States of Mind: Understanding Ongoing Thought using Functional Magnetic Resonance Imaging

Ongoing thought makes up a large portion of daily life, and has been associated with varied neurocognitive processes and outcomes, including poor task performance and creativity, negative mood and improved well-being. This complexity arises due to the fact that (1) ongoing thought is multi-dimensional in nature (2) the context during which thought occurs has an important impact on its outcomes and (3) moments of stable, maintained cognition differ conceptually from transitions between states. These issues have led to disagreements in the literature about the role of certain systems during ongoing thought, particularly executive control and the default mode network. This thesis used a paradigm that measures ongoing thought using multi-dimensional experience sampling to capture state contents across two tasks that vary in their need for continuous monitoring. By placing ongoing thought within a multi-dimensional state
space, including time and context as independent variables, and using fMRI as a
covert measure of state and trait processing, this paradigm enabled a clearer
delineation of the neurocognitive systems engaged during ongoing thought. Results point to a role for the ventral attention network in monitoring external context to guide general state maintenance and a role for the dorsal attention network in transitioning between internal and external states. The default mode network was related to detailed thoughts and shown to be important for determining state contents through its interaction with perceptual regions. Executive resources were engaged to maintain both internal and external states, and fluid intelligence was associated with the ability to transition between these states in the most effective manner in line with the demands of the environment. Finally, state transitions were shown to involve wholebrain reorganisations along multiple dimensions that are rooted in the functional organisation of the brain at rest.