Abstract
Research has shown the human brain is organized into separable functional networks during rest and varied states of cognition, and that aging is associated with specific network dysfunctions. The present study used functional magnetic resonance imaging (fMRI) to examine low-frequency (0.008 < f < 0.08 Hz) coherence of cognitively relevant and sensory brain networks in older adults who participated in a 1-year intervention trial, comparing the effects of aerobic and non-aerobic fitness training on brain function and cognition. Results showed that aerobic training improved the aging brain's resting functional efficiency in higher-level cognitive networks. One year of walking increased functional connectivity between aspects of the frontal, posterior, and temporal cortices within the Default Mode Network and a Frontal Executive Network, two brain networks central to brain dysfunction in aging. Length of training was also an important factor. Effects in favor of the walking group were observed only after 12 months of training, compared to non-significant trends after 6 months. A non-aerobic stretching and toning group also showed increased functional connectivity in the DMN after 6 months and in a Frontal Parietal Network after 12 months, possibly reflecting experience-dependent plasticity. Finally, we found that changes in functional connectivity were behaviorally relevant. Increased functional connectivity was associated with greater improvement in executive function. Therefore the study provides the first evidence for exercise-induced functional plasticity in large-scale brain systems in the aging brain, using functional connectivity techniques, and offers new insight into the role of aerobic fitness in attenuating age-related brain dysfunction.
Highlights
By the year 2030 one-fifth of Americans will be 65 years or older, causing health care spending to increase by an estimated 25% (He et al, 2005; CDC, 2007)
This study demonstrated that moderate exercise enhances functional connectivity between regions with age-related disruption in cognitively relevant brain networks
We found that the walking group showed increased connectivity after 12 months in regional connections supporting the Default Mode Network (DMN) and fronto-executive network (FE) systems, in the frontal and temporal cortices, while the FTB group showed increased connectivity in regions of the DMN and the FP system at 6 and 12 months, respectively
Summary
By the year 2030 one-fifth of Americans will be 65 years or older, causing health care spending to increase by an estimated 25% (He et al, 2005; CDC, 2007). Advancing age has the greatest impact on structural integrity of the frontal and medial temporal cortices and progressively lesser impact on posterior brain regions such as the parietal and occipital cortices (O’Sullivan et al, 2001; Raz et al, 2005; Davis et al, 2009; Fjell et al, 2009) This corresponds to disruption in brain networks that depend on efficient communication in the prefrontal cortex (Colcombe et al, 2005; Persson et al, 2006), and pathways between the frontal and posterior cortices (AndrewsHanna et al, 2007; Thomas et al, 2008). Studies show aging is associated with altered fronto-temporal activation patterns compared to young adults during hippocampal-dependent tasks, such that older adults tend to have more fronto-temporal activation compared to younger adults who co-activate the hippocampus with regions involved in the perceptual representation of to-be remembered stimuli (Grady et al, 2003; Dennis et al, 2008). The frontal cortex plays a prominent role in cognitive aging, and interventions that target improved communication and Frontiers in Aging Neuroscience www.frontiersin.org
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