Modulation of the Default-Mode Network Between Rest and Task in Alzheimer's Disease

Abstract

Default-mode network (DMN) connectivity at rest is disrupted in Alzheimer's Disease (AD), but it is unknown whether this abnormality is a static feature, or if it varies across cognitive states. We measured DMN integrity in 16 patients with mild AD and 18 controls during resting state and a simple visual task. Patients showed resting-state deficits in the parahippocampal gyrus and posterior cingulate. No group differences were found during the task. Controls exhibited higher DMN connectivity of multiple regions during rest than task, while the patient group showed no modulation of the DMN between states. However, the relative degree of increased resting- versus task-state co-activation in the posterior cingulate and precuneus was predictive of mini-mental status exam (MMSE) scores in AD patients, while measures at rest or task alone were not associated with MMSE. These findings suggest that a resting state may be more suited to detecting DMN abnormalities in AD than a simple task. However, the degree of state-dependent modulation in the DMN may be a better predictor of the individual cognitive status than a single-state acquisition. This study demonstrates an apparent reduction in the capacity for DMN modulation in individuals with mild AD, the degree of which uniquely predicted cognitive status.

Brain network changes and memory decline in aging

“…These nodes also showed declining covariance strength between the insula and anterior and posterior cingulate nodes, and between the entorhinal cortex and superior temporal gyrus in decliners, while improvers showed increasing (insular) or stable (entorhinal) relationships over time. These findings fit more closely with previous studies of aging and age-related disease particularly in relation to posterior cingulate and temporal lobe connectivity changes (Andrews-Hanna et al, 2007; Campbell, Grigg, Saverino, Churchill, & Grady, 2013; Schwindt et al, 2013; Supekar, Menon, Rubin, Musen, & Greicius, 2008), but the decline in covariance is again noted in during the period of worsening task performance in the decliner group.…”

Shaped by our thoughts – A new task to assess spontaneous cognition and its associated neural correlates in the default network

“…Converging lines of evidence now show that clinical memory measures serve as sensitive and predictive markers of DN integrity in ageing (Ward et al, 2014) and various clinical conditions, including temporal lobe epilepsy (McCormick et al, 2014), and Alzheimer's disease (McLaren, Sperling, & Atri, 2014). In particular, memory and cognition in Alzheimer's disease are not only associated with static impairments in DN connectivity, but also impairments in the flexible modulation of the DN (McLaren et al, 2014;Schwindt et al, 2013). Here, we report a simple, brief task that elicits DN-mediated, predominantly memory-based processes in healthy older individuals.…”

A single session of exercise increases connectivity in sensorimotor-related brain networks: a resting-state fMRI study in young healthy adults

“…While Cohen’s D does not localize sub-regions within an RSN, it is much less computationally intensive than permutation testing and proved to be sensitive to a session effect. This approach may be conducive to compare longitudinal changes in RSNs of interest, like the DMN (Greicius et al, 2004; Tanabe et al, 2011; Schwindt et al, 2013). …”

“…Given the paucity of rs-fMRI exercise literature, we focused on well established RSNs including those potentially related to motor activity. Additionally, two other RSNs were selected, the default mode network (DMN) RSN, for its perceived clinical utility (Schwindt et al, 2013), and the medial visual RSN, as a control. A dual regression technique (Filippini et al, 2009) was used to produce participant/session-specific RSNs.…”