REM sleep readiness and duration are encoded during NREM by spinal-projecting sublaterodorsal (SLD) neurons.

We identify a subpopulation of spinal-projecting neurons in the sublaterodorsal nucleus (SLDsp neurons) that act as a dynamic “readiness signal” for REM sleep in mice. SLDsp activity during non-REM (NREM) sleep reliably predicts both the likelihood of NREM-to-REM transition and the duration of the subsequent REM bout.

This activity dynamically reflects REM sleep pressure, as increased pressure shortens the pre-transition rise time and lowers the transition threshold. Optogenetic activation of SLDsp neurons promotes REM sleep, while chemogenetic inhibition suppresses REM transitions, even under heightened REM pressure. Furthermore, SLDsp ablation disrupts REM sleep homeostasis, induces hyperarousal, hinders recovery from sleep deprivation, and impairs memory consolidation.