Automatic semantic priming of nouns and verbs in patients with Alzheimer's disease

The status of semantic representations of nouns (concrete and abstract) and verbs (motion and non-motion) was investigated in patients with Alzheimer's disease (AD). Nouns and verbs have been argued to activate different neural substrates, given the selective difficulties reported for one or the other grammatical class in patients with focal lesions. Additionally, category-specific deficits have been reported for either abstract or concrete words, often in patients with bilateral neuropathology. We looked for these types of dissociations in patients with AD in a semantic priming experiment using a pronunciation task and a short stimulus onset asynchrony. The normal control subjects demonstrated automatic activation for both concrete nouns and motion verbs. The AD patients, however, demonstrated priming effects for concrete nouns, but not for motion verbs. This dissociation between concrete nouns and motion verbs found for the AD patients is discussed in terms of differences in the nature of semantic representations involving multiple physical and functional attributes in the case of concrete nouns, but only motion attributes in the case of motion verbs. Moreover, the typical distribution of neuropathology associated with AD may put motion verbs at risk, particularly given the neuroanatomical considerations suggested by recent positron emission tomography (PET) studies.