Abstract
Healthy aging is accompanied by working memory-related functional cerebral changes. Depending on performance accuracy and the level of working memory demands, older adults show task-related patterns of either increased or decreased activation compared to younger adults. Controversies remain concerning the interpretation of these changes and whether they already manifest in earlier decades of life. To address these issues, functional magnetic resonance imaging (fMRI) was used to examine brain activation during spatial working memory retrieval in 45 healthy individuals between 20 and 68 years of age. Participants performed a modified version of the Corsi Block-Tapping test (CBT). The CBT requires the storage and subsequent reproduction of spatial target sequences and allows modulating working memory load by a variation of sequence length. Results revealed that activation intensity at the lowest CBT load level increased with increasing age and positively correlated with the number of errors. At higher CBT load levels, activation intensity decreased with increasing age together with a disproportional accuracy decline on the behavioral level. Moreover, results suggests that younger individuals showed higher activation intensity at high CBT load than at low CBT load switching to the opposite pattern at an age of about 40 years. Consistent with the assumptions of the Compensation-Related Utilization of Neural Circuits Hypothesis (CRUNCH), the present results reveal specific age-related alterations in left dorsolateral prefrontal cortex activation in response to increasing task load. Specifically, the results point toward increasing neural inefficiency with age at low task load and a progressive limitation of resources with age at higher task load. The present findings argue for an increasing functional cerebral dysfunction over a time span of 50 years that may partly be compensated on the behavioral level until a resource ceiling is approached.
Highlights
Since our environment provides a huge complexity of spatial information, we constantly need to adapt our spatial memory system
Since the present study focused on agerelated changes during spatial working memory retrieval, only the retrieval regressors were further analyzed
Analysis of local blood oxygenation level dependent (BOLD) signal changes using an independent region of interest (ROI) within left dorsolateral prefrontal cortex indicated how the direction of age-related activation differences varied depending on the level of working memory load: At higher load levels, activation intensity decreased with increasing age
Summary
Since our environment provides a huge complexity of spatial information, we constantly need to adapt our spatial memory system. Thereby, we have to encode, maintain, update, and recall spatial information, as well as preserve these processes from distraction Efficient coordination of these processes depends on intact spatial working memory operations which find their neural substrate in a complex anterior-posterior network of posterior parietal, premotor, and prefrontal brain regions (Cabeza and Nyberg, 2000; Hartley and Speer, 2000; Rottschy et al, 2012). The hippocampus plays a major role for object-location associations and positional memory (Kessels et al, 2001; Bird and Burgess, 2008) while cerebellar brain regions are associated with sequential information processing (Leggio et al, 2008; Tedesco et al, 2011). Whereas ventrolateral parts are involved in the maintenance of information, dorsolateral prefrontal activation reflects working memory
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