deletions | additions       diff --git a/Pathophysiology.md b/Pathophysiology.md  index e256350..26d3ed6 100644  --- a/Pathophysiology.md  +++ b/Pathophysiology.md 
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### Neuroimaging and electrophysiology studies  An important (though frustrating) recent finding was that even very small head movements can cause artifactual findings in structural MRI \citep{25498430} . Neroimaging scans were performed on 12 healthy adults while they were still or engaged in specific types of movements including nodding, headshaking and a movement that they invented and then repeated during the scan run. Even during scans when subjects remained still, there was an average of 3 mm/s RMSpm (RMS displacement per minute), but it was significantly higher during the motion conditions. In general there was a 1-3% local volume loss for each 1 mm/s RMSpm increase. The greatest thickness reductions were found in the pre- and post-central cortex, in the temporal lobes and pole, and enthorhinal and parahippocampal regions. Increased thickness associated with motion was seen in regions associated with deep sulci such as the medial orbital frontal and lateral frontal areas. Recommendations were made to reduce head motion during scans as much as possible and then control for motion in the statistical analysis, along with using correlational analyses to determine the associations between head motion and the predictors of interest. A more recent article \citep{26654788} described the development of a system for motion tracking and prospective motion correction, and mentions similar systems that are available for other scanner platforms. The challenges using neuroimaging techniques to study pediatric and clinical subjects are described in detail along with various strategies that can be used to collect high-quality data \cite{26754461} . \cite{26754461}.  Many 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 striaum 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.  
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KEVIN--does this have adequate control for movement? Average maximum displacement for controls was .7 mm for controls and .9 mm for patients.  Magnetoencehalography was used with adults while they were performing a Go/No-Go task \cite{26649991}. TS subjects showed less beta suppression in the sensorimotor region and increased beta power in the parieto-occipital brain geions that were contralateral to the hand used for the task. The TS subjects had less beta suppression while preparing to move their fingers and increased beta activity on the Go trials. Beta power was higher in TS patients than controls in the parieto-occipital area.  | **Title** | **Comment** |