Abstract
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) ε2/ε3 and the other with APOE ε3/ε4. 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 ε3/ε4 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 ε3/ε4 group but not in ε2/ε3 group. Additionally, APOE ε3/ε4 group showed lower ReHo ratio in the occipital and parietal picture-encoding areas. Our results indicate that APOE ε3/ε4 group may have a different off-line memory consolidation process compared to ε2/ε3 group. These results may help generate future hypotheses that the off-line memory consolidation might be impaired in Alzheimer’s disease.
Highlights
Muller and Pilzecker assumed that new memory takes time to be consolidated after encoding [1]
One study used perfusion MRI and found that the regional cerebral blood flow increased in hippocampal and temporal lobe regions after a learning task and that the increases correlated with the performance of surprised recall task [10]. Another very recent study from our group found that the local synchronization of spontaneous fMRI signal in the medial temporal lobe (MTL) increased after an episodic memory task in a group of participants having better performance in a later surprise retrieval task, but not in a group having worse performance [11]
resting-state functional magnetic resonance imaging (RS-fMRI) Results in MTL In MTL Region of Interest (ROI), two sample t-test showed that the regional homogeneity (ReHo) ratio in apolipoprotein E (APOE) e3/e4 group was significantly larger than that in APOE e2/e3 group (p,0.05, two-tailed, small volume correction (SVC))
Summary
Muller and Pilzecker assumed that new memory takes time to be consolidated after encoding [1]. Recent RS-fMRI studies have indicated an association of spontaneous brain activity with memory consolidation of recent scenarios [3,4,5,6] These results support the system consolidation theory, which hypothesized that the MTL (mainly hippocampus and parahippocampus) is required for initial storage and recall and that the neo-cortex is considered as the area where remote memory is stored [7,8]. One study used perfusion MRI and found that the regional cerebral blood flow increased in hippocampal and temporal lobe regions after a learning task and that the increases correlated with the performance of surprised recall task [10] Another very recent study from our group found that the local synchronization of spontaneous fMRI signal in the MTL increased after an episodic memory task in a group of participants having better performance in a later surprise retrieval task, but not in a group having worse performance [11]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
