Why Dreaming Leaves the Brain Running Low on Energy

Researchers at Tohoku University tracked blood volume, astrocyte pyruvate, and neuronal ATP in mice during sleep using wide-field imaging.

When REM sleep began, cortical blood flow and astrocytic metabolic fuel increased, but neuronal ATP still dropped.

This suggests a temporary energy imbalance: more blood flow does not automatically mean more usable energy for neurons.

The findings offer a new framework for understanding why vivid dreaming may be metabolically demanding and how REM sleep supports memory and emotional processing.