Memory Performance is Linked to Neural Repetition Effects Across the Lifespan

Post by Amanda McFarlan

What's the science?

Researchers have long studied neural representations of memories to understand how memories are formed and stored in the brain. One way to do this is by investigating whether neural activity in the brain changes in response to repeated exposure to the same stimuli, known as the repetition effect. Repetition effects can be observed in two different forms: a repetition suppression effect, which occurs when neural activity is lower upon the second presentation of a stimulus, or a repetition enhancement effect, which occurs when neural activity is higher upon the second presentation of a stimulus. This week in Developmental Cognitive Neuroscience, Sommer and colleagues investigated whether memory formation, as measured by neural repetition effects, was associated with memory performance across the lifespan. 

How did they do it?

The authors recruited children (7-9 years), young adults (18-30 years) and older adults (65–76 years) to participate in their study. EEG recordings were acquired for each age group while participants performed an encoding task followed by a recognition task. During the encoding task, participants were shown pictures of objects belonging to different categories (e.g. hats, trees, guitars). The entire encoding task consisted of 720 trials for the adult groups and 360 trials for the children. After completing the encoding task, the authors surprised participants with a recognition task. Participants were not told to memorize the pictures during the encoding task and did not know that they would be tested on their memory. During the recognition task, participants were shown pictures of objects and were asked to identify whether that object was old (an image they had previously seen in the encoding task), similar (an imaging belonging to a category they had previously seen in the encoding task) or new (an image belonging to a novel category). The adult groups completed 480 trials for the recognition task, while the children completed 240.

What did they find?

The authors found that participants in all age groups were able to identify whether an image was old, similar, or new at levels above chance. They showed that children had higher specific item memory (correctly identifying whether an image was old or similar) compared to both adult groups and both children and young adults had a higher lure discrimination index (the difference between images correctly identified as similar and mistaken as old) compared to older adults. However, this finding did not persist after accounting for the fact that children performed an easier and shorter task. Next, the authors examined the EEG recordings to look for changes in neural activity related to repetition effects. They found repetition suppression effects in the posterior, frontal, and central electrode sites for all age groups. They also found a repetition enhancement effect in the frontal and temporal electrode sites for both adult groups as well as in the centro-parietal electrode sites for older adults. The repetition suppression effect (observed in all age groups) and the repetition enhancement effect (observed in adults) were positively correlated with item-specific memory performance.

What’s the impact?

This study shows that item-specific memory performance for all ages is positively correlated with both repetition suppression effects and repetition enhancement effects. This suggests that memory encoding may have similar neural mechanisms in children and adults. Together, these findings provide evidence that neural repetition effects may be a useful neural indicator of memory encoding across the lifespan.

Sommer et. al. Memory specificity is linked to repetition effects in event-related potentials across the lifespan. Developmental Cognitive Neuroscience (2021). Access the original scientific publication here.