When we gather new impressions, the first seconds can already give insight into whether we will be able to remember what we have perceived, and if so, how easily. Regardless of whether we are encoding a word in a different language, a face, or a shopping list, the brain translates all of these stimuli into a pattern of neuronal activity that serves as the basis of learning and memory.
The neuronal patterns elicited by different sensory perceptions can resemble each other or be completely different from each other. Previous studies and theories of aging research indicate that neuronal patterns become less distinct in old age. This increasing similarity or “dedifferentiation” of brain activity was taken to be a potential cause of declining memory performance. Other studies, however, show that greater pattern similarity can make it easier to retrieve memory content. In order to better understand these mixed findings, researchers at the Max Planck Institute for Human Development in Berlin examined younger and older adults using electroencephalography (EEG) and analyzed the EEG data using advanced methods.
The result was surprising: The direction of the association between pattern similarity and memory performance clearly differed between younger and older adults. In younger adults, greater pattern distinctiveness was linked to better memory performance. In older participants, the opposite was the case: They were better at retrieving those impressions whose neuronal patterns resembled each other.
For the study, 50 younger participants aged 19 to 27 years and 63 older participants aged 63 to 75 years were asked to memorize presented word–image pairs. They were then shown the images alone to test their memory for the associated words. Throughout the experiment, the participants’ neuronal activity was recorded via EEG. These measurements were used to capture the neuronal processes during the participants’ encoding of the word–image pairs and to represent them as patterns resolved to the millisecond.
Using sophisticated analytical methods, the study’s authors compared each participant’s EEG patterns of those word–image pairs that s/he was able to remember well with the EEG patterns of those s/he did not remember. The older participants mainly retained those pairs in memory whose EEG patterns resembled each other. In contrast, younger participants could best remember the pairs eliciting clearly distinguishable patterns.
“From previous cognitive aging studies, we know that the distinctiveness of neuronal patterns in older adults is lower than in younger adults. We have gone a step further and examined how pattern similarity and memory performance are linked in old age. By doing so, we are making an important contribution to research on memory and cognitive aging,” says Verena R. Sommer, PhD student at the Max Planck Institute for Human Development and the article’s first author.
A potential explanation for the observed age differences is provided by the temporal trajectories of neuronal activity during memorization of the image–word pairs. For the older participants, pattern similarity within the first second of seeing the pairs was decisive for later memory. For the younger adults, pattern distinctiveness at a later point in time of observation was predictive of memory performance. It appears that during encoding younger adults gradually bring processes to bear that make sensory perceptions differentiable in a memory-effective manner.
“We assume that younger people concentrate on unique details during encoding and that this leads to differentiated neuronal patterns for each pair. In contrast, older adults focus on the general impression, which leads to similar neuronal patterns,” says Myriam C. Sander, research scientist and head of the ConMem project, which examines memory processes across the lifespan at the Max Planck Institute for Human Development. The scope of these considerations will now be tested in follow-up studies.
Max Planck Institute for Human Development
The Max Planck Institute for Human Development in Berlin was founded in 1963. It is an interdisciplinary research institution dedicated to the study of human development and education. The Institute belongs to the Max Planck Society for the Advancement of Science, one of the leading organizations for basic research in Europe.
Sommer, V. R., Fandakova, Y., Grandy, T. H., Shing, Y. L., Werkle-Bergner, M., & Sander, M. C. (2019). Neural pattern similarity differentially relates to memory performance in younger and older adults. Journal of Neuroscience, 39(41), 8089–8099. doi:10.1523/JNEUROSCI.0197-19.2019