The neural correlates of naming and fluency deficits in Alzheimer's disease: an FDG-PET study.

Objective: To examine the neural processes associated with language deficits in Alzheimer's disease (AD), and in particular to elucidate the correlates of confrontation naming and word retrieval impairments.

Methods: Sixty patients with probable AD were included. Confrontation naming was assessed using the number of words spontaneously named correctly on the Boston Naming Test. We recorded the number of additional words stated following phonemic cuing. We also assessed phonemic (FAS) and semantic (supermarket items) fluency. We then correlated performance on each measure with resting cortical metabolic activity using FDG-PET images.

Results: We found that poorer ability to spontaneously name an object was associated with hypometabolism of bilateral inferior temporal lobes. In contrast, when a phonemic cue was provided, successful naming under this condition was associated with higher metabolic activity in bilateral inferior frontal gyrus (IFG), right superior frontal gyrus (SFG), left temporal, and occipital regions. Consistent with these findings, we found that poorer semantic fluency was associated with hypometabolism in regions including both IFG and temporal regions, and poorer phonemic fluency was associated with hypometabolism in only left IFG. Across analyses, measures that required cued retrieval were associated with metabolism in the left IFG, whereas measures taxing semantic knowledge were associated with metabolic rate of left temporal cortex.

Conclusions: Naming deficits in AD reflect compromise to temporal regions involved in the semantic knowledge network, and frontal regions involved in the controlled retrieval of information from that network.