A New Measure for Neural Compensation Is Positively Correlated With Working Memory and Gait Speed

Neuroimaging studies suggest that older adults may compensate for declines in brain function and cognition through reorganization of neural resources. A limitation of prior research is reliance on between-group comparisons of neural activation (e.g., younger versus older), which cannot be used to assess compensatory ability quantitatively. It is also unclear about the relationship between compensatory ability with cognitive function or how other factors such as physical exercise modulates compensatory ability. Here, we proposed a data-driven method to semi-quantitatively measure neural compensation under a challenging cognitive task, and we then explored connections between neural compensation to cognitive engagement and cognitive reserve. Functional and structural magnetic resonance imaging scans were acquired for twenty-six healthy older adults during a face-name memory task. Spatial independent component analysis (ICA) identified visual, attentional, and left executive as core networks. Results show that the smaller the volumes of the gray matter structures within core networks, the more networks were needed to conduct the task (r=-0.408, p=0.035). Therefore, the number of task-activated networks controlling for the gray matter volume within core networks was defined as a measure of neural compensatory ability. We found that compensatory ability correlated with working memory performance (r=0.528, p=0.035). Among subjects with good memory task performance, those with higher cognitive reserve used fewer networks than subjects with lower cognitive reserve. Among poor-performance subjects, those using more networks had higher cognitive reserve. Our results indicated that using a high cognitive-demanding task to measure the number of activated neural networks could be a useful and sensitive measure of neural compensation in older adults.