The Woven Sensorium : An Examination of Aberrant Cross-Sensory Experiences in Hyperexcitable Cortex

Farrelly, Haydn and Braithwaite, Jason J and Nuttall, Helen (2026) The Woven Sensorium : An Examination of Aberrant Cross-Sensory Experiences in Hyperexcitable Cortex. PhD thesis, Lancaster University.

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Abstract

A heightened predisposition to anomalous perceptual experiences is associated with aberrant patterns of neuronal activity in the cerebral cortex, referred to as cortical hyperexcitability. Increasingly evidence across clinical and neurotypical populations suggests that, where an individual experiences anomalous perceptual experiences, these predominantly occur across multiple sensory domains, and are not confined to a single modality. This has led to the suggestion that cortical hyperexcitability may be a domain-general property of predisposition to aberrant perceptual experiences. The present thesis examined this hypothesis in relation to both state-based and trait-based factors of cortical hyperexcitability in neurotypical individuals. The underlying motivation was that high gain states associated with cortical hyperexcitability may lead to a misattribution of neuronal filtering, creating susceptibility to sensory ‘cross-talk’ from one domain into another. In Chapter 2 an Exploratory Factor Analysis with Parallel Analysis was conducted to form a trait-based measure of cortical hyperexcitability across auditory and visual domains - the Audiovisual Aberration Scale (AVAS). In Chapter 3 a multisensory adaptation of the visual Pattern Glare test was used to demonstrate a cross-sensory enhancement effect of aberrant visual experiences. Here experiences of Pattern Glare (visual irritation and distortions) associated with the presentation of irritating visual gratings were enhanced by the concurrent presentation of an irritating auditory tone. In Chapter 4 a rhythmic contrast reversal was introduced to Pattern Glare gratings, somewhat similar to photic visual flicker, to elicit visual hallucinations alongside distortions and irritation. Here hallucinations and irritation, but not distortions, demonstrated a similar cross-sensory enhancement effect with concurrent auditory stimulation. Crucially, across both Chapters 3 and 4, predisposition to cross-sensory enhancement was found to vary in sympathy with both state-based and trait-based indications of cortical hyperexcitability. Finally, in Chapter 5 a decoupling effect (i.e. abolition of cross-sensory enhancement) was demonstrated by applying intermittent theta burst stimulation (iTBS) to the left Temporoparietal Junction (TPJ) prior to completing the multisensory Pattern Glare test introduced in Chapter 3. This decoupling effect was also found to vary in sympathy with both state-based and trait-based indications of cortical hyperexcitability. Together these findings have demonstrated that cortical hyperexcitability may well work beyond the confines of a single sensory domain in modulating predisposition to anomalous perceptual experiences. A hodotopic interpretation of these results was presented, suggesting that localised gain processes at the TPJ may mediate state-based cortical hyperexcitability, and diffuse gain processes may mediate trait-based cortical hyperexcitability.