During rapid eye movement (REM) sleep emotional memories are consolidated in the prefrontal cortex. Although this front part of the cerebral cortex plays a key role in discriminating between positive versus negatives emotions during wakefulness, it appears paradoxically quiescent during REM sleep. The processes involved, namely the underlying neocortical circuits, remain unclear. 

Mattia Aime, a researcher in the team led by Prof. Adamantidis, aimed at understanding the role of the prefrontal cortex during REM and the underlying cellular mechanisms responsible for emotional processing during this phase of sleep. The researchers first conditioned mice to recognize auditory stimuli associated with safety or danger. They consequently recorded the neuronal response to these stimuli in the mice's brains during sleep-wake cycles and mapped the activity to different parts of the neurons. 

They found that, during REM sleep, the dendrites (finest neuronal ramifications) of prefrontal neurons are highly activated while the cell bodies are kept silent. The scientists found that this decoupling plays an important role in emotional control. On the one hand, the strong activity of the dendrites allows discrimination of positive and negative emotions. On the other hand, the cell bodies remain silent and do not transmit signals during REM sleep, which could help avoiding over-reaction to emotions. In other words, the brain favors the distinction between safety and danger in the dendrites during REM sleep. 

This study identified the neuronal mechanisms by which the brain distinguishes positive from negative emotions during sleep. The results provide a better understanding of how emotions are processed during sleep and open new perspectives for therapeutic targets of affective disorders, including Post-Traumatic Stress Disorder (PTSD).

Paradoxical somatodendritic decoupling supports cortical plasticity during REM sleep. Mattia Aime, Niccolò Calcini, Micaela Borsa, Tiago Campelo, Thomas Rusterholz, Andrea Sattin, Tommaso Fellin, Antoine Adamantidis. Science. 2022 May 13;376(6594):724-730.