  Attention Deficit/Hyperactivity Disorder (ADHD) is one of the most common
neurodevelopmental disorders in children and is characterised by inattention,
impulsiveness and hyperactivity. While several studies have analysed the static
functional connectivity in the resting-state functional MRI (rs-fMRI) of ADHD
patients, detailed investigations are required to characterize the connectivity
dynamics in the brain. In an attempt to establish a link between attention
instability and the dynamic properties of Functional Connectivity (FC), we
investigated the differences in temporal variability of FC between 40 children
with ADHD and 40 Typically Developing (TD) children. Using a sliding-window
method to segment the rs-fMRI scans in time, we employed seed-to-voxel
correlation analysis for each window to obtain time-evolving seed connectivity
maps for seeds placed in the posterior cingulate cortex (PCC) and the medial
prefrontal cortex (mPFC). For each subject, the standard deviation of the voxel
connectivity time series was used as a measure of the temporal variability of
FC. Results showed that ADHD patients exhibited significantly higher
variability in dFC than TD children in the cingulo-temporal, cingulo-parietal,
fronto-temporal, and fronto-parietal networks ($p_{FWE} < 0.05$). Atypical
temporal variability was observed in the left and right temporal gyri, the
anterior cingulate cortex, and lateral regions of the right parietal cortex.
The observations are consistent with visual attention issues, executive control
deficit, and rightward parietal dysfunction reported in ADHD, respectively.
These results help in understanding the disorder with a fresh perspective
linking behavioural inattention with instability in FC in the brain.
