Neural reinstatement and sequential reactivation of navigational episodic memory and its age-related decline

When we retrieve memories of past navigational episodes, our brain reactivates cortical representations of the spatial information experienced along the way. Although navigation is temporally dynamic in nature, previous studies on cortical memory reactivation have mostly focused on single items or their associated contexts. In this study, we aimed to investigate whether sequential reactivation of navigational events can be measured from cortical electrophysiological activity and is influenced by factors such as age or the availability of spatial cues. Participants were passively navigated through virtual environments and then asked to remember the routes or destinations that they traveled to. Each navigational episodes contained an average of five turns and varied in the presence or absence of landmarks. Given the decline in navigational abilities in aging, we separately tested younger (ages 22-32) and middle-aged participants (ages 41-63) to identify age-related differences in cortical memory reactivation. Comparing EEG spectral patterns between navigational encoding and retrieval, we found that sequential reactivation of turn events was associated with successful spatial memory in younger adults. This sequential reactivation was correlated with the reinstatement of neural activity during distal landmark-viewing and was primarily driven by theta and alpha oscillations. Although middle-aged adults showed a decrease in sequential reactivation overall, those with preserved landmark reinstatement and sequential reactivation patterns exhibited better spatial memory. These results may have implications not only for our understanding of the electrophysiological correlates of navigation and its age-related changes but also for the broader importance of cortical reactivation in episodic memory retrieval.