcare system, said in a news release.
By implementing a tri-modal EEG-PET-MRI approach, combining electroencephalography (EEG) to monitor brain waves, functional MRI (fMRI) to track blood flow, and functional PET (fPET)-FDG to observe glucose metabolism, the investigation analyzed the brains of 23 healthy adults during brief nap sessions.
The researchers discovered that as sleep deepens, both energy consumption and metabolism decline, while blood flow becomes more dynamic — particularly in sensory regions that remain relatively active. Meanwhile, higher-order cognitive networks become less active, and the flow of cerebrospinal fluid increases. Collectively, these observations suggest that sleep facilitates the brain’s waste-clearing processes while preserving responsiveness to sensory signals that might prompt awakening.
Chen highlighted that the discovery could offer “new insights into the mechanisms of neurological and sleep-related diseases,” emphasizing the relevancy of understanding these fundamental processes.
The study’s findings validate the critical role of NREM sleep in maintaining brain health. NREM sleep is widely recognized for its regenerative properties, yet its detailed mechanisms and long-term impacts have been elusive.
The researchers emphasize that future research should involve larger and more diverse participant groups, along with longer and more comprehensive sleep recordings. They also plan to employ more precise techniques to measure brain metabolism and to more accurately differentiate between stages of sleep.
Source: Mass General Brigham