Inter-individual performance differences in younger and older adults differentially relate to amplitude modulations and phase stability of oscillations controlling working memory contents.

Efficient encoding of relevant information and suppression of irrelevant information influence working memory (WM) performance, which is limited and declines in adulthood. A cued Sternberg WM task and electroencephalographic recordings (EEG) were used to investigate encoding and control operations in response to to-be-remembered (REM) and not-to-be-remembered (NREM) stimuli in younger and older adults. Younger and older adults selectively remembered REM items in a final recognition memory test. During early stages of stimulus processing, inter-trial phase stability was higher for REM than for NREM items in younger and older adults, presumably reflecting preferential encoding of REM items. At later stages, the oscillatory power of oscillations in the alpha/beta frequency range was higher for NREM than for REM, presumably reflecting the inhibitory top-down suppression of task-irrelevant information. Early phase stability was selectively related to working memory performance in younger adults and high-functioning older adults. The results of this study reveal the differential contributions of low-level feature binding and strategic control components to adult age differences in WM, and show that older adults with more youth-like processing dynamics tend to achieve higher levels of performance.