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Title: Neural underpinnings of visual awareness investigated with transcranial magnetic stimulation


The studies included in this thesis employed Transcranial Magnetic Stimulation (TMS) to investigate brain areas assumed to be involved in the formation of visual awareness judgements. TMS is a non-invasive brain stimulation method that temporarily influences neuronal activity in the targeted brain area. The thesis includes three published scientific articles. The first, theoretical article, discusses the constraints of TMS-based inferences and offers recommendations on how to address these limitations, specifically in the context of repetitive TMS (rTMS). The second and third articles present within-participant design experimental studies where TMS was applied to different brain areas of healthy individuals to examine its impact on visual awareness judgements and metacognitive efficiency, that is the ability to accurately judge one’s own perception. Unlike neuroimaging methods, TMS can modulate neuronal activity, which makes it a valuable tool for drawing causal inferences. The first article discusses the use of TMS to deduce the causal relations between brain areas and their functions. It critically assesses the extent to which causal inferences can be derived from rTMS data. It emphasises that relying solely on rTMS data does not provide sufficient grounds for strong inferences about the direct causal properties of targeted brain areas. The article proposes s ; trategies for mitigating the limitations of rTMS, such as combining it with neuroimaging techniques and incorporating appropriate control conditions. It concludes that the strength of inferences drawn from rTMS studies largely depends on the experimental design, and rTMS may not always be suitable for answering questions related to causality. This article is intended for researchers aiming to design rTMS studies or interpret the results of rTMS studies causally. The second article investigates the involvement of the PFC in the processes underlying visual awareness. While some theories of consciousness highlight the importance of the PFC as the neural underpinning of visual awareness (e.g., higher-order theories of consciousness), a number of researchers argue that PFC activity is not essential. It has also been hypothesised that the PFC is closely associated with metacognition. Therefore, the first study investigated the role of the PFC in visual awareness judgements by comparing three different rTMS protocols applied to the left anterior medial prefrontal cortex (aMPFC), a brain area associated with metacognition, to induce plasticity-like effects. The study employed three distinct Theta Burst Stimulation (TBS) protocols, namely continuous TBS (cTBS), intermittent TBS (iTBS), and sham TBS. The TBS protocol was applied prior to the behavioural testing involving ; a computer-based procedure with visual identification task and visual awareness ratings. The results indicated that cTBS led to higher estimates of metacognitive efficiency than the sham TBS. This effect was associated with lower visual awareness ratings for incorrect responses. No significant differences were observed between the TBS conditions in terms of identification task performance or response times (RTs). The third article addresses the ongoing discussion in the consciousness research community concerning the impact of non-visual information on visual awareness judgements. It describes a study that examined whether single-pulse TMS (spTMS) applied to the primary motor cortex (M1) approximately half a second after a stimulus presentation can serve as a piece of non-visual evidence and consequently influence visual awareness ratings. The study also investigated whether spTMS-induced motor-evoked potential (MEP) amplitude can reflect the amount of accumulated perceptual evidence. The study hypothesised that applying spTMS to M1 results in higher visual awareness ratings compared to a control condition. It also assumed that MEPs amplitudes would correspond to the amount of accumulated evidence. The experimental setup consisted of spTMS with a computer-based procedure involving visual awareness ratings and a visual identification task. The results revealed ; that in congruent trials (where the response hand used in the identification task matched the one stimulated in the M1 condition), there were higher visual awareness ratings and longer identification task RTs in the M1 condition compared to the control condition. Additionally, longer RTs for visual awareness ratings were observed in the M1 condition compared to the control condition, regardless of congruence, potentially suggesting the incorporation of additional evidence into visual awareness judgements. No significant difference was observed between conditions in terms of metacognitive efficiency. Furthermore, the amplitudes of MEPs were associated with the visual awareness ratings and exhibited higher values in congruent trials, implying that MEP could serve as an indirect measure of accumulated evidence. Overall, the findings suggest that both the aMPFC and M1 can contribute to the formation of visual awareness judgements. However, it is crucial to recognise the limitations of the employed methods, especially TMS, and the intricate nature of the processes being studied.

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Level of degree:

2 - studia doktoranckie

Degree grantor:

Rada Dyscypliny Nauki medyczne


Wierzchoń, Michał ; Sandberg, Kristian

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pol; eng

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tylko w bibliotece

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Apr 15, 2024

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Apr 15, 2024

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UJCM293c5c548b02437ba8e01a3724d747a2 Apr 15, 2024


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