Functional connectivity in auditory-verbal short-term memory in Alzheimer's disease.

Alzheimer's disease (AD) patients show normal patterns of regional cerebral blood flow during performance of subspan verbal memory tasks, but appear to allocate new brain regions when performing supraspan recall tasks. To understand the relationships among these interconnected brain regions, their functional connectivity was considered using principal components analysis (PCA). AD patients and controls were scanned in four conditions: visual fixation only and visual fixation with one-word recall, three-word recall, and eight-word recall. When applied to the data from the three recall task conditions (i.e., eliminating fixation), PCA revealed a significant first component accounting for 75.8% of the variance in the control data and 66.8% of the variance in the patient data. The one-word recall condition had a high positive component score, and the eight-word condition a high negative score. The correlations of individual voxels on this factor (i.e., spatial modes) were very similar between the patients and the controls. The overall similarity in the results of the PCAs between the patients and the controls suggests that they have similar functional connectivity. This would suggest that, at least in the early course of the dementia, the functional CNS organization of verbal memory systems remains normal.