Summary: Researchers have identified a metabolic paradox in rapid eye movement (REM) sleep: although brain blood volume and markers of fuel delivery increase during dreaming, the energy molecule used directly by neurons—adenosine triphosphate (ATP)—falls.
Using wide-field fluorescence imaging through a transparent skull window in naturally sleeping mice, the team tracked three simultaneous signals in real time: cerebral blood volume as an index of fuel delivery, astrocytic pyruvate as a metabolic intermediate linking glucose to neuronal use, and neuronal ATP as the immediate energy currency within nerve cells.
Key findings
- Pre-REM vascular surge: Brain blood volume begins to rise roughly 50 seconds before the conventional onset of REM sleep, first appearing in the posterior cortex and then propagating forward in a large-scale wave.
- Astrocytic pyruvate increases: After REM begins, astrocytic pyruvate levels rise, signaling enhanced glucose use or greater glycolytic throughput in astrocytes.
- Neuronal ATP decreases: Despite increased blood flow and elevated astrocytic pyruvate, intracellular neuronal ATP drops markedly during REM, indicating that neuronal energy consumption outpaces supply.
- Delta–theta predictive coupling: During non-REM sleep, subtle theta-band fluctuations in neuronal activity predict local blood volume changes several seconds later, demonstrating tight neurovascular coupling even in sleep.
- Likely causes of ATP decline: The ATP drop is likely driven by energy-intensive processes during REM, such as hippocampal–cortical communication, synaptic reorganization, and memory consolidation that occur during vivid dreaming.
Source: Tohoku University
The brain consumes more energy than most organs and must allocate limited resources flexibly across different behavioral and internal states. Sleep, though outwardly restful, is a period of intense and state-specific brain activity. REM sleep in particular combines wake-like electrical activity with muscle atonia, which is why it has long been called “paradoxical sleep.” The new study reveals a second paradox: while vascular and astrocytic indicators suggest greater fuel availability during REM, neuronal ATP declines.
The research team, led by investigators at Tohoku University, maintained a transparent skull window in mice using a UV-curable resin and applied wide-field fluorescence imaging to observe natural sleep without disrupting it. This approach allowed continuous, simultaneous measurement of intrinsic optical signals for cerebral blood volume, fluorescent biosensors for astrocytic pyruvate, and neuronal ATP levels across sleep cycles.
During non-REM sleep, strong delta-band activity dominates, but the investigators emphasize that theta-band fluctuations—although subtler—also play a meaningful role. These theta fluctuations predicted blood volume changes several seconds later, suggesting the sleeping brain dynamically adjusts vascular supply in response to ongoing neuronal activity and metabolic need.
By contrast, the transition into REM sleep displayed a distinct sequence: roughly fifty seconds before REM onset, blood volume began to rise in the posterior cortex and propagated anteriorly, consistent with a coordinated, brain-wide metabolic preparation. Once REM began, astrocytic pyruvate rose, indicating increased substrate availability or astrocytic glycolysis. Paradoxically, neurons showed a sharp decline in ATP.
Several nonexclusive mechanisms could account for the ATP decrease. Neuronal processes tied to memory consolidation—such as replay of hippocampal patterns, large-scale circuit reconfiguration, and synaptic remodeling—are energy demanding and may consume ATP faster than it can be replenished. Alternatively, state-dependent shifts in how astrocytes shuttle metabolic substrates to neurons or changes in mitochondrial ATP production could contribute.
Beyond the specific observations, the findings point to a broader principle: biological intelligence operates under tight metabolic constraints and allocates energy flexibly rather than uniformly. REM sleep appears to be a natural example of how the brain reorganizes its energy economy to support complex internal computation, trading off increased vascular fueling and astrocytic substrate provision against very high neuronal consumption.
Understanding this balance between supply and demand has practical implications. Sleep supports memory consolidation and cognitive function, and insights into the metabolic economy of sleep may shed light on why dreaming can feel mentally exhausting and how sleep quality influences mental performance.
Frequently asked questions
A: REM is termed paradoxical because the body shows muscle atonia while the brain displays high-frequency, wake-like electrical activity. This study uncovers an additional paradox: despite increased blood flow and apparent fuel delivery, neuronal ATP falls during REM.
A: The decline likely reflects very high neuronal energy expenditure during REM to support processes such as hippocampal–cortical communication, synaptic reorganization, and memory consolidation. These demands can outstrip the rate at which ATP is regenerated.
A: The researchers used a transparent skull window in mice and real-time wide-field fluorescence imaging to monitor cerebral blood volume, astrocytic pyruvate, and neuronal ATP concurrently as animals cycled naturally through non-REM and REM sleep.
Editorial notes
- This article was edited by a Neuroscience News editor.
- The original journal paper was reviewed in full by the editorial team.
- Additional context and clarification were provided by staff writers.
About this research
Author: Public Relations Office, Tohoku University
Source: Tohoku University
Contact: Public Relations Office – Tohoku University
Image credit: 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
Information processing in the brain depends on precisely regulated energy dynamics, yet how metabolic supply is matched to changing computational demands across behavioral states is not well understood. Using wide-field fluorescence imaging through the intact skull of live mice, researchers simultaneously monitored brain blood volume, astrocytic pyruvate, and neuronal ATP during natural sleep.
They found that large-scale metabolic dynamics are coupled to neuronal activity but reorganize depending on sleep state. During non-REM sleep, theta-band electrocorticogram activity predicted subsequent blood volume changes and was associated with rapid anterior-to-posterior vascular waves. In contrast, REM sleep featured a pronounced increase in cerebral blood volume that began in posterior cortex and propagated across the brain, together with elevated astrocytic pyruvate and a paradoxical decline in neuronal ATP. These results highlight a dynamic interplay among neurons, astrocytes, and the vasculature and suggest distinct energy-allocation strategies that underlie the brain’s computational flexibility.