Multimodal investigations of self-referential cognition and underlying brain networks

Coulborn, Sean Ian ORCID: 0000-0001-8636-0864 (2022). Multimodal investigations of self-referential cognition and underlying brain networks. University of Birmingham. Ph.D.

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Abstract

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique which modulates the resting state potential of neurons and is becoming widely used in both the research and clinical settings. However, to date, little is understood about the effects of tDCS on brain activity/connectivity or how this translates into behavioural changes. Mind-wandering is an interesting phenomenon due to its self-generated nature, which by definition is produced spontaneously rather than influenced by external stimuli. Therefore, it is of interest to the scientific community to understand if mind-wandering can be modulated externally via tDCS. Previous research has reported that tDCS is able to modulate self-referential cognitive processes, such as mind-wandering, assessed via subjective self-reports. Furthermore, modulations to core regions of the DMN, an intrinsic brain network typically associated with self-referential cognition, have been observed in a small number of studies applying tDCS to the right inferior parietal cortex. However, the literature is highly inconsistent, with failed replications and large variations in methodological designs, leaving the efficacy of tDCS in modulating mind-wandering unclear. Given the known association between mind-wandering and activation of the DMN, in addition to the link between impaired DMN connectivity and numerous neuropsychological disorders, it is of interest to understand the ability to modulate this intrinsically directed process with an external medium, such as tDCS. This thesis investigates the effects of tDCS on mind-wandering and underlying intrinsic brain networks. In Chapter 3, stimulation of right inferior parietal lobule failed to modulate objective and subjective reports of mind-wandering and we provide support for this lack of an effect with Bayesian analysis. Chapter 4 replicates this lack of behavioural effect with the addition of brain imaging data displaying no effect of tDCS on underlying brain activation and connectivity. Chapter 5 evaluates the effect of tDCS over the left dorsolateral prefrontal cortex on mind-wandering and on brain activation (BOLD, dynamic functional and effective connectivity). No effect of stimulation was found across all measures, and we provide evidence to support this null effect. Together, the empirical chapters presented in this thesis provide consistent evidence for the lack of an effect of tDCS in modulating mind-wandering propensity and in modulating underlying brain activity and add to the body of literature highlighting the unreliability of earlier positive reports of its effect.
Due to COVID-19, the trajectory of the thesis was then adapted to allow the analysis of existing datasets. Chapter 6 evaluates disruptions in effective connectivity in prolonged disorder of consciousness (PDOC) patients between the DMN and anterior forebrain mesocircuit (AFM). PDOC patients displayed overall reduced coupling within the AFM which led to loss of inhibition from AFM to DMN, mostly driven by posterior areas. In turn, the DMN showed disruptions in self-inhibition of the midline regions. Our results provide partial support for the mesocircuit model of consciousness.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):