DOES VISUOSPATIAL MEMORY IN SENILE DEMENTIA OF THE ALZHEIMER TYPE DEPEND ON THE SEVERITY OF THE DISORDER

Visuospatial memory was studied in patients suffering from senile dementia of the Alzheimer type (SDAT). They had been allocated into one of two groups depending on the severity of their disorder (mild or moderate), and a control group of healthy elderly subjects was included. Three different microcomputer-controlled tasks were used. The spatial span task was able to distinguish between the two SDAT groups. Both groups were impaired, relative to control, on spatial recognition. The deficit in spatial working memory was also equivalent in the mild and moderate groups and was accompanied by evidence of an intact strategic approach to the task. The normal positive relationship between spatial memory performance and strategy was in fact reversed in the SDAT groups, suggesting a pure spatial memory deficit. These results show that spatial memory processes are impaired in the early stages of SDAT and get worse as the disease progresses. They also suggest that the neuroanatomical foci of the deficits may be predominantly in posterior cortical regions (including hippocampus), rather than the frontal cortex.