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Title: The role of the default mode network in contextual control
Author: Smith, Verity Holly Lim
ISNI:       0000 0004 8507 805X
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2020
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While extensive theories outline the importance of meaningful context in guiding goal directed behaviour, little evidence has emerged about the underlying cognitive mechanisms involved. This thesis aims to addresses this gap in the literature by integrating two commonly disparate topics in neuroscience: cognitive control and the default mode network. Chapter 2 considers why current studies of contextual control do not implicate DMN regions by comparing context-dependent decision making using rich, meaningful scenes, in comparison to arbitrary letter stimuli. DMN regions of the posterior cingulate cortex, parahippocampus and posterior inferior parietal cortex are found to show increased activity during decision making in the lifelike context only. Chapter 3 asks whether regions beyond the ‘task-positive’ multiple demand network are necessary for adequate performance in more lifelike naturalistic tasks. This neuropsychology experiment used behavioural data accumulated from brain lesioned patients across a series of naturalistic tasks and a standard IQ task. Naturalistic tasks were found to capture control processes beyond IQ and multiple demand network function, most likely depending on many processes and brain regions. Chapter 4 aims to understand to what extent the DMN contributes to non-spatial executive tasks. Replicating (Crittenden et al. 2015), DMN regions were found to represent the broader task domain and respond with greater activation to larger task switches and task restarts. A role for the DMN in transitions between distinct cognitive tasks is suggested. Chapter 5 assesses an alternative explanation for the switch effects of the previous chapter. The fMRI experiment presented in this chapter asks whether the activation of the DMN at cognitive transitions reflects changes in task rule retrieval difficulty instead of degree of task switch. To this end, this study directly manipulated the rule retrieval demands. Contrary to the retrieval account, increased retrieval demand led to reduced DMN activity, accompanied by increased activation in MD regions.
Supervisor: Duncan, John ; Mitchell, Daniel Sponsor: Medical Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: DMN ; default mode network ; cognitive control ; cognitive neuroscience ; fMRI