P2-173: Impairment of spatial memory in patients with mild cognitive impairment precedes development of Alzheimer’s disease

Abstract

Hippocampus dependent spatial navigation is impaired early among the cognitive functions, but has been little studied in Alzheimer's disease (AD) and in Mild Cognitive Impairment (MCI). Failure in real life space orientation is common in AD patients and may be an early symptom of hippocampal damage in MCI patients. To evaluate contribution of spatial memory testing as a potential biomarker in MCI and in AD. 37 patients were recruited among clients of our Memory Disorders Clinic and subsequently classified into 3 groups: probable AD (n=20), amnestic MCI (n=8), subjective memory complaints not fulfilling MCI criteria (SMC)(n=9). Results were referred to age and sex matched control group (n=15). Diagnosis of AD dementia was based on DSM IV and NINCDS– ADRDA criteria. Petersen's criteria for MCI were applied. MRI, MMSE and extensive neuropsychological testing were done in all subjects. Spatial memory was tested in an enclosed arena 2.9m in diameter with orientation cues on the wall and in a P.C. version with a map view of the arena projected on a monitor. The test called the Hidden Goal Task (HGT) was used—the subjects should locate a hidden goal inside of the arena in 4 subtests. Depending on the subtest, the subjects used the start position and/or cues on the wall for navigation to focus on either allocentric or egocentric navigation. The searching trajectory was recorded by an overhead camera and a P.C. tracking system. A significantly worse performance in AD group compared to controls (p <0.01) was proved; amnestic MCI group was significantly impaired in subtests focused on egocentric (p <0.05) and allocentric (p <0.01) orientation compared to controls, but less than in AD (p <0.05). SMC group wasn't significantly impaired in any of the subtests compared to controls. MMSE test correlated with HGT results (p <0.01). Spatial memory deficit in MCI patients is less profound than among AD patients, but it is qualitatively similar. Spatial memory testing can be profitable for the assessment of real life disability, longitudinal monitoring and prognosis of AD development in patients with amnestic MCI.