Oscillatory mechanisms of goal-directed control: a central role of frontoparietal theta

Top-down control over thoughts and behaviours is a hallmark of flexible, goal-directed cognition. This cognitive control is imperative for everyday functioning, allowing task-appropriate maintenance and shifting of priorities in line with needs. Cognitive control is known to rely on extensive frontoparietal networks, however, there is limited understanding of the functional mechanisms that facilitate cognitive control. That is, we know what parts of the cortex are involved in goal-directed behaviour but not necessarily how flexible, goal-appropriate communication between these regions is achieved. As such, this thesis aimed to characterise the ‘functional architecture’ of cognitive control. In this thesis, low-frequency theta (4-7 Hz) oscillations were targeted as a potential neural mechanism by which goal-appropriate information could be transmitted within frontoparietal networks. To determine the role of theta in frontoparietal network functioning, cued-trials task switching paradigms were utilised with simultaneous electroencephalography (EEG) recorded. Cued task switching allowed dissection of the temporal dynamics of cognitive control (i.e., proactive vs. reactive control processes), while EEG provided high temporal fidelity of theta activity associated with cognitive control. This thesis finds theta oscillations were critical to cognitive control at multiple levels. Firstly, theta oscillations were sensitive to temporal aspects of cognitive control. Both proactive and reactive cognitive control modes were associated with frontoparietal theta activity and theta oscillations during proactive control were predictive of behavioural performance. Secondly, theta oscillations were sensitive to differences in task context. Contextual demands during task switching and additional control paradigms (oddball, go/nogo) were quantified using information theory. Across task contexts, theta oscillations were present with distinct spatiotemporal signatures. Together, theta oscillations were found to be sensitive to both temporal and task contexts. As such, this thesis proposes that theta oscillations may represent a common, functional mechanism facilitating goal-relevant information propagation in frontoparietal networks, operating over multiple timescales and task demands.