Default-mode network activity distinguishes Alzheimer's disease from healthy aging: Evidence from functional MRI

Abstract

Recent functional imaging studies have revealed coactivation in a distributed network of cortical regions that characterizes the resting state, or default mode, of the human brain. Among the brain regions implicated in this network, several, including the posterior cingulate cortex and inferior parietal lobes, have also shown decreased metabolism early in the course of Alzheimer's disease (AD). We reasoned that default-mode network activity might therefore be abnormal in AD. To test this hypothesis, we used independent component analysis to isolate the network in a group of 13 subjects with mild AD and in a group of 13 age-matched elderly controls as they performed a simple sensory-motor processing task. Three important findings are reported. Prominent coactivation of the hippocampus, detected in all groups, suggests that the default-mode network is closely involved with episodic memory processing. The AD group showed decreased resting-state activity in the posterior cingulate and hippocampus, suggesting that disrupted connectivity between these two regions accounts for the posterior cingulate hypometabolism commonly detected in positron emission tomography studies of early AD. Finally, a goodness-of-fit analysis applied at the individual subject level suggests that activity in the default-mode network may ultimately prove a sensitive and specific biomarker for incipient AD.

Male‐to‐female gender dysphoria: Gender‐specific differences in resting‐state networks

“…An in‐house MATLAB script, which was based on protocols of the previous studies (Clemens, Jung, et al., 2014; Clemens, Voss et al., 2014; Greicius, 2008; Greicius, Srivastava, Reiss, & Menon, 2004; Mingoia et al., 2012) was used to select those components optimally representing the individual functional networks. From the paper by Smith et al.…”

Molecular Brain Imaging in the Multimodality Era

“…The default network is active when engaged in internally focused tasks including autobiographical memory retrieval, envisioning the future, and conceiving the perspectives of others, with an MTL subsystem and a medial prefrontal subsystem that converge on important nodes of integration (Buckner et al, 2008). This network includes posterior cingulate and parietal lobe (Buckner, 2004(Buckner, , 2005Greicius et al, 2003Greicius et al, , 2004Wang et al, 2006). Greicius et al (2004) reported decreased default mode network activity in posterior cingulate and hippocampus of AD subjects that suggested disrupted connectivity between these areas.…”

A method for independent component graph analysis of resting‐state fMRI

“…The ICA‐generated volumetric maps are generally reported as z ‐scores in order to show the contribution of each component's time‐course to the BOLD signal in each voxel. These maps are then commonly analyzed in a voxel‐wise manner in order to show between or within‐group connectivity differences (Greicius, Srivastava, Reiss, & Menon, 2004). The number of components is generally user‐defined and many of the resulting components may be due to non‐neuronal activity (such as cardiovascular signal, eye movements, muscle activity in the vicinity of the head and head movement).…”