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### Neuroimaging studies  The challenges of using neuroimaging techniques to study pediatric and clinical subjects are described in detail along with suggestions concerning various strategies that can be used to collect higher quality data \citep{26754461}. The profound effects on structural MRI findings of even very small head movements were identified in a well designed study \citep{25498430}. Neuroimaging scans were performed on 12 healthy adults while they were still or engaged in specific types of movement including nodding, head shaking or a movement each subject invented and then repeated during the scan run. Even during scans when subjects attempted to remain still, there was an average of 3 mm/min of accumulated motion measured using RMSpm (root mean square displacement per minute). Not surprisingly, displacement was significantly higher during the motion conditions and substantial impact was found on gray matter volume and thickness estimates. An average apparent volume loss of approximately 0.7% mm/min of subject motion was calculated. The greatest reductions in gray matter were found in the pre- and post-central cortex, in the temporal lobes and pole, and entorhinal and parahippocampal regions. Motion-associated increases in thickness were seen in some frontal regions and deep sulci such as the medial orbital frontal region. Significant effects due to motion were still present even after excluding scans that failed a rigorous quality control procedure. Recommendations included reducing head motion during scans as much as possible, controlling for motion in statistical analyses, and using correlational analyses to determine the associations between head motion and the predictors of interest. \citep{26654788} \citet{26654788}  described a method to limit the effects of movement artifacts by using a motion tracking system to provide prospective motion correction during scanning trials. Researchers have used a variety of experimental paradigms to study motor response inhibition since tic expression seems related to motor inhibition. In healthy adults, performance on a stop-signal task and a continuous performance task was examined using positron emission tomography to measure striatal D1- and D2-type receptor availability \citep{25878272}. Stop-signal reaction time was negatively correlated with both D1- and D2-type receptor activation in both the associative striatum and the sensory motor striatum. Neither D1- nor D2-type receptor activation was associated with Go reaction time or Stop signal reaction time on the continuous performance task, suggesting that these two tasks are associated with different neurochemical mechanisms related to motor response inhibition.