The present study used event-related potentials (ERPs) to investigate how the encoding and recognition of complex scenes change with normal aging. Although functional magnetic resonance imaging (fMRI) studies have identified more drastic age impairments at encoding than at recognition, ERP studies accumulate more evidence for age differences at retrieval. However, stimulus type and paradigm differences across the two literatures have made direct comparisons difficult. Here, we collected young and elderly adults' encoding- and recognition-phase ERPs using the same materials and paradigm as a previous fMRI study [Gutchess, A. H., Welsh, R. C., Hedden, T., Bangert, A., Minear, M., Liu, L., et al. Aging and the neural correlates of successful picture encoding: Frontal activations compensate for decreased medial temporal activity. Journal of Cognitive Neuroscience, 17 , 84–96, 2005]. Twenty young and 20 elderly adults incidentally encoded and then recognized photographs of outdoor scenes. During encoding, young adults showed a frontocentral subsequent memory effect, with high-confidence hits exhibiting greater positivity than misses. Elderly adults showed a similar subsequent memory effect, which, however, did not differ as a function of confidence. During recognition, young adults elicited a widespread old/new effect, and high-confidence hits were distinct from both low-confidence hits and false alarms. Elderly adults elicited a smaller and later old/new effect, which was unaffected by confidence, and hits and false alarms were indistinguishable in the waveforms. Consistent with prior ERP work, these results point to important age-related changes in recognition-phase brain activity, even when behavioral measures of memory and confidence pattern similarly across groups. We speculate that memory processes with different time signatures contribute to the apparent differences across encoding and retrieval stages, and across methods.

We investigated the hypothesis that increased prefrontal activations in older adults are compensatory for decreases in medial-temporal activations that occur with age. Because scene encoding engages both hippocampal and prefrontal sites, we examined incidental encoding of scenes by 14 young and 13 older adults in a subsequent memory paradigm using functional magnetic resonance imaging (fMRI). Behavioral results indicated that there were equivalent numbers of remembered and forgotten items, which did not vary as a function of age. In an fMRI analysis subtracting forgotten items from remembered items, younger and older adults both activated inferior frontal and lateral occipital regions bilaterally; however, older adults showed less activation than young adults in the left and right parahippocampus and more activation than young adults in the middle frontal cortex. Moreover, correlations between inferior frontal and parahippocampal activity were significantly negative for old but not young, suggesting that those older adults who showed the least engagement of the parahippocampus activated inferior frontal areas the most. Because the analyses included only the unique activations associated with remembered items, these data suggest that prefrontal regions could serve a compensatory role for declines in medial-temporal activations with age.

Age differences in frontal and hippocampal activations in working memory were investigated during a maintenance and subsequent probe interval in an event-related fMRI design. Younger and older adults either viewed or maintained photographs of real-world scenes (extended visual or maintenance conditions) over a 4-sec interval before responding to a probe fragment from the studied picture. Behavioral accuracy was largely equivalent across age and conditions on the probe task, but underlying neural activations differed. Younger but not older adults showed increased left anterior hippocampal activations in the extended visual compared with the maintenance condition. Onthesubsequent probeinterval, however, older adultsshowed more left and right inferior frontal activations than younger adults. The increased frontal activations at probe in older adults may have been compensatory for the decreased hippocampal activations during maintenance, but alternatively could have reflected the increased difficulty of the probe task for the older subjects. Thus, we demonstrate qualitatively different engagement of both frontal and hippocampal structures in older adults in a working memory task, despite behavioral equivalence.