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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.   23 TS children aged 8-12 were compared to 67 controls on a battery of vibrotactile tasks \cite{26041822} with a subset also undergoing GABA-edited magnetic resonance spectroscopy. Lower right SM1 GABA concentration was associated with greater motor tic severity (r=-0.55). There were no significant differences between groups on reaction time and baseline amplitude discrimination threshold. Control children showed the expected increase in discrimination threshold after being exposed to a dyanamically increasing subthreshold stimulus while TS children did not. The authors suggest that this is related to abnormal GABAergic inhibition although it is not clear how much of this difference is due to the high proportion of TS subjects with ADHD.  | **Title** | **Comment** |  |:----------|:------------|  |