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

Abstract

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.

Figure 1

Grand average ERP waveforms elicited by items accorded confident old, confident new and R responses in young subjects. See insert for electrode locations.

Figure 2

Grand average ERP waveforms elicited by items accorded confident old, confident new and R responses in older subjects. See insert for electrode locations.

Figure 3

Grand average ERP waveforms, from left and right frontal electrodes, elicited by items accorded confident old and confident new responses in young and older sub-groups in whom familiarity strength was matched. Box indicates 300–500 ms time interval.

Figure 4

A) Grand average ERP waveforms from the F3 electrode according to the associated recognition judgment in young subjects. B) Mean across-subject ERP amplitudes over 300–500 ms at three left frontal electrode sites. These ERPs were elicited by test items belonging to the four different categories of confidence judgment (from left to right: confident new, unconfident new, unconfident old, confident old, respectively).

Figure 5

Grand average waveforms, from left and right parietal electrodes, elicited by items given confident old, confident new and recollected responses for sub-groups of young and older subjects matched for recollection. Box indicates 500–800 ms time interval.

Figure 6

A) Scalp topography for young subjects of the difference waveforms from 300–500 ms poststimulus onset for items given high confidence old vs. high confidence new judgments. B) Scalp topographies for young and older subjects of the difference waveforms from 500–800 ms poststimulus onset for items given R and high confidence old judgments. Topographic maps are scaled to the maxima (red) and minima (blue) of each effect with the range displayed below each map in microvolts.