Children with ADHD exhibit lower fMRI spectral exponent than their typically developing counterparts

Complex interactions in nonlinear systems such as the human brain exhibit fractal processes which are outcomes of self-similar patterns over long time scales by a power law in the frequency domain. The spectral exponent (γ) of this power law can be observed as an estimator of relative health and disease especially in the case of 1/f power spectrum. The aim of this pilot study is to estimate the fractal behaviour (using spectral exponent) of resting state fMRI time series of children with ADHD when compared to age-matched and gender-matched typically developing children (TDC). We expect the spectral exponent of the children with ADHD to be significantly different from that of their typically developing counterparts. Our analysis shows that both the children with ADHD and TDC exhibited positive spectral exponent (γ) which implies that their fMRI time series depicts greater power at high frequencies. However, the children with ADHD exhibited significantly (p<0.05) lower spectral exponent (γ) than their typically developing counterparts in brain regions consistent with abnormalities in ADHD brain dynamics. Our results have shown that spectral exponent (γ) may be a useful tool in revealing abnormalities in ADHD brain dynamics.