While we dream, the brain is far from resting. A new study published in Communications Biology in 2026 has revealed a fascinating energy paradox during REM sleep – the stage of sleep most strongly associated with vivid dreaming.
What Happens to the Brain During REM Sleep?
Researchers studied brain activity and metabolism in living mice, simultaneously measuring cerebral blood volume, pyruvate levels in astrocytes, and ATP – the primary source of cellular energy – in neurons.
The results were surprising:
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blood supply to the brain increased;
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astrocytic pyruvate levels also increased;
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yet ATP levels inside neurons dropped sharply during REM sleep.
In other words, the brain appears to receive more metabolic resources while the energy immediately available to neurons still declines.
Why Does the Brain Lose Energy While We Sleep?
One possibility is that neurons consume ATP extremely rapidly during REM sleep. REM is associated with intense brain activity, coordinated neural processes, communication between the hippocampus and cortex, and synaptic changes involved in memory.
Scientists, however, do not yet know the exact cause. Besides increased ATP consumption, possible explanations include changes in how astrocytes supply energy substrates to neurons or a temporary reduction in ATP production by mitochondria.
Does Dreaming Really Drain the Brain?
We cannot yet say that dreaming itself causes this drop in energy. The study was conducted in mice and identified the phenomenon during REM sleep rather than demonstrating a direct cause-and-effect relationship between dreams and ATP consumption.
Still, the discovery reveals something remarkable: while the body appears peaceful, the brain can enter an extremely dynamic metabolic state. Sleep is not simply the brain “switching off” – at times, it may involve remarkably intense internal activity.
Source: Yusuke Takahashi, Yoko Ikoma & Ko Matsui, “Energy paradox in REM sleep: balancing supply and consumption in brain metabolism”, Communications Biology, Volume 9, Article 979 (2026), published July 27, 2026.
