Impaired episodic memory network in subjects at high risk for Alzheimer's disease.

Episodic memory dysfunction is one of the hallmark symptoms of Alzheimer's disease (AD) and mild cognitive impairment (MCI). This cognitive impairment may be related to abnormal brain structure and activity. Functional connectivity mapping (FCM) analysis provides a powerful tool for exploring the topology of human brain function using magnetic resonance imaging (MRI). Thus, it would be advantageous to investigate the changes in functional connectivity within the episodic memory network in a longitudinal MCI dataset, as it may be helpful in identifying a potential marker of disease progress. Accordingly, FCM was performed in 23 normal control (NC) subjects, 26 patients with early MCI (EMCI) and 19 patients with late MCI (LMCI). Our results demonstrated that patients with MCI showed affected functional connectivity within the right fusiform gyrus (rFG) and between the rFG and right precuneus (rPreCU) compared to NCs. The results indicated that deficits in episodic memory would lead to impaired functional connectivity associated with visual information processing in early MCI. FCM may be helpful for exploring a sensitive marker of disease presence.