MRI Study Of Changes In Resting-state Brain Networks Related To Aging

Background Functional MRI indirectly reflect brain activitiessupporting cognition, sensory, motor and so on, by the way of bloodoxygen level depend (BOLD). Brain networks organized by spatialdistance brain regions with fMRI signals of synchronic low frequencyfluctuations mean they could function cooperatively. Age-relatedhigh-order brain functions such as memory, attention, problem solving aswell as sensorimotor ability may alter at different degree, the intrinsicbrain networks underlying the brain functions remain largely unclear,aging-related changes in aging brain should be investigated further.Objective Intrinsic brain activity in a resting state incorporatescomponents of the task negative network called default mode network(DMN) and task-positive networks called attentional networks.Attentional function impairment is one of the major clinicalmanifestations in elderly people. Anti-correlation is a critical feature ofbrain networks. In the present study, the subnetworks of DMN and theircorresponding anti-correlated networks were compared between the eldergroup and young group to investigate the differences of the intrinsic brainactivity. Another aim of our study was to investigate the patterns of alterations in the large-scale brain networks with aging progress,including default mode network (DMN), executive-control network(ECN), dorsalattentional network (DAN) and salience network; we areespecially concerned of the degree to which the large-scale intrinsicnetworks disruted respectively.Methods Two groups of healthy subjects including18young and22older adults were performed resting-state functional magnetic resonanceimaging (fMRI) scanning with a blood oxygen level dependent sensitivesequence (BOLD). All the subjects were normal in the neuropsychologytest with MMSE scores ranged from28to30. Four network componentsof positive and negative correlations were extracted based on seedregions of posterior cingulate cortex (PCC) and ventromedial prefrontalcortex (vMPFC) from the fMRI data, respectively. The fMRI data wereprocessed by international widely used software. Four canonicalresting-state networks including the DMN, ECN, DAN and saliencenetwork were determined by employing seed-based temporal analysis.The visual network was used as control. Connectivity maps werecompared between groups by using two-sample t tests with a thresholdadjustment method based on Monte-Carlo simulations correction at avoxelwise p<0.05.Results Characteristics of decreased functional connectivity in both ofpositive and negative subetworks of the DMN were found in the older group. The traditional regions involved in the DMN showed significantconnectivity decrease. Changes of PCC negative correlations map andvMPFC negative correlations map presented different patterns indistribution. The vMPFC negative network displayed attenuated activitymainly in midline regions (mainly containing supplementary motor area,SMA), whereas the PCC negative network demonstrated decreasedactivity in the regions of lateral fronto-parietal areas.We found that distinct disruptive alterations presented in thelarge-scale aging-related resting brain networks. That is, the DMN wasimpaired the mostly, followed by the DAN and ECN, the saliencenetwork showed minimally functional connectivity disruption. For theelderly group, network volumes reduced by14.9%,7.9%,4.6%and1.6%when compared with each of unified mask for DMN, DAN, ECN and SN,respectively. The visual network was used as control measurement of thehigh order networks, and was found equivalently preserved as control.Voxel based morphology (VBM) analysis indicated extensive braingray matter atrophy in lateral and medial frontal lobe, temporal lobe andparts of parietal lobe, whereas the volume of the parieto-occipital loberelatively preserved in the aged subjects.Conclusions The decreased functional connectivity in brain networks inthe old group may reflect impairments of cognitive functions evenwithout any task load or stimuli. Degeneration of brain in normal people altered organizationally a level of networks. Our findings suggested theaged brain is characterized of selective vulnerability in large-scale brainnetworks. The findings could help for understanding the degenerationmechanism in aging brain. Resting-state fMRI could be an importantnon-invasive tool for investigating the mechanisms in aging brain.