Cholinergic projections from the basal forebrain and brainstem are thought to play important roles in rapid eye movement(REM)sleep and arousal.Using transgenic mice in which channelrhdopsin-2is selectively expressed in cholinergic neurons,we show that optical stimulationof cholinergic inputs to the thalamic reticular nucleus(TRN)activates local GABAergic neurons topromote sleep and protect non-rapid eye movement(NREM)sleep.It does not affect REM sleep.Instead,direct activation of cholinergic input to the TRN shortens the time to sleep onset andgenerates spindle oscillations that correlate with NREM sleep.It does so by evoking excitatorypostsynaptic currents via a7-containing nicotinic acetylcholine receptors and inducing bursts ofaction potentials in local GABAergic neurons.These findings stand in sharp contrast to previousreports of cholinergic activity driving arousal.Our results provide new insight into the mechanismscontrolling sleep.