This article investigates how linguistic expressions of time--in particular, temporal adverbs and verb tense morphemes--are used to establish temporal reference at the level of brain physiology. First, a formal semantic analysis of tense and temporal adverbs is outlined. It is argued that computing temporal reference amounts to solving a constraint satisfaction problem. Next, the results of an event-related potential (ERP) study are presented, which suggest that violations of verb tense ("Last Sunday Vincent "paints" the window frames of his country house.") evoke larger left-anterior negativities (LANs) compared to sentences in which verb tense is correct. The semantic analysis is finally combined with a computational, unification-based model of parsing to provide a functional account of the ERP data.