The neurocognitive factors underlying anomalous experience in the non-clinical population

Marchant, Rachel Ellen (2021). The neurocognitive factors underlying anomalous experience in the non-clinical population. University of Birmingham. Ph.D.

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Anomalous experiences (such as hallucinations) are known to occur in healthy, non-clinical groups. Despite this, the neurocognitive mechanisms underlying such experiences in these groups has received little attention. This thesis therefore aimed to explore the relationships between anomalous experience and one candidate neurocognitive mechanism, cortical hyperexcitability, in non-clinical samples.

Chapters 2 and 3 explored the contribution of visual cortical excitability to anomalous experiences in multiple modalities, by investigating the relationship between trait (questionnaire) and state (pattern glare) anomalous experiences under transcranial direct current stimulation (tDCS) of different areas of extrastriate cortex; Brodmann’s areas 5 and 7, and 17-19 (targeted with electrode sites Pz and POz respectively). These chapters evidenced differential relationships between visual trait and state measures. Chapter 2 revealed a trait-state relationship a relationship that was influenced by anodal tDCS brain stimulation, but only in those predisposed to pattern glare (indicating cortical hyperexcitability). Chapters 2 and 3 evidenced significant interactions between state experiences of pattern glare and tDCS condition, suggesting that these anomalous experiences vary depending on baseline excitability.

Chapter 4 explored whether the trait-state relationships observed within the visual modality in the previous chapters could be extended to auditory cortex. Trait and state anomalous experiences were again measured using questionnaires and pattern glare respectively. EEG-based sensory gating was used to index state auditory cortex inhibition. Chapter 4 tentatively suggested a cross modal relationship, with greater trait predisposition to anomalous visual experiences associated with greater suppression of the auditory P2 component. Greater P2 suppression may lead to source labelling errors and so perceptual distortions.

Overall, this thesis indicates intriguing subtleties in the relationships between trait and state measures of anomalous experience and cortical excitability, that are also modality-dependent.

Type of Work: Thesis (Doctorates > Ph.D.)
Award Type: Doctorates > Ph.D.
Licence: Creative Commons: Attribution-Noncommercial-No Derivative Works 4.0
College/Faculty: Colleges (2008 onwards) > College of Life & Environmental Sciences
School or Department: School of Psychology
Funders: Economic and Social Research Council
Subjects: Q Science > Q Science (General)


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