Neuroanatomical correlates of verbal fluency in early Alzheimer's disease and normal aging.

Verbal fluency (VF) impairments occur early in Alzheimer's disease (AD) and to a lesser extent also in normal aging. However, the neural underpinnings of these impairments are not fully understood. The present study evaluated whether VF impairments in early AD and normal aging rely upon common or different neuroanatomical correlates. We examined the association between VF performance and brain structure in 18 mild AD patients and 24 healthy elderly. Linear regressions were performed between accuracy and time intervals in VF scores and structural measurements of cerebral gray matter (GM) and white matter (WM) using MRI. Results showed that semantic VF correlated exclusively with GM in cerebellum, left temporal fusiform cortex, and WM in uncinate fasciculus, inferior fronto-occipital fasciculus and corpus callosum. Phonemic VF showed unique associations between intervals and WM in left-hemisphere tracts. The association between GM in hippocampus, subcortical structures and semantic accuracy differentiated patients from controls. Results showed that VF impairments are primarily associated with same structural brain changes in AD as in healthy elderly but at exaggerated levels. However, specific VF deficiencies and their underlying neural correlates exist and these clearly differentiate the initial stages of AD.