Frequency-resolved dynamic functional connectivity and scale-invariant connectivity-state behavior
Description
Investigating temporal variability of functional connectivity is an emerging field in connectomics. Entering dynamic functional connectivity by applying sliding window techniques on resting-state fMRI (rs-fMRI) time courses emerged from this topic. We introduce frequency-resolved dynamic functional connectivity (frdFC) by means of multivariate empirical mode decomposition (MEMD) followed up by filter-bank investigations. We develop our method on the most canonical form by applying a sliding window approach to the intrinsic mode functions (IMFs) resulting from MEMD. We explore two modifications: uniform-amplitude frequency scales by normalizing the IMFs by their instantaneous amplitude and cumulative scales. By exploiting the well established concept of scale-invariance in resting-state parameters, we compare our FRDFC approaches. In general, we find that MEMD is capable of generating time courses to perform frdFC and we discover that the structure of connectivity states is robust over frequency scales and even becomes more evident with decreasing frequency. This scale-stability varies with the number of extracted clusters when applying K-means. We find a scale-stability drop-off from k = 4 to k = 5 extracted connectivity states, which is corroborated by null models, simulations, theoretical considerations, filter banks, and scale-adjusted windows. Our filter-bank studies show that filter design is more delicate in the rs-fMRI than in the simulated case. Besides offering a baseline for further FRDFC research, we suggest and demonstrate the use of scale-stability as a quality criterion for connectivity-state and model selection. We present first evidence showing that scale-invariance plays an important role in connectivity-state considerations. A data repository of our frequency-resolved time series is provided.
Resources
| Name |
Format |
Description |
Link |
|
57 |
|
https://epub.uni-regensburg.de/32642/3/rs.zip |
|
74 |
|
https://epub.uni-regensburg.de/32642/1/README.txt |
|
74 |
|
https://epub.uni-regensburg.de/32642/5/indexcodes.txt |
|
57 |
|
https://epub.uni-regensburg.de/32642/4/simulated.zip |