![]() Clues to another possible reason for the inconsistent findings may be derived from neuroimaging studies of elderly subjects at risk for AD. Several factors likely contribute to these discrepant findings, including across-study differences in sample size, power, and mean age of the subject groups. The question arises as to why there have been inconsistent findings of attentional deficits in normal elderly at risk for AD. However, several other studies have failed to replicate findings of attentional deficits in nondemented e4 elderly groups ( Baeckman, Small, & Fratiglioni, 2001 Elias et al., 2000 Flory, Manuck, Ferrell, Ryan, & Muldoon, 2000 Smith et al., 1998). Specifically, some studies have found that nondemented elderly with the e4 genotype show subtle deficits on neuropsychological tests that have strong attentional demands, such as the Digit Span subtest ( Albert, Moss, Tanzi, & Jones, 2001 Caselli et al., 1999 Caselli et al., 2001 Linn et al., 1995 Wilson et al., 2002) WMS-R Mental Control subtest ( Tierney et al., 1996), Operation Span Test ( Rosen, Bergeson, Putnam, Harwell, & Sunderland, 2002), Digit Symbol subtest ( Masur, Sliwinski, Lipton, Blau, et al., 1994 Yaffe, Cauley, Sands, & Browner, 1997), attentional switching and disengagement ( Greenwood, Sunderland, Friz, & Parasuraman, 2000 Parasuraman, Greenwood, & Sunderland, 2002), and supra-span ability and divided attention ( Rosen et al., 2002). One area of cognition that has shown promise as a preclinical marker of AD in elderly individuals with the ApoE-e4 allele is attention and working memory. Such research may, in the future, serve as a significant clinical asset if advances in the development of pharmacological agents with neuroprotective properties continue to be made ( Miguel-Hidalgo, Alvarez, Cacabelos, & Quack, 2002 Vajda, 2002). In recent years, neuropsychologists have striven to find the earliest possible cognitive markers of a preclinical phase of Alzheimer's disease (AD) in normal-functioning elderly individuals who are at genetic risk to acquire the disorder because of the apolipoprotein E e4 allele (ApoE-e4) ( Corder, Saunders, Pericak-Vance, & Roses, 1995). The increased discrepancy between verbal and visuospatial attention may reflect the presence of “subgroups” within the ApoE-e4 group that are qualitatively similar to asymmetric subgroups commonly associated with the earliest stages of AD. These findings suggest that contrast measures of modality-specific attentional skills may be more sensitive to subtle group differences in at-risk groups, even when the groups do not differ on individual comparisons of standardized test means. Although the groups’ performances were comparable on the individual attention span tests, the e4+ group showed a significantly larger discrepancy between digit span and spatial span scores compared to the e4- group. We hypothesized that a) the e4+ group would show a higher incidence of asymmetric cognitive profiles when comparing Digit Span/Visual Memory Span performance relative to the e4- group and (b) an analysis of individual test performance would fail to reveal differences between the two subject groups. In this study, we administered the WAIS-R Digit Span and WMS-R Visual Memory Span subtests to 21 nondemented elderly e4+ individuals and 21 elderly e4- individuals matched on age, education, and overall cognitive ability. Comparing genotype groups with individual, modality-specific tests might obscure subtle differences between verbal and visuospatial attention in these asymmetric subgroups. One possible explanation for the inconsistent results could be the presence of subgroups of e4+ individuals with asymmetric cognitive profiles (i.e., significant discrepancies between verbal and visuospatial skills). Some studies of elderly individuals with the ApoE-e4 genotype noted subtle deficits on tests of attention such as the WAIS-R Digit Span subtest, but these findings have not been consistently reported. ![]()
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