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Domain-general control mechanisms underlying stopping of thought and action



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Sankarasubramanian, Subbulakshmi 


The stopping of pre-potent responses that are incompatible with current goals is termed as response inhibition. The need to stop arises in a broad range of cognitive contexts and comes in handy regardless of whether you’re crossing the road, or trying to stop the retrieval of an unwanted memory from coming into awareness. Are all these forms of stopping the same? Are there common brain regions and mechanisms, which mediate response inhibition regardless of whether one is stopping an action or a thought? In this thesis, we address these questions, and probe the mechanisms mediating stopping. Response inhibition is thought to be achieved either proactively, by preventing the unwanted response, or reactively, by cancelling the already initiated response. Previous studies have shown that a)action stopping is mediated via distinct fronto-sub-cortical interactions that achieve proactive and reactive control, b) stopping actions and thoughts engages co-localized activity c) the right dorsolateral prefrontal cortex(DLPFC) and the right ventrolateral prefrontal cortex(VLPFC), dynamically inhibit different target regions depending on whether memory control or motor control is required d) regions involved in memory and emotion are inhibited in parallel by stopping mechanisms. Based on these findings, we posit that domain general inhibitory control is mediated by fronto-sub-cortical loops that support distinct proactive and reactive control mechanisms. Furthermore, we also posit that these control mechanisms may also play a role in other cognitive domains which have been previously shown to deploy inhibition, like attention. We tested our hypothesis of domain general control using a variety of tasks and techniques. Chapter 2 reports a behavioural experiment that investigates if memory control and attentional control are related, by having the same set of participants perform a memory control task (the Think No-Think task [TNT]) and a visual selective attention task (the Theory of Visual Attention task [TVA]). This findings of this study suggest a link between the mechanisms engaged by two tasks; people who are better at ignoring distractors in the visual attention task also showed greater mnemonic and affective inhibition in the memory control task. Chapters 3-5 then turn to the relationship between mnemonic and motoric stopping and whether common proactive and reactive control mechanisms are involved in each. Chapter 3 investigates fronto-striatal mechanisms of proactive control underlying both motor and memory control. Its findings reveal that the putamen is involved in both domains of stopping, and provide evidence for the causal interaction of the right DLPFC and VLPFC with this structure during both action and thought stopping. Chapter 4 is concerned with reactive control mechanisms, and it involves analysis of pooled data from 10 previous imaging studies involving memory control. The sub-thalamic nucleus (STN) is a part of the basal ganglia nuclei, and an important region implicated in motor stopping; its involvement in memory stopping is presented for the first time in Chapter 4. Chapter 5 investigates the causal necessity of the right DLPFC in inhibitory control of thought, action and emotion, by using transcranial magnetic stimulation (TMS) to temporarily produce ‘virtual lesions’ in the DLPFC and study the impact of this disruption on people’s ability to suppress their memories, regulate associated emotions or stop their motor actions. Chapter 5 provides evidence for the causal necessity of the right DLPFC, as people who received disruptive TMS to their right DLPFC were subsequently worse at forgetting of unwanted memories, controlling intrusive thoughts, regulating affect and stopping their motor actions, compared to participants who received sham stimulation instead. Taken together the findings in this thesis provide direct evidence to show that there are domain general fronto-subcortical mechanisms underlying stopping of prepotent responses, and that these responses are either proactively or reactively mediated by frontal structures like the right DLPFC, and subcortical structures like the putamen and the STN.





Anderson, Michael C


Memory, Inhibitory control, Memory Control, Motor Control


Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge
Mind Science Foundation, Cambridge International Trust