Scale-Free Functional Brain Networks Exhibit Increased Connectivity, Are More Integrated and Less Segregated in Patients with Parkinson’s Disease following Dopaminergic Treatment

Abstract

Dopaminergic treatment (DT), the standard therapy for Parkinson’s disease (PD), alters the dynamics of functional brain networks at specific time scales. Here, we explore the scale-free functional connectivity (FC) in the PD population and how it is affected by DT. We analyzed the electroencephalogram of: (i) 15 PD patients during DT (ON) and after DT washout (OFF) and (ii) 16 healthy control individuals (HC). We estimated FC using bivariate focus-based multifractal analysis, which evaluated the long-term memory (H(2)) and multifractal strength (ΔH15) of the connections. Subsequent analysis yielded network metrics (node degree, clustering coefficient and path length) based on FC estimated by H(2) or ΔH15. Cognitive performance was assessed by the Mini Mental State Examination (MMSE) and the North American Adult Reading Test (NAART). The node degrees of the ΔH15 networks were significantly higher in ON, compared to OFF and HC, while clustering coefficient and path length significantly decreased. No alterations were observed in the H(2) networks. Significant positive correlations were also found between the metrics of H(2) networks and NAART scores in the HC group. These results demonstrate that DT alters the multifractal coupled dynamics in the brain, warranting the investigation of scale-free FC in clinical and pharmacological studies.

Multiscale Detrended Cross-Correlation Coefficient: Estimating Coupling in Nonstationary Neurophysiological Signals

“…The numerator and denominator of Equation 1 are integral parts of the detrended fluctuation analysis (44) and detrended cross-correlation analysis (45) analysis, respectively. DCCC has been incorporated in surrogate testing of fractal (scale-free) coupling already (12,19,(46)(47)(48).…”

Fractal Parameters as Independent Biomarkers in the Early Diagnosis of Pediatric Onset Inflammatory Bowel Disease

“…Here, a total of 18 grid cell sizes were used to obtain data points for fitting the regression curves to describe the scale-count power law dependence. Specifically, grid cells sized ε ∈ {5, 6,7,8,9,10,12,14,16,18,20,23,27,30,35,40,46, 52} px were used in both the box counting method and the cumulative mass method. Figure 1 shows an example binary image of a nucleus and also illustrates the typical nucleus size and the look of the chromatin texture, covered by grid cells of different sizes, ε.…”

“…In the field of medical science, the concept of fractals has been used for both image [1][2][3][4][5][6][12][13][14] and signal [15][16][17][18] analysis. The fractal feature-based image analysis employed so far in gastroenterology has shown promising results in cancer research [19][20][21][22][23] and has helped in the analysis of wireless capsule endoscopy [24] and colonoscopy images [25].…”