I apply a detrended fluctuation analysis (DFA) to rs-fMRI signal before and after some task. Certain areas show an increase in Hurst exponent in after-task activity in comparison to the initial state. I have found a few articles which report about a decrease of DFA index in a task (like here https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3197021/) and a decline have been explained as the growth of cognitive efforts.
But how can be explained an increase from a functional and cognitive point of view? Maybe exist an article related to this case on EEG or MEG data, that I did not find?
Dear Alina,
The Hurst exponent 0 1 above, since you specifically asked about "increase of Hurst exponent" (note that an increase to 0.5 can only occur from H being in the open interval (0, 0.5) and the interpretation would be as "transition from mean-reverting state to uncorrelated state"). It would have been helpful to know in which ranges your Hurst exponent values are found.
I hope that my comments may have been helpful. If not, please let me know and we may reason together.
Best, Hans
P.S.: As for your question about how an increase should be interpreted from a cognitive point of view, I would spontaneously think of *learning* in the sense of a persistent pattern getting established.
I think it's important to identify what question you are trying to answer by applying DFA to your time series. Are you interested the temporal structure of the fluctuations in you rs-FMRI signal? If so, why? What information might examining DFA or other related measures uncover? I generally use DFA to examine the dynamical structure of gait fluctuations and how this variability relates to human motor control processes. Changes in the DFA exponent may arise for many reasons. DFA is just a measure of the average correlation structure of a time series. Changes in the scaling exponent can mean different things depending on what you are measuring and what context those measurements were taken in. I hope this was helpful. If you can provide a bit more information about what you are studying, I will do my best to help out.
I have found the same increase with EDA/GSR data! I wonder what your interpretation is!
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