Effects of Apolipoprotein E Genotype on the Off-Line Memory Consolidation

Spontaneous brain activity or off-line activity after memory encoding is associated with memory consolidation. A few recent resting-state functional magnetic resonance imaging (RS-fMRI) studies indicate that the RS-fMRI could map off-line memory consolidation effects. However, the gene effects on memory consolidation process remain largely unknown. Here we collected two RS-fMRI sessions, one before and another after an episodic memory encoding task, from two groups of healthy young adults, one with apolipoprotein E (APOE) epsilon 2/epsilon 3 and the other with APOE epsilon 3/epsilon 4. The ratio of regional homogeneity (ReHo), a measure of local synchronization of spontaneous RS-fMRI signal, of the two sessions was used as an index of memory-consolidation. APOE epsilon 3/epsilon 4 group showed greater ReHo ratio within the medial temporal lobe (MTL). The ReHo ratio in MTL was significantly correlated with the recognition memory performance in the APOE epsilon 3/epsilon 4 group but not in epsilon 2/epsilon 3 group. Additionally, APOE epsilon 3/epsilon 4 group showed lower ReHo ratio in the occipital and parietal picture-encoding areas. Our results indicate that APOE epsilon 3/epsilon 4 group may have a different off-line memory consolidation process compared to epsilon 2/epsilon 3 group. These results may help generate future hypotheses that the off-line memory consolidation might be impaired in Alzheimer's disease.