deletions | additions       diff --git a/Pathophysiology.md b/Pathophysiology.md  index 6ff4c5b..51d4231 100644  --- a/Pathophysiology.md  +++ b/Pathophysiology.md 
...
Researchers have used a variety of experimental paradigms to study motor response inhibition since tic expression seems related to motor inhibition difficulties. In healthy adults, performances on a stop-signal task and a continuous performance task were 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 availability in both the associative striatum and the sensory motor striatum. Neither D1- nor D2-type receptor availability was associated with performance on the continuous performance task, suggesting that the stop-signal and continuous performance tasks are associated with different neurochemical mechanisms related to motor response inhibition.   A review examined TS task-based fMRI studies in TS including studies of tic suppression, voluntary motor execution, voluntary motor inhibition, and tic severity \citep{26402403}. Free-ticcing conditions (four studies) most commonly activated the left cerebellum, right cingulum, left middle frontal gyrus, the Rolandic operculum, right pallidum, right SMA and thalamus. A summary of studies examiningstudies of  motor response inhibition studiesrevealed  that on NoGo trials TS subjects exhibited greater activation in the bilateral prefrontal cortex, thalamus and caudate. In contrast, on voluntary motor execution tasks greater activation in TS subjects was seen in the left prefrontal cortex, right cingulum, and the anterior portion of the SMA. Tic severity ratings were correlated with greater activation of the right dorsal premotor and the SMA. The premotor cortices of the medial wall (SMA/anterior cingulate cortex) were found to be involved across task types. The thalamus was involved in all types of studies except for self-produced movements. The authors also briefly summarize the the many issues related to neuroimaging studies such as the associated comorbidities, medication effects, the need for longitudinal studies, and the confounding effect of ticcing during scanning. A whole-brain analysis of cortical gray matter found reduced gray matter thickness in the insula and sensorimotor cortex for TS children and young adults compared to a matched control group \citep{26538289}. Premonitory Urge for Tics Scale scores were negatively correlated with grey matter thickness in these areas. These results demonstrate the value of examining neural substrates associated with premonitory urges separately from those associated with tic generation.