衝動控制主要是將已準備執行的動作進行抑制的能力，當緊急情況發生時，此功能可使我們避免危險。在實驗研究中，停止訊號作業被最為廣泛地使用，並且發展出不同形式以因應不同的關於衝動控制的研究議題。先前研究指出，「前運動輔助區」(pre-supplementary motor area, pre-SMA)和「右側前額葉腦迴」(right inferior frontal gyrus, rIFG)皆與執行此應變能力有關，但對於這兩個腦區分別在衝動控制的角色卻未有一致的結論。本研究旨在探討忽略訊號對於停止訊號作業的影響，並利用跨顱磁刺激建立相關腦區在此神經機制下的因果關係。由於停止訊號出現時，具有突然出現且無法預測的特性，有些研究者認為，停止訊號並不單純是使受試者抑制動作，同時也包含了受試者對於此訊號的注意力攫取歷程。注意力搜尋作業發現rIFG與注意力攫取歷程有關。為了能將注意力攫取從停止訊號中分離出來，研究者在傳統停止訊號作業多增加一個「忽略」訊號，此訊息雖同樣具有不可預測性，但當受試者看到此信號時，被要求要持續地完成正在執行的動作。相關腦造影研究顯示，相對於忽略訊號，pre-SMA對於停止訊號的活化較大，支持pre-SMA確實與衝動控制歷程相關，然而忽略訊號的出現是否只有注意力攫取單一歷程卻受到挑戰。 實驗一目的為檢測停止訊號作業是否會受到忽略訊號影響，比較在傳統停止訊號作業與增加忽略訊號的選擇停止訊號作業間的表現，並對於受試者策略進行分析。結果顯示忽略訊號確實對選擇停止訊號作業有顯著的影響，並不單純是注意力攫取的效果。實驗二以跨顱磁刺激探究當忽略訊號出現時，pre-SMA與rIFG在當中的神經機制。首先，根據實驗一的結果，先將受試者對於忽略訊號的反應時間分為快與慢兩組。先前研究結果發現，反應時間慢可能代表衝動控制不完全，並提出pre-SMA與rIFG皆與其相關。實驗二結果發現，反應時間慢組，當刺激rIFG時能使其反應時間顯著變快，說明rIFG相對於pre-SMA對於衝動控制不完全有主要的影響。而在反應時間快組，則是發現在刺激pre-SMA時，反應時間會顯著變慢。雖然目前相關文獻對於反應時間快組並無大量的探討，且腦造影研究結果則是顯示rIFG在其中的活化，但實驗者推論，當忽略訊號出現而受試者能較快反應時，需要去抑制衝動控制的產生，而此部分則是由pre-SMA負責，因此在電刺激短暫干擾下反會使得反應時間增加。 pre-SMA與rIFG已被發現在功能與結構上是緊密連結的，本研究顯示在衝動控制的神經機制中，並對於不完全抑制的因果關係有初步了解，而未來研究期以在忽略訊號反應快者的神經機制做更深入地研究。;The presupplementary motor area (pre-SMA) and the right inferior frontal gyrus (rIFG) are critical for successful response inhibition. However, different conclusions regarding their roles have been made. Since stop signals usually appear abruptly and infrequently, it has been argued that attentional capture may be involved in the task. To dissociate inhibition and attentional capture, an “ignore” condition in a stimulus selective stop-signal task was introduced. Because the ignore signal shares all but one feature with the stop signal but does not require stopping, performance in the ignore conditions can be contrasted to that in the stop conditions. However, some argued that the role of the ignore signal might not be as straightforward as it seems. The current study aimed to examine how ignore trials may affect the inhibitory process and the causal relations of pre-SMA and rIFG in implementing such trials by using theta burst TMS (cTBS). The objective of Experiment 1 was to testify whether “ignore” trials affect performance by comparing participants’ performances in both simple and selective stop-signal tasks by strategy classifications. Results showed that ignore trials also influenced the stop process, indicating that ignore trials may not only represent attentional capture but also partial inhibition (i.e. response slowing). In Experiment 2, cTBS was applied over the pre-SMA and rIFG to further examine their roles in partial inhibition in participants whose ignore RTs were fast and those who were slow. Results showed a double dissociation between brain regions. cTBS over the rIFG showed a decrease in RT in the slow ignore RT group, indicating the involvement of rIFG in partial inhibition. On the other hand, cTBS over the pre-SMA showed an escalated ignore RT, suggesting that the ! iii pre-SMA might play a role in suppressing inhibitory function in order to respond fast in ignore trials.
