Aging and the encoding of changes in events: The role of neural activity pattern reinstatement

When encountering unexpected event changes, memories of relevant past experiences must
be updated to form new representations. Current models of memory updating propose that
people must first generate memory-based predictions to detect and register that features of the
environment have changed, then encode the new event features and integrate them with
relevant memories of past experiences to form configural memory representations. Each of
these steps may be impaired in older adults. Using functional MRI, we investigated these
mechanisms in healthy young and older adults. In the scanner, participants first watched a
movie depicting everyday activities in a day of an actor’s life. They next watched a second
nearly identical movie in which some scenes ended differently. Crucially, before watching
the last part of each activity, the second movie stopped, and participants were asked to
mentally replay how the activity previously ended. Three days later, participants were asked
to recall the activities. Neural activity pattern reinstatement in medial temporal lobe (MTL)
during the replay phase of the second movie was associated with detecting changes and with
better memory for the original activity features. Reinstatements in posterior medial cortex
(PMC) additionally predicted better memory for changed features. Compared to young
adults, older adults showed a reduced ability to detect and remember changes, and weaker
associations between reinstatement and memory performance. These findings suggest that
PMC and MTL contribute to change processing by reinstating previous event features, and
that older adults are less able to use reinstatement to update memory for changed features.