The functional interaction of the brain default network with motor networks is modified by aging

Motor disturbance is a major source of injury in older adults, a fact facilitated by the interfering action of cognitive activities on ongoing motor tasks. The present work studies the influence of aging on the functional interaction of the default mode network(DMN) and two key networks for motion, the somato-motor network(SMN) and the posterior motor circuit of basal ganglia(BGmC). The relationship between these networks was explored in young (31.3 ± 5.2;n = 12) and aged (58.7 ± 5.4;n = 15) groups by studying the co-activation (positive correlation)/co-inactivation (negative correlation) and unrelated fluctuations (no significant correlation) of the BOLD-signals recorded by functional magnetic resonance imaging in the motor/somatosensory primary cortex, basal ganglia(BG) centers, and the posterior cingulate cortex(DMN) which projects to the SMN and BGmC. Two experimental conditions were used, one with subjects performing hand movements (a condition which should activate the motor networks and block the DMN) and a resting condition with subjects not performing any particular task (a condition where the DMN is recruited and the motor networks should be less active). In the young group, the DMN showed co-inactivation with the SMN and a non-significant correlation with the BGmC. However, in the aged-group the DMN-BGmC co-inactivation decreased (particularly during the motor action), and the DMN-SMN co-inactivation was replaced by a co-activation (during both the resting and motor action). Present data show a marked effect of age on the functional relationship of DMN with these cortical (SMN) and subcortical(BG) motor networks, suggesting that a disorder of the DMN-motor network co-inactivation may facilitate the motor disturbances that often accompany aging.