Memory Specificity is Linked to Repetition Effects in Event-Related Potentials Across the Lifespan

• In Event: Attention and memory in infants and children

Abstract

Our memories depend on our brain’s ability to form internal representations of relevant aspects of the world that can later be retrieved. The specificity with which past experiences can be remembered varies across the lifespan, possibly due to differences in how precisely information is encoded. This memory formation can be investigated through repetition effects, the common finding that neural activity is altered (suppressed or enhanced) when stimuli are repeated. However, whether differences in this indirect measure of memory formation relate to lifespan age differences in memory specificity has not yet been established. In the present electroencephalography study, we examined repetition effects in event-related potentials and their relation to recognition specificity in 21 children (aged 7–9 years), 39 young adults (18–30 years), and 55 older adults (65–76 years). During incidental encoding, participants viewed repeated object images from different categories. During subsequent recognition, old, similar (lure), and new objects were presented, allowing for a differentiation of memory for the general category versus the specific item including lure discrimination. A shorter version of the task was used for the children as well as an additional behavioral control sample of 23 young adults. Overall, when accounting for the differences in task difficulty, the age pattern in memory performance shows that 7–9-year-old children already show adult-like levels of item-specific recognition and lure discrimination. Further, aggregated performance measures did not show differences between young and older adults while individual elements of the measures (e.g., lure discrimination) did, indicating aging-related behavioral disparity in specific memory aspects.
Using non-parametric cluster-based permutation analysis, we derived group-specific time–electrode clusters that indicate the trial time points and electrodes in which first and second object presentations during encoding showed reliable differences. We identified neural repetition suppression effects in all age groups, and repetition enhancement for adults (see Figure 1). The magnitudes of the repetition suppression effects differed between age groups, with children showing larger effects than adults, while younger and older adults did not differ in either their suppression nor enhancement effects (Figure 2 left). Furthermore, inter-individual differences in the magnitude of the neural repetition effects were positively associated with differences in item recognition performance but not mere category recognition (Figure 2 right). In line with the hypothesis that these repetition-related activation differences reflect the formation of memory representations, across groups, individuals exhibiting larger repetition effects during encoding showed better item recognition memory than individuals with smaller repetition effects did. Importantly, this was not due to overall age group differences but the association remained when age differences were eliminated by standardizing the measures within groups. Furthermore, the brain–behavior associations did not significantly differ between the groups, suggesting largely common neural correlates of successful memory encoding across the lifespan.
In sum, our findings demonstrate that neural repetition effects reflect encoding mechanisms that facilitate the formation of highly specific memory representations and highlight their significance as a neural indicator of individual differences in episodic memory encoding across the lifespan.

Authors

• Verena R. Sommer, Max Planck Institute for Human Development
  Presenting Author

• Luzie Mount, TU Dortmund University
  Non-Presenting Author

• Sarah Weigelt, TU Dortmund University
  Non-Presenting Author

• Markus Werkle-Bergner, Max Planck Institute for Human Development
  Non-Presenting Author

• Myriam Sander, Max Planck Institute for Human Development
  Non-Presenting Author