Neural correlates of subsequent recollection and familiarity in ageing

It is now commonly accepted that, in ageing, recollection processes are impaired and familiarity seems to be relatively preserved. In this study, we were interested in the differences between younger and older participants regarding cerebral activity during encoding depending on whether the item later elicited recollection or familiarity. Twenty young volunteers and 19 older volunteers were presented visual stimuli depicting objects. After a first fMRI session in which the items were encoded, they underwent a recognition memory task in which they judged whether items were Remembered, Familiar or New. Data were analysed using SPM8, with an event-related design comparing modifications in cerebral activity between the two subjects groups during encoding (1) for the items leading to recollection compared to those leading to familiarity, and (2) for the items associated with familiarity compared to those which were not recognized. Results showed that older adults displayed a heightened activity in regions of the default-mode network for subsequent recollection. As it does not appear to be deleterious, it could stem from a more frequent use of self-referential appraisal as an encoding strategy in older adults. Furthermore, they show supplementary contralateral activations in frontal and temporal regions, which could be indicative of dedifferentiation or attempted compensation. To conclude, it appears that despite relying less on elaborative encoding, older adults seem to be able to perform recollection using qualitatively different strategies than young adults.