Locus coerulus

The locus coerulus is a group of cells in either side of the pons, whose activity is related to the circadian rhythm of the sleep-wake cycle and seems to be responsible for initiating REM sleep after a period of slow wave sleep. It has also been linked to fear and anxiety.

Axons run from this are throughout the neocortex, thalamus, hippocampus and the cerebellum and other areas of the pons, secreting norepinephrine and serotonin