Abstract
Spontaneous signals in neuroimaging data may provide information on cortical health in disease and aging, but the relative sensitivity of different approaches is unknown. In the present study, we compared different but complementary indicators of neural dynamics in resting-state MEG and BOLD fMRI, and their relationship with blood flow. Participants included patients with post-stroke aphasia, age-matched controls, and young adults. The complexity of brain activity at rest was quantified in MEG using spectral analysis and multiscale entropy (MSE) measures, whereas BOLD variability was quantified as the standard deviation (SDBOLD), mean squared successive difference (MSSD), and sample entropy of the BOLD time series. We sought to assess the utility of signal variability and complexity measures as markers of age-related changes in healthy adults and perilesional dysfunction in chronic stroke. The results indicate that reduced BOLD variability is a robust finding in aging, whereas MEG measures are more sensitive to the cortical abnormalities associated with stroke. Furthermore, reduced complexity of MEG signals in perilesional tissue were correlated with hypoperfusion as assessed with arterial spin labeling (ASL), while no such relationship was apparent with BOLD variability. These findings suggest that MEG signal complexity offers a sensitive index of neural dysfunction in perilesional tissue in chronic stroke, and that these effects are clearly distinguishable from those associated with healthy aging.
Highlights
Cerebrovascular stroke is a common cause of cognitive, language, and motor impairments
In all group-comparison brain maps in this paper, but not for correlation analyses, the color scale represents mean differences in the quantity of interest (e.g., SDBOLD in this case), while the thresholding is based on p-values resulting from a 2-sample t-test between groups
We found that blood oxygen level dependent (BOLD) variability was reliably reduced in older subjects, regardless of stroke, especially in the default mode regions, variability increased in MSE_1–5 MSE_7–20 Delta Theta Alpha Beta SDBOLD MSSDBOLD SampEnBOLD
Summary
Cerebrovascular stroke is a common cause of cognitive, language, and motor impairments. It is generally thought that recovery of function in perilesional areas offers the best prognosis for clinical improvement after stroke (Heiss et al, 1999; Léger et al, 2002; Heiss and Thiel, 2006) This conclusion is supported by recent studies using transcranial magnetic stimulation (TMS), which have shown improved language performance after inhibitory stimulation to certain contralesional right hemisphere (RH) regions (Naeser et al, 2005, 2010; Winhuisen et al, 2007; Hamilton et al, 2011), or excitatory stimulation to the preserved left hemisphere (LH) cortex adjacent to the lesion (Baker et al, 2010; Fiori et al, 2011). Assessing the functionality of these areas using noninvasive methods is essential to tracking recovery and targeting interventions
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