Brain blood flow rises as cellular energy falls during REM sleep

The research group of Graduate Student Yusuke Takahashi, Assistant Professor Yoko Ikoma, and Professor Ko Matsui of Graduate School of Life Sciences at Tohoku University, observed the cerebral cortex in live mice during natural sleep. They revealed that during REM sleep, brain blood volume and pyruvate in astrocytes increase, while ATP in neurons decrease. It has been thought that neuronal energy would increase if blood flow increases, but they found the opposite phenomenon during REM sleep. This is expected to lead to elucidation of the mechanism of memory formation during sleep. The results were published in Communications Biology on July 27.

Sleep is considered to be a form of rest, but the brain processes information depending on the state of sleep. It is believed that the brain constructs dreams and organizes memories particularly during REM sleep. The research group has previously reported large changes in astrocytes (a type of glial cells) and blood volume during REM sleep.

In these developments, the group investigated how metabolic energy is supplied and consumed in the brain during REM sleep. They made the skull of the mouse transparent and observed the cerebral cortex through the skull under a stereomicroscope (wide-area fluorescence imaging). By simultaneously recording electrocorticogram and electromyogram, they successfully analyzed changes from non-REM sleep to REM sleep in a natural state. No large fluctuation was seen during non-REM sleep. Upon entering REM sleep, blood volume increased and in contrast neuronal activity was suppressed, showing a mirror image relationship with blood volume.

Next, they investigated the relationship between the neuronal electrical activity and the fluctuation of blood volume. Theta waves become stronger during REM sleep. During non-REM sleep, on the other hand, theta wave components are less prominent but still present with fluctuations in intensity. Thus, they examined the fluctuations.

The result showed that theta waves correspond well with the blood volume fluctuations after 4-5 seconds. The brain is believed to have a homeostasis maintenance mechanism that regulates the required energy supply according to the neuronal intensity.

Next, they investigated when and in which area of the brain the blood volume fluctuates and found that the blood volume finely fluctuated during non-REM sleep and significantly increased upon transition to REM sleep. Brain blood volume began to increase about 50 seconds before the start of REM sleep as determined by electrocorticogram and electromyogram. This change occurred from the posterior cerebral cortex and spread forward over the course of about 15 seconds. It became clear that the transition from non-REM sleep to REM sleep occurs gradually.

They also investigated how the energy source supplied from blood is used between astrocytes and neurons. Glucose supplied from blood is taken up by astrocyte and broken down via pyruvate into lactate, which is then taken up by neuron and converted to pyruvate, which is taken up by mitochondria to produce ATP. Normally, when a blood vessel-dilating drug is administered, blood volume increases, and pyruvate and ATP increase in astrocytes. During REM sleep, however, blood volume increases but ATP decreases in neurons.

This finding indicates the possibility that the balance between energy supply and consumption changes during REM sleep. Since REM sleep is responsible for high-level information processing, such as memory formation, they speculate that energy consumption may exceed the rate of ATP production.

Journal Information
Publication: Communications Biology
Title: Energy paradox in REM sleep: balancing supply and consumption in brain metabolism
DOI: 10.1038/s42003-026-10646-6