Addicted to dreaming

How human brains regulate sleep remains an enduring puzzle (1). How sleep subserves human dreaming—rapid eye movement (REM) sleep—is especially puzzling. There is considerable mechanistic understanding of the synaptic, cellular, and circuit bases of REM sleep (2, 3). However, despite pharmacological evidence that dopamine (DA) can potently modulate REM sleep, this neurotransmitter is conspicuously absent from most prevailing REM sleep circuit models.