A multimodal investigation into the relationship between ongoing brain state dynamics and visual response variability

Ingram, Brandon Thomas ORCID: 0000-0002-8377-9245 (2024). A multimodal investigation into the relationship between ongoing brain state dynamics and visual response variability. University of Birmingham. Ph.D.

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Abstract

The human visual system exhibits a large amount of variability in visual responses, even when presented with identical stimuli, yet the mechanisms behind this variability remain poorly understood. This thesis utilised simultaneous EEG-fMRI and Hidden Markov Modelling to investigate ongoing brain state dynamics and evaluate their impact on visual responses. The first results chapter (Chapter 3) investigates the ability of Hidden Markov modelling to identify differences in BOLD and alpha brain state dynamics between eyes open and eyes closed rest. The results showed that each rest condition shows significantly different BOLD and alpha brain state dynamics, with the open condition being associated with attention-based network states and a reduction in alpha power. Hidden Markov modelling was then applied to a visual dataset, in which participants viewed left visual field checkerboards passively (i.e. no task) and actively (i.e. identifying target stimuli). A total of three separate models were trained: a whole-brain BOLD state model (Chapter 4), an alpha state model (Chapter 5) and a thalamus BOLD state model (Chapter Chapter 6). The results of these models demonstrated that the HMM state active at baseline had a significant impact on the subsequently evoked BOLD, VEP and alpha event-related de/synchronisation responses. Thus, the ongoing brain state dynamics, defined by BOLD measures and electrophysiological, explain a significant proportion of the variability in visual responses, highlighting the importance of the baseline. Overall, this thesis demonstrates that ongoing brain state dynamics interact with visual responses, resulting in the observed variability, highlighting the importance of accounting for the baseline in visual research and neuroimaging.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):