Open AccessFractality of tics as a quantitative assessment tool for Tourette syndrome
Author(s) -
Payton Beeler,
Nicholas Jensen,
Soyoung Kim,
Amy RobichauxViehoever,
Bradley L. Schlaggar,
Deanna J. Greene,
Kevin J. Black,
Rajan K. Chakrabarty
Publication year - 2022
Publication title -
journal of the royal society interface
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.655
H-Index - 139
eISSN - 1742-5689
pISSN - 1742-5662
DOI - 10.1098/rsif.2021.0742
Subject(s) - tics , tourette syndrome , fractal , fractional brownian motion , psychology , gaussian , statistical physics , chaotic , gaussian noise , mathematics , artificial intelligence , neuroscience , computer science , brownian motion , statistics , physics , mathematical analysis , quantum mechanics , psychiatry
Tics manifest as brief, purposeless and unintentional movements or noises that, for many individuals, can be suppressed temporarily with effort. Previous work has hypothesized that the chaotic temporal nature of tics could possess an inherent fractality, that is, have neighbour-to-neighbour correlation at all levels of timescale. However, demonstrating this phenomenon has eluded researchers for more than two decades, primarily because of the challenges associated with estimating the scale-invariant, power law exponent—called the fractal dimensionD f —from fractional Brownian noise. Here, we confirm this hypothesis and establish the fractality of tics by examining two tic time series datasets collected 6–12 months apart in children with tics, using random walk models and directional statistics. We find thatD f is correlated with tic severity as measured by the YGTTS total tic score, and thatD f is a sensitive parameter in examining the effect of several tic suppression conditions on the tic time series. Our findings pave the way for using the fractal nature of tics as a robust quantitative tool for estimating tic severity and treatment effectiveness, as well as a possible marker for differentiating typical from functional tics.