Effects of age on the neural correlates of familiarity as indexed by ERPs.

ERPs were recorded from samples of young (18-29 years) and older (63-77 years) participants while they performed a modified "remember-know" recognition memory test. ERP correlates of familiarity-driven recognition were obtained by contrasting the waveforms elicited by unrecollected test items accorded "confident old" and "confident new" judgments. Correlates of recollection were identified by contrasting the ERPs elicited by items accorded "remember" and confident old judgments. Behavioral analyses revealed lower estimates of both recollection and familiarity in older participants than in young participants. The putative ERP correlate of recollection-the "left parietal old-new effect"-was evident in both age groups, although it was slightly but significantly smaller in the older sample. By contrast, the putative ERP correlate of familiarity-the "midfrontal old-new effect"-could be identified in young participants only. This age-related difference in the sensitivity of ERPs to familiarity was also evident in subgroups of young and older participants, in whom familiarity-based recognition performance was equivalent. Thus, the inability to detect a reliable midfrontal old-new effect in older participants was not a consequence of an age-related decline in the strength of familiarity. These findings raise the possibility that familiarity-based recognition memory depends upon qualitatively different memory signals in older and young adults.