Frequency-Dependent Changes in the Regional Amplitude and Synchronization of Resting-State Functional MRI in Stroke

Abstract

Resting-state functional magnetic resonance imaging (R-fMRI) has been intensively used to assess alterations of inter-regional functional connectivity in patients with stroke, but the regional properties of brain activity in stroke have not yet been fully investigated. Additionally, no study has examined a frequency effect on such regional properties in stroke patients, although this effect has been shown to play important roles in both normal brain functioning and functional abnormalities. Here we utilized R-fMRI to measure the amplitude of low-frequency fluctuations (ALFF) and regional homogeneity (ReHo), two major methods for characterizing the regional properties of R-fMRI, in three different frequency bands (slow-5: 0.01-0.027 Hz; slow-4: 0.027-0.73 Hz; and typical band: 0.01-0.1 Hz) in 19 stroke patients and 15 healthy controls. Both the ALFF and ReHo analyses revealed changes in brain activity in a number of brain regions, particularly the parietal cortex, in stroke patients compared with healthy controls. Remarkably, the regions with changed activity as detected by the slow-5 band data were more extensive, and this finding was true for both the ALFF and ReHo analyses. These results not only confirm previous studies showing abnormality in the parietal cortex in patients with stroke, but also suggest that R-fMRI studies of stroke should take frequency effects into account when measuring intrinsic brain activity.

Frequency‐specific alterations of regional homogeneity in subcortical stroke patients with different outcomes in hand function

“…In addition, several studies (Park et al, 2011;Yin et al, 2014;Yin, Luo, et al, 2013a) have influenced the robustness of their results. Interestingly, we did not find increased ReHo in the parietal cortex in the patient group, which was a primary outcome reported in Zhu's study (Zhu et al, 2015), in the comparisons between the HC group and the patient group (CPH + PPH, 52 patients) in the three frequency bands. Interestingly, we did not find increased ReHo in the parietal cortex in the patient group, which was a primary outcome reported in Zhu's study (Zhu et al, 2015), in the comparisons between the HC group and the patient group (CPH + PPH, 52 patients) in the three frequency bands.…”

“…Third, we explored the correlations between ReHo values at the specific frequency bands and the FMA-HW scores of hand function across all the stroke patients. Based on the typical frequency band studies among stroke subgroups (Yin, Luo, et al, 2013a;Yin et al, 2012Yin et al, , 2014 and a subfrequency study between stroke patients and HCs (Zhu et al, 2015), we hypothesized that spontaneous brain activity following stroke would be influenced by both the specific frequency of LFO and the severity of stroke. We predicted that the results in the typical band would be consistent with those of our previous studies among stroke subgroups, which might be found in the primary sensorimotor cortex, SMA, and several high-order motor regions, such as the frontal gyrus and the parietal lobule.…”

Implication of the Slow-5 Oscillations in the Disruption of the Default-Mode Network in Healthy Aging and Stroke

“…3 and 6). This observation is in accordance with a previous report describing a high susceptibility of those slow-5 oscillations after the event of a stroke and the contribution of those oscillations to the cortical impairment (Zhu et al, 2015).…”

“…6), which is consistent with studies found in the literature (Garrity et al, 2007;Zuo et al, 2010). In contrast, our population of subacute stroke patients displayed a reduction in the amplitude and power that was specific to those slow-5 oscillations, which is consistent with results of a recent report by Zhu et al (2015), where more activity changes were recorded in the ALFF of the slow-5 band. Our observation is coupled with an increase in slow-4 oscillations.…”

“…This modification of oscillation amplitude could have dramatic influences on the balance of intrinsic oscillation, contributing to the functionality and integrity of the DMN network with oscillations in the slow-5 frequency range decreasing in their dominance of the restingstate fluctuations. The repeated identification of slow-5 frequencies in the current study and other previous studies (Calhoun et al, 2011;Han et al, 2011;Yu et al, 2014;Zhu et al, 2015) stresses the critical role of the slow-5 oscillation in network disruption, and it also accentuates the importance of managing slow-5 oscillations in the health of the DMN. More studies are needed to validate the current findings and to determine their possible clinical significance.…”