Crystallized and fluid intelligence in elderly patients with mild dementia of the Alzheimer type

To examine early intellectual deficits in elderly patients with dementia of the Alzheimer type (DAT), 25 mildly impaired patients with DAT and 25 normal controls were compared using the Japanese version of the Wechsler Adult Intelligence Scale-Revised (WAIS-R). The two groups did not differ significantly in age, years of education, or sex ratio. Based on Horn's modified fluid and crystallized model, the WAIS-R subtests were classified into two categories (i.e., fluid intelligence and crystallized intelligence). The DAT group showed a significantly lower crystallized intelligence score, whereas the fluid intelligence scores did not differ significantly between the two groups. When the subtests were examined individually, the subtests for crystallized intelligence (i.e., information, comprehension, and similarities) were found to show the most significant deficits. These results suggest that elderly subjects with mild DAT have more impaired crystallized intelligence than those without dementia.