Brain task-negative networks (default mode network, DMN) and task-positive networks appear to operate
largely in opposition, such that task-negative networks show activation during resting states, whilst task-positive networks
are deactivated with the reverse being true during goal-oriented behavior. Altered DMN and task-positive network activity
has been observed in amnestic mild cognitive impairment (aMCI) subjects. However, no study has directly linked the patterns
of between-state differences in the same aMCI cohort regarding these two types of functional networks. The spatial
and temporal characteristics of intrinsic, low frequency BOLD signal fluctuations both during resting state and episodic
memory fMRI task were assessed in 28 aMCI subjects and 23 matched healthy controls, using a posterior cingulate cortex-
based temporal correlation analysis. aMCI subjects showed impaired attenuation in the DMN between rest and task
state, and greater cognitive impairment was associated with decreased ability to attenuate DMN during task engagement.
Moreover, more redistributed resource from DMN appeared to be required in aMCI to maintain the similar task performance
possibly to offset their inability to engage task-positive networks. In order to complete a given task, mobilized and
redistributed resources of DMN appeared to replace task-positive network function to some degrees in aMCI subjects.
This may represent an inability to control the switching of functional modes between these types of network.
Keywords: Amnestic mild cognitive impairment, Alzheimer’s disease, default mode network, functional magnetic resonance
imaging, functional connectivity, task-positive network, CFT, DMN
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