The Hurst exponent (H) isolated in fractal analyses of neuroimaging time-series is implicated broadly in cognition. Within this literature, H is associated with multiple mental disorders, suggesting that H is transdimensionally associated with psychopathology. Here, we unify these results and demonstrate a pattern of decreased H with increased general psychopathology and attention-deficit/hyperactivity factor scores during a working memory task in 1,839 children. This pattern predicts current and future cognitive performance in children and some psychopathology in 703 adults. This pattern also defines psychological and functional axes associating psychopathology with an imbalance in resource allocation between fronto-parietal and sensory-motor regions, driven by reduced resource allocation to fronto-parietal regions. This suggests the hypothesis that impaired working memory function in psychopathology follows from a reduced cognitive resource pool and a reduction in resources allocated to the task at hand.
We study how the complexity of brain signals is associated with psychopathology. Using a measure of the fractalness of temporal brain dynamics, we find that psychopathology is associated with less fractal and less complex brain signals globally. In addition to this global pattern, we investigate spatial variations in the fractalness of brain signals. We find that disruptions in cognitive resources during a working memory task come from reductions in resources allocated to frontal regions alone. In addition, we find that these patterns of resource allocation are predictive of cognitive performance on multiple working memory tasks and a future working memory task. These findings suggest that future investigations of fractal brain dynamics in other contexts may help better understand the mechanisms behind psychopathology-associated cognitive impairment.
Handling Editor: Lucina Uddin