Woke up exhausted after a whole night? The study that explains why

A new study from Tohoku University in Japan, published in Communications Biology, reveals a metabolic paradox during REM sleep: blood supply to the brain increases, but the energy available directly to nerve cells actually decreases. The researchers identified that the brain prepares for dreaming about 50 seconds before the stage begins, and the findings may explain why vivid dreams leave a feeling of fatigue.

A new study from Tohoku University in Japan, published in the journal Communications Biology, reveals a metabolic paradox that occurs during REM (rapid eye movement) sleep, the stage linked to dreaming and memory processing. The researchers found that while blood supply to the brain increases during dreaming, the energy available directly to nerve cells actually decreases. This contradiction, referred to in the article as "another paradox," led the team to investigate the physiological basis of the activity. The study identified a unique pattern: brain blood volume began to rise about 50 seconds before the official onset of the REM stage, starting in the posterior region of the cerebral cortex and moving forward. According to the researchers, this may indicate a widespread metabolic preparation of the brain for the dreaming stage even before it begins. The decrease in energy available to nerve cells during dreaming may stem from increased energy consumption for reorganizing neural connections related to memory, heightened communication between the hippocampus and the cerebral cortex, or extensive transitions between neural circuits. The study adds a layer to understanding the importance of sleep for mental function and explains why particularly vivid dreams may leave a feeling of fatigue.