Abstract
Substantial evidence indicates that cognitive training can be efficacious for older adults, but findings regarding training-related brain plasticity have been mixed and vary depending on the imaging modality. Recent years have seen a growth in recognition of the importance of large-scale brain networks on cognition. In particular, task-induced deactivation within the default mode network (DMN) is thought to facilitate externally directed cognition, while aging-related decrements in this neural process are related to reduced cognitive performance. It is not yet clear whether task-induced deactivation within the DMN can be enhanced by cognitive training in the elderly. We previously reported durable cognitive improvements in a sample of healthy older adults (age range = 60–75) who completed 6 weeks of process-based object-location memory training (N = 36) compared to an active control training group (N = 31). The primary aim of the current study is to evaluate whether these cognitive gains are accompanied by training-related changes in task-related DMN deactivation. Given the evidence for heterogeneity of the DMN, we examine task-related activation/deactivation within two separate DMN branches, a ventral branch related to episodic memory and a dorsal branch more closely resembling the canonical DMN. Participants underwent functional magnetic resonance imaging (fMRI) while performing an untrained object-location memory task at four time points before, during, and after the training period. Task-induced (de)activation values were extracted for the ventral and dorsal DMN branches at each time point. Relative to visual fixation baseline: (i) the dorsal DMN was deactivated during the scanner task, while the ventral DMN was activated; (ii) the object-location memory training group exhibited an increase in dorsal DMN deactivation relative to the active control group over the course of training and follow-up; (iii) changes in dorsal DMN deactivation did not correlate with task improvement. These results indicate a training-related enhancement of task-induced deactivation of the dorsal DMN, although the specificity of this improvement to the cognitive task performed in the scanner is not clear.
Highlights
While normal aging is accompanied by cognitive declines in processing speed, working memory, episodic memory, and reasoning (Park et al, 2002; Salthouse, 2009), promising evidence indicates that the cognitive system demonstrates plasticity across the entire life span (Hertzog et al, 2008) and that cognitive training can improve performance in many of these domains in older adults (Karbach and Verhaeghen, 2014; Chiu et al, 2017)
A previously published randomized controlled cognitive training trial from our laboratory targeted an episodic memory process involving the formation of object-location associations, which is significantly impaired in old age (Kessels et al, 2007; Old and NavehBenjamin, 2008)
We evaluate whether these training-related behavioral gains were accompanied by changes in neural activity in an important large-scale network
Summary
While normal aging is accompanied by cognitive declines in processing speed, working memory, episodic memory, and reasoning (Park et al, 2002; Salthouse, 2009), promising evidence indicates that the cognitive system demonstrates plasticity across the entire life span (Hertzog et al, 2008) and that cognitive training can improve performance in many of these domains in older adults (Karbach and Verhaeghen, 2014; Chiu et al, 2017). While the evidence for training-related improvements in brain structure (e.g., white matter integrity, cortical thickness) is rather limited in older adults (Boyke et al, 2008; Engvig et al, 2012, 2010; Lövdén et al, 2012), changes in neural activity have been more commonly observed (Park and Bischof, 2013). Cognitive training has been associated with increased intra-network connectivity in the DMN, frontoparietal network (FPN), and salience network (Cao et al, 2016; De Marco et al, 2016), and with increased anti-correlation between the task-negative DMN and the task-positive FPN (Cao et al, 2016; Lebedev et al, 2018)
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