Epidemiological and experimental findings suggest that chronic infection with Herpes simplex virus type 1 (HSV-1) may be a risk factor for Alzheimer's disease (AD), but the molecular mechanisms underlying this association have not been fully identified. We investigated the effects of HSV-1 on excitability and intracellular calcium signaling in rat cortical neurons and the impact of these effects on amyloid precursor protein (APP) processing and the production of amyloid-β peptide (Aβ). Membrane depolarization triggering firing rate increases was observed shortly after neurons were challenged with HSV-1 and was still evident 12 hours postinfection. These effects depended on persistent sodium current activation and potassium current inhibition. The virally induced hyperexcitability triggered intracellular Ca(2+) signals that significantly increased intraneuronal Ca(2+) levels. It also enhanced activity- and Ca(2+)-dependent APP phosphorylation and intracellular accumulation of Aβ42. These findings indicate that HSV-1 causes functional changes in cortical neurons that promote APP processing and Aβ production, and they are compatible with the co-factorial role for HSV-1 in the pathogenesis of AD suggested by previous findings.