MAPT and early-onset autosomal dominant Alzheimer disease: <h4>Purpose of review</h4>To summarize recent animal, postmortem and in vivo human studies examining the role of the noradrenergic and serotonergic system in the pathophysiology and symptomatology of Alzheimer's disease (AD).<h4>Recent findings</h4>Early in adulthood, the locus coeruleus and raphe nucleus accumulate tau, undergo morphological changes, and exhibit hyperexcitability, which contributes to the development of neuropsychiatric symptoms.