How does the brain work when you sleep? A key to answer this question is to figure out that the resting state brain functions are 'fractal'. We have developed parsimonious fractal-based methodologies to reveal the functional mechanism of the resting state brain through functional magnetic resonance imaging (fMRI).
A blood oxygen level dependent (BOLD) MRI signals taken at rest tends to exhibit 1/f power-law scaling or temporally long-range dependence called the 'fractality'. In the pioneering project of Leibniz Institute for Neurobiology, we have proposed a computational model of resting state brain activities which describes not only the physical mechanism of fractality in BOLD signals but also the theoretical relationship between fractality and functional connectivity. We finally have suggested a novel method based on wavelets, which allows us to estimate functional connectivity of endogenous neuronal activities hidden beyond the fractality of BOLD signals, and suggested the 'nonfractal connectivity' as a new concept for quantifying brain functional network (IJCNN 2012).
The fractal-based analysis of resting state fMRI had been applied not only to the effects of electric stimulation on resting state functional connectivity in the rat brain, but also to studying resting state brain functions in patients with major depression disorders (MDD) (Dissertation 2013). We were recently involved in an international joint research program for neuroimaging study on autism by cooperating with University of Cyprus (Cyprus), University of Cambridge (UK), and the Hospital for Sick Children (Canada). Using the fractal approach to resting state fMRI, the study showed that a difference in brain functions pertinent to social cognition may be present between male and female with autism (OHBM 2019). We are continuously pursuing to develop new clinical applications of the fractal-based data analysis for a variety of brain diseases including brain tumors, dementia, autism, and so forth.
nonfractal: Nonfractal Connectivity Estimator
long-memory: The MATLAB Toolbox for the Analysis of Long Memory Processes
Dissertation: Long memory model of resting state functional MRI (9/2013)
Conference presentation (IJCNN): Fractal analysis of resting state functional connectivity of the brain (6/2012)
Stavros Trakoshis, Pablo Martínez-Cañada, Federico Rocchi, Carola Canella, Wonsang You, Bhismadev Chakrabarti, Amber N. V. Ruigrok, Edward T. Bullmore, John Suckling, Marija Markicevic, Valerio Zerbi, MRC AIMS Consortium, Simon Baron-Cohen, Alessandro Gozzi, Meng-Chuan Lai, Stefano Panzeri, Michael V. Lombardo, "Intrinsic excitation-inhibition imbalance affects medial prefrontal cortex differently in autistic men versus women," eLife, vol. 9, e55684 (2020).
Wonsang You, Catherine Limperopoulos, "Study on Linear Combination of Long Memory Processes Corrupted by Additive Noises for fMRI Time Series Analysis," bioRxiv 210518, December 2017.
Wonsang You and Jörg Stadler, "Fractal-driven distortion of resting state functional networks in fMRI: a simulation study," Brain Connectivity 2012, Vol.0, No.0, September 2012.
Wonsang You, Sophie Achard, and Jörg Stadler, "Fractal-based linear model of resting state hemodynamic response in fMRI," BMC Neuroscience 2012, 13(Suppl 1):P35, July 2012.
Wonsang You, Sophie Achard, Jörg Stadler, Bernd Brückner, and Udo Seiffert, "Fractal analysis of resting state functional connectivity of the brain," 2012 International Joint Conference on Neural Networks, June 2012. - View presentation.
Wonsang You and Wojciech Kordecki, "A Proof on Asymptotics of Wavelet Variance of a Long Memory Process by Using Taylor Expansion," arXiv:1202.4746, July 2010.
Stavros Trakoshis, Wonsang You, Simon Baron-Cohen, Bhismadev Chakrabarti, Amber Ruigrok, Ed Bullmore, John Suckling, Meng-Chuan Lai, Michael Lombardo, "Endogenous BOLD Signal Complexity of vmPFC is Different Between Autistic Men and Women," The 25th annual meeting of the Organization for Human Brain Mapping, Rome, Italy (June 2019).
Wonsang You, "Fractal-driven distortion of default-mode functional networks in resting state fMRI," Biointelligence Lab, Seoul National University, South Korea (June 20, 2012).
Wonsang You, "Fractal-driven distortion of connectivity and information flow in resting state fMRI time series," Asia Pacific Center for Theoretical Physics, Pohang, South Korea (June 18, 2012).
Wonsang You and Jörg Stadler, "Fractal-based Correlation Analysis for Resting State Functional Connectivity of the Rat Brain in Functional MRI," CBBS Educational Workshop on Resting State fMRI, April 2010.