The defining character of tics is that they can be transiently suppressed by volitional effort of will, and at a behavioural level this has led to the concept that tics result from a failure of inhibition. However, this logic conflates the mechanism responsible for the production of tics with that used in suppressing them. Volitional inhibition of motor output could be increased to prevent the tic from reaching the threshold for expression, although this has been extensively investigated with conflicting results. Alternatively, automatic inhibition could prevent the initial excitation of the striatal tic focus-a hypothesis we have previously introduced. To reconcile these competing hypotheses, we examined different types of motor inhibition in a group of 19 patients with primary tic disorders and 15 healthy volunteers. We probed proactive and reactive inhibition using the conditional stop-signal task, and applied transcranial magnetic stimulation to the motor cortex, to assess movement preparation and execution. We assessed automatic motor inhibition with the masked priming task. We found that volitional movement preparation, execution and inhibition (proactive and reactive) were not impaired in tic disorders. We speculate that these mechanisms are recruited during volitional tic suppression, and that they prevent expression of the tic by inhibiting the nascent excitation released by the tic generator. In contrast, automatic inhibition was abnormal/impaired in patients with tic disorders. In the masked priming task, positive and negative compatibility effects were found for healthy controls, whereas patients with tics exhibited strong positive compatibility effects, but no negative compatibility effect indicative of impaired automatic inhibition. Patients also made more errors on the masked priming task than healthy control subjects and the types of errors were consistent with impaired automatic inhibition. Errors associated with impaired automatic inhibition were positively correlated with tic severity. We conclude that voluntary movement preparation/generation and volitional inhibition are normal in tic disorders, whereas automatic inhibition is impaired-a deficit that correlated with tic severity and thus may constitute a potential mechanism by which tics are generated.

中文翻译：

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在原发性抽动障碍中自动但完整的意志抑制受损。

抽动症的决定性特征是可以通过意志的自愿努力暂时抑制抽动症，而在行为层面上，这导致抽动症的概念是抑制失败。但是，这种逻辑使负责抽动的产生的机制与抑制抽动的机制混为一谈。可以增加对电机输出的自动抑制，以防止tic达到表达阈值，尽管对此进行了广泛研究，但结果相互矛盾。另外，自动抑制可以阻止纹状体聚焦的最初激发，这是我们先前引入的假设。为了调和这些相互矛盾的假设，我们在一组19名原发性抽动症患者和15名健康志愿者中检查了不同类型的运动抑制。我们使用条件性停止信号任务探究了主动和反应性抑制，并将经颅磁刺激应用于运动皮层，以评估运动的准备和执行。我们评估了带掩盖的启动任务的自动运动抑制。我们发现抽动障碍不会损害自愿运动的准备，执行和抑制（主动和反应）。我们推测这些机制是在自愿性抽动抑制过程中募集的，它们通过抑制抽动生成器释放的新生刺激来阻止抽动表达。相反，抽动障碍患者的自动抑制功能异常/受损。在蒙版的底涂任务中，发现对健康对照组有正面和负面的相容性影响，抽动患者则表现出很强的正相容性，但没有负相容性，这说明自动抑制作用减弱。与健康对照组相比，患者在掩盖的灌注任务上还犯了更多错误，并且错误的类型与自动抑制功能受损相一致。与自动抑制功能受损相关的错误与抽动严重程度呈正相关。我们得出的结论是，抽动障碍中的自愿运动准备/产生和自愿抑制是正常的，而自动抑制功能受损-与抽动严重度相关的缺陷，因此可能构成抽动产生的潜在机制。与健康对照组相比，患者在掩盖的灌注任务上还犯了更多错误，并且错误的类型与自动抑制功能受损相一致。与自动抑制功能受损相关的错误与抽动严重程度呈正相关。我们得出的结论是，抽动障碍中的自愿运动准备/产生和自愿抑制是正常的，而自动抑制功能受损-与抽动严重度相关的缺陷，因此可能构成抽动产生的潜在机制。与健康对照组相比，患者在掩盖的灌注任务上还犯了更多错误，并且错误的类型与自动抑制功能受损相一致。与自动抑制功能受损相关的错误与抽动严重程度呈正相关。我们得出的结论是，抽动障碍中的自愿运动准备/产生和自愿抑制是正常的，而自动抑制功能受损-与抽动严重度相关的缺陷，因此可能构成抽动产生的潜在机制。