Our previous lesion and tracing studies identify the parabrachial nucleus (PB) as the key structure in the brainstem for cortical arousal and wakefulness and we hypothesize that the PB is the key structure of ascending reticular activating system (ARAS). We further show that PB, via the basal forebrain (BF) not the thalamus, regulates cortical arousal (consciousness). In this grant proposal, we will apply a novel approach chemogenetics (or DREADD) to selectively activate the neurons in the PB, their projections to the preoptic, posterior lateral hypothalamus (pLH), basal forebrain (BF) and thalamus and examine and identify the role of each projection in mediating the PB control in cortical arousal and wakefulness. In Specific Aim 1, we will test the effect of PB activation on wakefulness. In Specific Aim 2, we will examine the effects of long wakefulness and high sleep pressure produced by repeat activation of the PB on sleep-wake circuits and sleep rebound. In Specific Aim 3, we will selectively stimulate the pathways of PB-BF, PB-preoptic, PB-pLH and PB-thalamus and dissect which pathway is involved in regulation cortical arousal or general wakefulness. In Specific Aim 4, we will investigate the interaction between the PB and medullary sleep center, parafacial zone (PZ). We hypothesize that the PB inhibits PZ. This inhibition is via the GABAergic neurons in the retrorubral field (RRF). This inhibition, together with previous finding that PZ inhibits the PB, forms co-inhibitory circuit that regulates sleep-wake behavior.