Oct. 13, 2000

Gene May be Linked to Deficits in Attention Tasks, Research Shows

The presence of a gene linked to Alzheimer's disease has also been linked to deficits in the cognitive ability of visual attention in middle-aged individuals who don't yet show symptoms of having the disease, according to researchers at The Catholic University of America and the National Institute of Mental Health's Geriatric Psychiatry Branch.

The e4 allele of the apolipoprotein E (APOE) gene, often present in individuals with Alzheimer's disease, has been associated with altered brain physiology in healthy adults prior to old age. The researchers found middle-aged, non-demented carriers of the gene showed deficits in two out of three tasks that measured their visual attention.

Their findings, published in the October 10, 2000, issue of the Proceedings of the National Academy of Sciences, could provide valuable information in the development of a diagnostic test for middle-aged adults at risk of developing the debilitating disease. The study was conducted by Pamela M. Greenwood, associate professor and research fellow with CUA's Cognitive Science Laboratory; Trey Sunderland and Judy L. Friz of the National Institute of Mental Health; and Raja Parasuraman, professor of psychology and director of the Cognitive Science Laboratory.

At the heart of the research is a question: whether evidence of cognitive change can be detected in healthy, middle-aged individuals at increased risk of Alzheimer’s disease years before they would be expected to show clinically significant cognitive decline. A secondary question concerns whether memory declines first in patients with Alzheimer’s disease. Attention, Parasuraman pointed out, is a basic cognitive process thought to be a foundation for memory. The researchers conducted three different studies to assess performance of separate aspects of visual attention: the ability to shift attention, adjust the spatial scale of attention and sustain attention throughout a visual task.

Of the 97 individuals tested, 74 had close relatives diagnosed with Alzheimer's disease. DNA testing determined whether participants were carriers of the e2, e3 or e4 allele of the APOE gene, and they were grouped accordingly.

In the first test, research subjects were placed at a computer and asked to identify whether a letter flashing on an empty screen was a vowel or consonant. Arrows on the screen also appeared as location cues, but were invalid part of the time, requiring participants to shift their attention to find the letter elsewhere. Overall, the e4 group was slower to shift attention away from invalid cues, similar to results seen in individuals with mild early Alzheimer's.

In a second task that more closely resembles visual attention in everyday life, the subjects were asked to pick out a target (a red T) from an array of letters. A rectangular cue varied in size according to the number of letters enclosed in the target and participants were asked to indicate the presence or absence of the target. While all groups performed the task accurately and the search time did not differ significantly among the groups, individuals with the e4 allele were slower to react when they had to narrow in on a smaller target compared to those without the e4 allele.

In the third component of the research project, a vigilance task, the subjects were asked to pick out the target letter O from distracters against a patterned background. No significant differences for the e4 group were found in this task, indicating that the attentional deficits found in the e4 group were not due to non-specific changes in general alertness.

When compared to subjects with mild to moderate Alzheimer's disease, the e4 carriers displayed a pattern of deficits in visual attention closer to that seen in diagnosed Alzheimer's disease patients than to that associated with normal aging. The researchers' next plan is to assemble longitudinal data on the test subjects to see whether the attentional deficits worsen over time, Parasuraman said.

NOTE TO MEDIA: Pamela M. Greenwood and Raja Parasuraman may be contacted directly for interviews. For Greenwood, call 202-319-5816 or e-mail greenwood@cua.edu. For Parasuraman, call 202-319-5755 or e-mail at parasuraman@cua.edu.

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