The long-term objective of this project is to further elucidate the neurocognitive underpinnings of the distinction in language between idiosyncratic and rule-governed mappings. The project examines four issues - separability, computation/representation, domain-specificity/-generality, and neural correlates - in the context of competing neurocognitive models of language. Dual-system models claim that idiosyncratic mappings are stored in the mental lexicon, while the mental grammar underlies the rule-governed composition of complex linguistic representations. One such view - the declarative/procedural model - argues that the lexicon depends on the temporal-lobe- declarative memory system, whereas grammar involves the frontal/basal-ganglia procedural memory system. Single-system models posit one computational system, denying a categorical distinction between the two types of mapping. Previous psycholinguistic, developmental, neurological and neuroimaging studies, largely on regular/irregular morphology, have begun to tease apart the models. We propose to replicate and extend the research in two dimensions. (1) Linguistic domains: We will examine morpho-phonology (in regular/irregular past tense, past participle, plural, and derivational morphology), syntax (in the complement/adjunct distinction, and in the hierarchy of morphosyntactic functional categories), and compositional semantics (in the definiteness effect, and negative polarity items). (2) Subject groups: Preliminary data suggest that men and women differ in their relative reliance on the two brain systems: Whereas men tend to compose complex linguistic representations, women tend to memorize them. Thus we introduce sex as an important design factor. Specific aims: We will test the predictions of the competing models with two complementary studies: (i) a neuroimaging study of cognitively unimpaired adults, using ERPs, fMRI and dipole modeling;and (ii) a psycholinguistic and neurological study of healthy adults and of adult-onset brain-damaged patients.