Healthy aging entails reorganization of function in prefrontal brain areas

Researchers from HSE University and York University have become the first to analyse the results of 82 functional neuroimaging studies on working memory mechanisms in different adult age groups. The meta-analyses showed that across studies the agreement of various areas of the prefrontal cortex decreases with ageing, suggesting reorganization of brain function during healthy aging. The results have been published in the paper ‘Meta-analyses of the n-back working memory task: fMRI evidence of age-related changes in prefrontal cortex involvement across the adult lifespan’: https://doi.org/10.1016/j.neuroimage.2019.03.074

Working memory is a system that helps keep information readily available as we use it for performing tasks here and now, including complex intellectual operations such as learning, understanding and reasoning. For example, we use this type of memory to detect and remember the most important things in another person’s speech and then give that person a meaningful answer. The resources of working memory are limited, and with age, its size changes.

Marie Arsalidou, Zachary Yaple, and Dale Stevens analysed data on brain activity in 2020 adults, divided into three age groups: young (18-35), middle-aged (35-55), and older adults (55-85). In all the studies, research volunteers played a game called the ‘n-back task’: they were asked to detect and respond whether they had seen the image demonstrated at the moment, ‘n’ positions back. The complexity of the task depends on the value of ‘n’. During an experiment, each study monitored the brain areas that are activated using functional magnetic resonance imaging (fMRI).

Meta-analysis demonstrated that the involvement of prefrontal cortex areas and their coordination during a task showed increased agreement across studies in young people, lower agreement in middle-aged adults, and no significant agreement in older adults. Lack of agreement in older adults suggests increased variability and individual differences in this group. With older age, parietal regions of the cortex are activated more often, which might be a sign of functional re-organization of working memory mechanisms or of these regions’ compensatory function.

The prefrontal cortex plays a key role in complicated intellectual processes, including the coordination of different brain areas that are activated during the use of working memory.

‘Brain changes throughout adulthood, and it appears to be more dynamic that we initially thought. Because the original studies did not consistently report performance scores, we analysed brain responses with the assumption that working memory performance was comparable. Therefore, we cannot say from our study that working memory skills decrease with age. What we can say is that variability in prefrontal cortex activity may suggest differences in strategies used to problem solve across adulthood. This gives a good target for future work to decipher direct relations among age, brain function and performance’ believes one of the study’s authors, Marie Arsalidou, Assistant Professor at the HSE School of Psychology.

The results of this study are comparable with the conclusions of the previous meta-analysis of working memory mechanisms in children, which was carried out by Marie Arsalidou together with HSE researcher Zachary Yaple: during n-back task performance, not only prefrontal and parietal cortex regions are activated in children, but also other brain areas. Further research in this area will help us understand how working memory mechanisms change during development in humans.

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