Inferior Parietal Perfusion, Lateralization, and Neuropsychological Dysfunction in Alzheimer's Disease

The severity of inferior parietal perfusion deficits in Alzheimer's disease (AD) is strongly associated with global intellectual decline. The relationship to specific losses of neuropsychological functioning, however, is less clear, as is the relative importance of the side (left vs. right) of hemispheric deficit. In this study, 53 patients with probable AD and 35 elderly controls received both a resting¹³³Xe rCBF measurement and neuropsychological examination. AD patients demonstrated the expected bilateral deficits in inferior parietal perfusion, as well as impairment on measures of mental status, intelligence, verbal and visual memory, attention, language, and construction abilities. The severity of this bilateral parietal deficit, in turn, was associated with virtually all of these AD-related neuropsychological impairments, most strongly with declining Performance IQ. Left-sided deficits correlated better with overall declines in IQ, as well as with declining attention and language fluency. Right-sided deficits, on the other hand, correlated best with declines in mental status and—paradoxically—verbal memory and contributed independently to declines in Full Scale and Performance IQ. In terms of the number and strength of their association to neuropsychological measures, left-sided deficits appear much more predictive of cognitive decline in AD. Right-sided deficits, however, may be most important for predicting aspects of performance skill that are only indirectly assessed in standard paper-and-pencil format. Overall, it appears that both sides make significant, but independent contributions to general functional decline in AD, but that left-sided deficits are more closely associated with cognitive decline as measured by most standard neuropsychological measures.