Clinicians screening for Alzheimer's disease in highly intelligent, older people may better predict cognitive decline by scoring an individual's test performance against a higher "average" score for their intelligence, rather than against the average score of the general population, says a recent study in the APA journal Neuropsychology (Vol. 18, No. 1).
In the study, psychologist Dorene Rentz, PsyD, of Brigham and Women's Hospital and Harvard Medical School, and her colleagues tested the IQ of 221 participants in an ongoing study of aging and Alzheimer's disease. From that group, Rentz selected 42 participants, ages 63 to 88, with an estimated IQ of 120 or higher. The researchers gave the participants a battery of cognitive tests measuring their memory, language, visuospatial processing and executive skills and then compared these baseline results with results of retests administered more than 3.5 years later.
Rentz examined the test performances using standardized, published norms for age, as well as a higher, adjusted test score expected of someone with an IQ of 120 or higher. She found that the new norms, adjusted higher for IQ, predicted declines in participants' memory--suggestive of early Alzheimer's disease--3.5 years before the standard norms did.
For example, 11 of the 42 participants showed significant memory impairment at baseline--scoring more than 1.5 standard deviations below their higher, adjusted mean--even though the standard, published averages indicated those participants tested normally. At retest, six of those 11 participants tested more than 1.5 standard deviations below even the published averages for the general population--low enough to meet criteria for mild cognitive impairment, a preclinical condition that often precedes an Alzheimer's-type dementia.
The findings indicate that, despite possible early decline, highly intelligent older people use their additional mental reserves to excel on cognitive tests, thereby initially masking the first signs of problems, Rentz says. To unmask them, "Different standards are necessary for assessing early cognitive decline when individuals vary from the normative group," she says, adding, "I'm hoping this work will help clinicians to diagnose and treat early Alzheimer's disease in highly intelligent older individuals."