Understanding Sleep
Stages of Sleep
Sleep-Wake Cycles
Substance Use Disorders Affecting Sleep
Insufficient Sleep and Sleep Deprivation
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Updated: Aug 20, 2025

Automated Measurements of Sleep and Locomotor Activity in Mexican Cavefish
Published on: March 21, 2019
Niels C Rattenborg1, Gianina Ungurean1
1Max Planck Institute for Biological Intelligence (in foundation), Seewiesen, Germany.
The evolutionary origins of sleep and its sub-states, rapid eye movement (REM) and non-REM (NREM) sleep, remain a mystery. Recent discoveries in diverse animals suggest sleep evolved earlier and diversified into multiple types, offering insights into its functions.
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