Comparative Perspectives that Challenge Brain Warming as the Primary Function of REM Sleep

Highlights

• In many mammals, the brain cools during non-REM sleep and warms during REM sleep
• Pigeons exhibit similar changes in cortical temperature during non-REM and REM sleep
• Brain temperature does not increase during REM-like sleep in bearded dragon lizards
• Brain warming is not a universal outcome of sleep states with wake-like brain activity

Summary

Rapid eye movement (REM) sleep is a paradoxical state of wake-like brain activity occurring after non-REM (NREM) sleep in mammals and birds. In mammals, brain cooling during NREM sleep is followed by warming during REM sleep, potentially preparing the brain to perform adaptively upon awakening. If brain warming is the primary function of REM sleep, then it should occur in other animals with similar states. We measured cortical temperature in pigeons and bearded dragons, lizards that exhibit NREM-like sleep and REM-like sleep with brain activity resembling wakefulness. In pigeons, cortical temperature decreased during NREM sleep and increased during REM sleep. However, brain temperature did not increase when dragons switched from NREM-like to REM-like sleep. Our findings indicate that brain warming is not a universal outcome of sleep states characterized by wake-like activity, challenging the hypothesis that their primary function is to warm the brain in preparation for wakefulness.

Link to the publication :

https://www.sciencedirect.com/science/article/pii/S2589004220308889