Spatiotemporal Oscillatory Patterns During Working Memory Maintenance in Mild Cognitive Impairment and Subjective Cognitive Decline

Working memory (WM) is a crucial cognitive process and its disruption is among the earliest symptoms of Alzheimer's disease. While alterations of the neuronal processes underlying WM have been evidenced in mild cognitive impairment (MCI), scarce literature is available in subjective cognitive decline (SCD). We used rnagnetoencephalography during a WM task performed by MCI (n = 45), SCD (n = 49) and healthy elders (n 49) to examine group differences during the maintenance period (0-4000 ms). Data were analyzed using time-frequency analysis and significant oscillatory differences were localized at the source level. Our results indicated significant differences between groups, mainly during the early maintenance (250-1250 ms) in the theta, alpha and beta bands and in the late maintenance (2750-3750 ms) in the theta band. MCI showed lower local synchronization in fronto-temporal cortical regions in the early theta-alpha window relative to controls (p = 2 x 10(-03)) and SCD (p = 4 x 10(-03)), and in the late theta window relative to controls (p =1 x 10(03)) and SCD (p = 0.01). Early theta-alpha power was significantly correlated with memory scores (rho = 0.24, p = 0.02) and late theta power was correlated with task performance (rho = 0.24, p = 0.03) and functional activity scores (rho = -0.23, p = 0.02). In the early beta window, MCI showed reduced power in ternporo-posterior regions relative to controls (p = 3 x 10(-03)) and SCD (p = 0.02). Our results may suggest that these alterations would reflect that memory-related networks are damaged.