Somervail, Richard; (2021) Exploring the electrophysiological responses to sudden sensory events. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Living in rapidly changing and potentially dangerous environments has shaped animal nervous systems toward high sensitivity to sudden and intense sensory events - often signalling threats or affordances requiring swift motor reactions. Unsurprisingly, such events can elicit both rapid behavioural responses (e.g. the defensive eye-blink) and one of the largest electrocortical responses recordable from the scalp of several animals: the widespread Vertex Potential (VP). While generally assumed to reflect sensory-specific processing, growing evidence suggests that the VP instead largely reflects supramodal neural activity, sensitive to the behavioural-relevance of the eliciting stimulus. In this thesis, I investigate the relationship between sudden events and the brain responses and behaviours they elicit. In Chapters 1-3, I give a general introduction to the topic. In Chapter 4, I dissect the sensitivity of the VP to stimulus intensity - showing that its amplitude is sensitive only to the relative increase of intensity, and not the absolute intensity. In Chapter 5, I show that both increases and decreases of auditory and somatosensory stimulus intensity elicit the same supramodal VP, demonstrating that the VP is sensitive to any sufficiently abrupt sensory change, regardless of its direction or sensory modality. In Chapter 6, I observe strong correlations between the magnitudes of the VP and the eye-blink elicited by somatosensory stimuli (hand-blink reflex; HBR), demonstrating a tight relationship between cortical activity and behaviour elicited by sudden stimuli. In Chapter 7, I explore this relationship further, showing that the HBR is sensitive to high-level environmental dynamics. In Chapter 8, I propose an account of the underlying neural substrate of the VP, consistent with my results and the literature, which elucidates the relationship between the VP and behaviour. I also detail future experiments using fMRI and intracranial recordings to test this hypothesis, using the knowledge gained from this thesis.

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