Summary: Researchers uncovered a metabolic paradox within rapid eye movement (REM) sleep, demonstrating that while overall brain blood volume and energy supplies rise during dreaming, neuronal energy levels drop.
The study monitored real-time brain metabolism in sleeping mice using wide-field fluorescence imaging through a transparent skull preparation. The team tracked blood volume as a marker of fuel delivery, astrocytic pyruvate as a metabolic intermediary, and adenosine triphosphate (ATP) inside neurons.
The researchers observed that approximately 50 seconds before REM sleep onset, blood volume begins rising in the posterior cortex before spreading anteriorly, followed by an increase in astrocytic pyruvate. However, despite this heightened supply, neuronal ATP levels decline during REM sleep, suggesting that heavy memory consolidation and circuit reorganization consume energy faster than the blood supply can replenish it.
Key Facts
- Pre-REM Vascular Surge: Brain blood volume begins increasing approximately 50 seconds before formal REM sleep onset, originating in the posterior cortex and moving forward in a large-scale wave of metabolic preparation.
- Astrocytic Pyruvate Elevation: Following REM sleep onset, astrocytic pyruvate levels rise, indicating increased glucose utilization and heightened glycolytic throughput within support cells.
- Neuronal ATP Paradox: Despite elevated blood delivery and astrocytic pyruvate availability, intracellular neuronal ATP drops sharply during REM sleep, revealing an energy deficit driven by high metabolic consumption.
- Predictive Delta-Theta Dynamics: During non-REM sleep, subtle theta-band neuronal activity fluctuations predict localized blood volume changes several seconds in advance, showing tight neurovascular coupling.
- Mechanistic Cause of ATP Depletion: The drop in neuronal ATP likely stems from high energy costs associated with hippocampal-cortical communication, synaptic reorganization, and memory consolidation occurring during vivid dreaming states.
Source: Tohoku University
Our brain demands a lot of energy compared to our other organs. However, it can also make do when energy supplies are sparse, flexibly performing information processing using what is available. How the brain resourcefully allocates this limited energy across internal states remains a key question in neuroscience.
Sleep provides a useful window to the answer of this question. Although sleep is associated with rest, the brain remains highly active. This is especially true during rapid eye movement (REM) sleep, the stage closely linked to dreaming and memory processing. REM sleep is sometimes called “paradoxical sleep” because the body is largely still while the brain shows wake-like activity.
Researchers at Tohoku University have now uncovered another paradox within REM sleep: while energy supply to the dreaming brain appears to rise, the energy molecule directly used by neurons falls.
The findings were published in Communications Biology on July 27, 2026.
“Ever felt exhausted after a vivid dream?” asks Professor Ko Matsui of Tohoku University. “Sleep may appear peaceful, but the brain is highly active – especially when dreaming. We were intrigued by this paradox, and wanted to look into the scientific basis behind why dreaming is somehow tiring.”
To get a better understanding, the team kept the mouse skull transparent using a UV-curable resin, allowing them to observe the brain during natural sleep. With wide-field fluorescence imaging, they monitored brain blood volume fluctuations as an indicator of “fuel” supply, neuronal ATP as the energy molecule that powers neurons, and astrocytic pyruvate as a key molecule connecting blood-derived glucose to brain energy metabolism.
Non-REM sleep is best known for strong neuronal activity in the delta-band frequency, but subtle theta-band fluctuations are also present. The researchers found that these theta-band fluctuations could predict brain blood volume changes several seconds later, suggesting that the sleeping brain adjusts vascular dynamics to ongoing neuronal activity and metabolic demand.
The transition from non-REM sleep into REM sleep showed a different pattern. About 50 seconds before the classically defined onset of REM sleep, brain blood volume began to rise. This increase started in the posterior cortex and spread forward, suggesting a large-scale metabolic preparation process.
After REM sleep began, astrocytic pyruvate also increased, consistent with enhanced substrate availability or elevated astrocytic glycolytic activity. Paradoxically, however, neuronal ATP decreased.
Several mechanisms may explain the ATP decrease. Neurons may consume large amounts of ATP during REM sleep to support memory-related synaptic reorganization, hippocampal-cortical communication, or large-scale circuit transitions. Alternatively, metabolic transfer from astrocytes to neurons may be altered, or mitochondrial ATP production may shift.
The research also points toward a broader principle of biological computation. Unlike conventional computers, animal brains operate under strict metabolic constraints. Rather than distributing energy uniformly, the brain may reroute energy depending on behavioral state, memory demand, and internal needs.
“Understanding how the brain balances energy supply and consumption may help explain what makes biological intelligence so efficient,” explains lead investigator Yusuke Takahashi. “REM sleep gives us a natural example of how the brain reorganizes its energy economy to support complex internal processing.”
Sleep is a vital function that can help consolidate memories and keep us mentally sharp the next day. These research findings about energy and sleep are a crucial step forward to helping us understand the science behind sleep, and how a good night’s rest is not just important for our bodies – but our minds too.
Key Questions Answered:
A: REM sleep is traditionally called paradoxical sleep because while the physical body remains immobilized in muscle atonia, the brain exhibits high-frequency, wake-like electrical activity. This study reveals a second paradox: even though the brain increases blood flow and fuel supply during REM sleep, the energy molecule directly powering neurons (ATP) decreases significantly.
A: Neurons consume immense amounts of energy during REM sleep to drive memory consolidation, reorganizing synaptic connections, and communicating across hippocampal-cortical networks. The rapid decline in ATP indicates that neuronal energy expenditure during dreaming processing exceeds the rate of metabolic delivery and mitochondrial ATP regeneration.
A: The Tohoku University team created a transparent skull window in mice using UV-curable resin. Using real-time, wide-field fluorescence imaging, they simultaneously measured fluorescent biosensors for neuronal ATP, astrocytic pyruvate, and intrinsic optical signals for cerebral blood volume while the animals progressed naturally through non-REM and REM sleep cycles.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this neurodevelopment and mental health research news
Author: Public Relations Office
Source: Tohoku University
Contact: Public Relations Office – Tohoku University
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Energy paradox in REM sleep: balancing supply and consumption in brain metabolism” by Yusuke Takahashi, Yoko Ikoma & Ko Matsui. Communications Biology
DOI:10.1038/s42003-026-10646-6
Abstract
Energy paradox in REM sleep: balancing supply and consumption in brain metabolism
The brain’s capacity for information processing depends on precisely regulated energy dynamics. Yet how metabolic supply adapts to shifting computational demands across brain states remains unclear. Using wide-field fluorescence imaging through the intact skull of live mice, we simultaneously monitored brain blood volume (BBV), astrocytic pyruvate, and neuronal ATP levels during natural sleep.
We found that large-scale metabolic dynamics are coupled to neuronal activity but reorganize in a state-dependent manner. During non-rapid eye movement (NREM) sleep, theta-band electrocorticogram (ECoG) activity predicted subsequent blood volume changes, accompanied by rapid anterior-to-posterior vascular waves.
In contrast, REM sleep was marked by a pronounced increase in BBV, originating in the posterior cortex and slowly propagating across the brain. This was accompanied by elevated astrocytic pyruvate; paradoxically, however, neuronal ATP levels declined sharply.
These findings reveal a dynamic interplay among neurons, astrocytes, and the vasculature, suggesting that distinct energy-allocation strategies underlie the brain’s computational flexibility.
