Frequencies Contributing to Functional Connectivity in the Cerebral Cortex in "Resting-state" Data
Dietmar Cordesa,
Victor M. Haughtona,
Konstantinos Arfanakisa,
John D. Carewa,
Patrick A. Turskia,
Chad H. Moritza,
Michelle A. Quigleya and
M. Elizabeth Meyeranda
a From the Departments of Medical Physics (D.C., K.A., J.D.C., P.A.T., M.A.Q., M.E.M.) and Radiology (V.M.H., C.H.M.), University of Wisconsin at Madison.
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FIG 1. Consecutive coronal fMR maps of voxels activated by a text-listening task (top) and of the voxels functionally connected with a 2 x 2-seed voxel ROI (crosshairs) within the auditory cortex during resting-state (bottom). Task activation is evident in the region of the primary and association auditory cortices in the superior temporal lobe. Many of the voxels functionally connected with the seed voxels in the left auditory cortex (crosshairs) have a similar distribution. All maps are representative and are from a single subject. The color scale for the task-activation map refers to z scores (red z, 3.5; yellow z, 5.5), and that for the resting-state map refers to correlation coefficients (red, 0.5; yellow, 0.7). The MR pulse sequence parameters are 2000/50/82 (TR/TE/flip angle) for fMR and 400/50/50 for fcMR.FIG 2. Consecutive coronal images showing task activation for the visual task (top) and connectivity for the visual cortex in resting-state (bottom). The task produces activation in the striate cortex region. The voxels with connectivity to the seed voxel (crosshairs) appear to lie in similar locations in the striate cortex region. The color scale for the task-activation map refers to z scores (red z, 3.5; yellow z, 5.5), and that for the resting-state map refers to correlation coefficients (red, 0.6; yellow, 0.8). The MR pulse sequence parameters are as in figure 1.FIG 3. A selected coronal fMR map of voxels activated by the bilateral finger-tapping task (top) and of voxels functionally connected to an ROI of 2 x 2-seed voxels (crosshairs) in the sensorimotor cortex in a resting acquisition (bottom). The sensorimotor cortex is identified in both the fMR and the fcMR imaging. Not shown are voxels within the dentate nucleus of the cerebellum that were identified with fMR but not with the functional connectivity study. The color scale for the task-activation map refers to z scores (red z, 3.5; yellow z, 5.5), and that for the resting-state map refers to correlation coefficients (red, 0.62; yellow, 0.8). The MR pulse sequence parameters are as in figure 1
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FIG 4. A selected axial fMR map of voxels activated by the bilateral finger-tapping task (top) and of the voxels functionally connected to an ROI of 2 x 2-seed voxels (crosshairs) in the sensorimotor cortex in a resting-state acquisition (bottom). The sensorimotor cortex is identified in both the fMR and the fcMR maps. The SMA is not activated by the paradigm, but connectivity is clearly seen. The color scale for the task-activation map refers to z scores (red z, 3.5; yellow z, 5.5), and that for the resting-state map refers to correlation coefficients (red, 0.62; yellow, 0.8). The MR pulse sequence parameters are as in figure 1
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FIG 5. Spectral analysis of the average correlation coefficient for interregional connectivity in the auditory cortex (same subject illustrated in figure 1). Only frequency components between 0 and 0.05 Hz contribute significantly to the correlation coefficient.FIG 6. Spectral analysis of the average correlation coefficient for interregional connectivity in the striate cortex (same subject illustrated in figure 2). Only frequency components less than 0.05 Hz contribute significantly to the correlation coefficient
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FIG 7. Spectral analysis of the average correlation coefficient for interregional connectivity in the motor cortex (same subject illustrated in figure 3). Only the same low-frequency components contribute significantly to the correlation coefficient.FIG 8. Spectral analysis of the average correlation coefficient obtained using a seed voxel in the right internal carotid artery. Low frequencies do not predominate. The main peak occurs at the cardiac frequency (0.93 Hz); the first harmonic is aliased to 0.65 Hz. A respiratory band is seen at 0.2 Hz
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FIG 9. Spectral analysis of the average correlation coefficient from a seed voxel in the left jugular vein. Note the spread over many frequencies up to 0.4 Hz and the cardiac peaks at 0.93 Hz and 0.65 Hz.FIG 10. Spectral analysis of the average correlation coefficient obtained using a seed voxel in the left ventricle. Note the spread over many frequencies. The cardiac bands show a large spread compared with other tissue. Low-frequency peaks are visible at 0.03 Hz
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FIG 11. Contribution of low frequencies (0 to 0.1 Hz), respiratory frequencies (0.1 to 0.5 Hz), and cardiac frequencies to the cross-correlation coefficient in different ROIs in the same subject. Low-frequency components clearly dominate, contributing to functional connectivity in auditory, visual, and motor cortices. For blood vessels and cerebrospinal fluid, low-frequency components are present, but cardiac and respiratory noise sources are the main contributors
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