4 aminobutyric acid 1 Alzheimer disease 1 Alzheimer's disease 1 Human aging 1 Locus coeruleus 1 Norepinephrine 1 REM sleep 1 Review 1 Sleep microstructure 1 Sleep-wake regulation 1 Tau pathology 1 acetylcholine 1 adrenergic system 1 aging 1 anterior hypothalamus 1 basal forebrain 1 brain function 1 circadian rhythm 1 clonidine 1 dexmedetomidine 1 dopamine 1 drug mechanism 1 electrophysiology 1 glutamic acid 1 human 1 hypothalamus 1 lateral hypothalamus 1 laterodorsal tegmental nucleus locus ceruleus 1 melanin concentrating hormone 1