REM sleep paradox: Dreaming may drain the brain’s energy even as fuel supply rises

Scientists discovered a surprising energy paradox in the brain during REM sleep, the stage most closely associated with dreaming. Blood supply to the brain begins increasing even before REM starts, but neurons’ immediately available energy, measured as ATP, then drops. The finding suggests that dreaming may require such intense internal processing that neurons consume energy faster than it can be replenished.

REM sleep paradox: Dreaming may drain the brain’s energy even as fuel supply rises. Even so, it can continue processing information when energy is limited by adjusting how available resources are used. Scientists are still trying to understand how the brain manages this energy budget as it moves through different internal states.

Sleep offers a useful way to study that question. Although the body is resting, the brain remains active, especially during rapid eye movement (REM) sleep, which is closely associated with dreaming and memory processing. REM sleep is often described as "paradoxical sleep" because the body is mostly still while brain activity resembles wakefulness.