Verbal fluency activates the left medial temporal lobe: A functional magnetic resonance imaging study

Verbal fluency tests (VFTs) are suggested to assess frontal lobe function. This view is supported by functional imaging studies that report left front al activation during VFTs. VFTs require retrieval of semantically associate d words from long-term memory storage. The neural networks that participate in this process, however, are largely unknown. These neural networks are o f interest, given that patients with early Alzheimer's disease, typically w ithout frontal pathology, are often impaired in VFTs. In the present study, functional magnetic resonance imaging was performed to determine brain act ivation areas during VFTs in young subjects, in the activation task, catego ry fluency was contrasted with orderly listing of numbers. As judged from u sing this comparison, there was activation in the left medial temporal lobe , in the inferior frontal and retrosplenial cortices bilaterally, and in th e left superior parietal lobule. Left medial temporal lobe activation was p resent in 13 of the 14 study subjects either in the hippocampal formation ( 11 of 14) or in the posterior parahippocampal gyrus (12 of 14). These resul ts suggest that the medial temporal lobe is required for the process of ret rieval by category. Functional magnetic resonance imaging combined with a c ategory fluency task may provide a new method to study patients with early Alzheimer's disease.