Abstract
The ‘default-mode’ network (DMN) has been investigated in the presence of various disorders, such as Alzheimer’s disease and Autism spectrum disorders. More recently, this investigation has expanded to include patients with ischemic injury. Here, we characterized the effects of ischemic injury in terms of its spectral distribution of resting-state low-frequency oscillations and further investigated whether those specific disruptions were unique to the DMN, or rather more general, affecting the global cortical system. With 43 young healthy adults, 42 older healthy adults, 14 stroke patients in their early stage (<7 days after stroke onset), and 16 stroke patients in their later stage (between 1 to 6 months after stroke onset), this study showed that patterns of cortical system disruption may differ between healthy aging and following the event of an ischemic stroke. The stroke group in the later stage demonstrated a global reduction in the amplitude of the slow-5 oscillations (0.01–0.027 Hz) in the DMN as well as in the primary visual and sensorimotor networks, two ‘task-positive’ networks. In comparison to the young healthy group, the older healthy subjects presented a decrease in the amplitude of the slow-5 oscillations specific to the components of the DMN, while exhibiting an increase in oscillation power in the task-positive networks. These two processes of a decrease DMN and an increase in ‘task-positive’ slow-5 oscillations may potentially be related, with a deficit in DMN inhibition, leading to an elevation of oscillations in non-DMN systems. These findings also suggest that disruptions of the slow-5 oscillations in healthy aging may be more specific to the DMN while the disruptions of those oscillations following a stroke through remote (diaschisis) effects may be more widespread, highlighting a non-specificity of disruption on the DMN in stroke population. The mechanisms underlying those differing modes of network disruption need to be further explored to better inform our understanding of brain function in healthy individuals and following injury.
Highlights
The default-mode network (DMN) is considered a central network of the cortical system
The posterior component of the DMN is disrupted in the stroke-late population, with such reduction of oscillation amplitude in these frequencies potentially disrupting the communication between distal nodes within a system (La et al, 2014; La et al, submitted)
We found that this reduction in slow-5 oscillations may not be exclusive to the DMN, but rather is consistent across different networks following a stroke
Summary
The default-mode network (DMN) is considered a central network of the cortical system. Disruption of DMN network activity/deactivity pattern contributes to the impairment of functional networks associated with a variety of behaviors observed in cognitively impaired populations (Grady et al, 2006, 2010; Persson et al, 2007; Lustig and Jantz, 2014), such as a decline in speed of processing, executive and/or memory functions. This approach is less susceptible to variability in task-related behavior such as motivation and attention
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