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155 results on '"Zarkali, Angeliki"'

3. The neural correlates of visual hallucinations in Parkinson's disease

Author

Zarkali, Angeliki

Abstract

Visual hallucinations are common in Parkinson's disease (PD) and linked to worse outcomes: increased mortality, higher carer burden, cognitive decline, and worse quality of life. Recent functional studies have aided our understanding, showing large-scale brain network imbalance in PD hallucinations. Imbalance of different influences on visual perception also occurs, with impaired accumulation of feedforward signals from the eyes and visual parts of the brain. Whether feedback signals from higher brain control centres are also affected is unknown and the mechanisms driving network imbalance in PD hallucinations remain unclear. In this thesis I will clarify the computational and structural changes underlying PD hallucinations and link these to functional abnormalities and regional changes at the cellular level. To achieve this, I will employ behavioural testing, diffusion weighted imaging, structural and functional MRI in PD patients with and without hallucinations. I will quantify the use of prior knowledge during a visual learning task and show that PD with hallucinations over-rely on feedback signals. I will examine underlying structural connectivity changes at baseline and longitudinally and will show that posterior thalamic connections are affected early, with frontal connections remaining relatively preserved. I will show that PD hallucinations are associated with a subnetwork of reduced structural connectivity strength, affecting areas crucial for switching the brain between functional states. I will assess the role of the thalamus as a potential driver of network-level changes and show preferential medial thalamus involvement. I will utilise data from the Allen Institute transcription atlas and show how differences in regional gene expression in health contributes to the selective vulnerability of specific white matter connections in PD hallucinations. These findings reveal the structural correlates of visual hallucinations in PD, link these to functional and behavioural changes and provide insights into the cellular mechanisms that drive regional vulnerability, ultimately leading to hallucinations.

Published
2021

10. Genetic topography and cortical cell loss in Huntington's disease link development and neurodegeneration

Author

Estevez-Fraga, Carlos, primary, Altmann, Andre, additional, Parker, Christopher S, additional, Scahill, Rachael I, additional, Costa, Beatrice, additional, Chen, Zhongbo, additional, Manzoni, Claudia, additional, Zarkali, Angeliki, additional, Durr, Alexandra, additional, Roos, Raymund A C, additional, Landwehrmeyer, Bernhard, additional, Leavitt, Blair R, additional, Rees, Geraint, additional, Tabrizi, Sarah J, additional, and McColgan, Peter, additional

Published
2023
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20. Neurofilament light-associated connectivity in young-adult Huntington’s disease is related to neuronal genes

Author

McColgan, Peter, primary, Gregory, Sarah, additional, Zeun, Paul, additional, Zarkali, Angeliki, additional, Johnson, Eileanoir B, additional, Parker, Christopher, additional, Fayer, Kate, additional, Lowe, Jessica, additional, Nair, Akshay, additional, Estevez-Fraga, Carlos, additional, Papoutsi, Marina, additional, Zhang, Hui, additional, Scahill, Rachael I, additional, Tabrizi, Sarah J, additional, and Rees, Geraint, additional

Published
2022
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22. Quantitative MRI maps of human neocortex explored using cell type-specific gene expression analysis

Author

Edwards, Luke J., McColgan, Peter, Helbling, Saskia, Zarkali, Angeliki, Vaculčiaková, Lenka, Pine, Kerrin J., Dick, Fred, Weiskopf, Nikolaus, Edwards, Luke J., McColgan, Peter, Helbling, Saskia, Zarkali, Angeliki, Vaculčiaková, Lenka, Pine, Kerrin J., Dick, Fred, and Weiskopf, Nikolaus

Abstract

Quantitative magnetic resonance imaging (qMRI) allows extraction of reproducible and robust parameter maps. However, the connection to underlying biological substrates remains murky, especially in the complex, densely packed cortex. We investigated associations in human neocortex between qMRI parameters and neocortical cell types by comparing the spatial distribution of the qMRI parameters longitudinal relaxation rate (equation ImEquation1), effective transverse relaxation rate (equation ImEquation2), and magnetization transfer saturation (MTsat) to gene expression from the Allen Human Brain Atlas, then combining this with lists of genes enriched in specific cell types found in the human brain. As qMRI parameters are magnetic field strength-dependent, the analysis was performed on MRI data at 3T and 7T. All qMRI parameters significantly covaried with genes enriched in GABA- and glutamatergic neurons, i.e. they were associated with cytoarchitecture. The qMRI parameters also significantly covaried with the distribution of genes enriched in astrocytes (equation ImEquation3 at 3T, equation ImEquation4 at 7T), endothelial cells (equation ImEquation5 and MTsat at 3T), microglia (equation ImEquation6 and MTsat at 3T, equation ImEquation7 at 7T), and oligodendrocytes and oligodendrocyte precursor cells (equation ImEquation8 at 7T). These results advance the potential use of qMRI parameters as biomarkers for specific cell types.

Published
2022

30. Fixel‐based analysis of the effect of amyloid beta on white matter tracts in neurologically normal 70 year olds

Author

Wagen, Aaron Z., primary, Zarkali, Angeliki, additional, Coath, William, additional, Buchanan, Sarah M., additional, Keuss, Sarah E., additional, Keshavan, Ashvini, additional, Lu, Kirsty, additional, James, Sarah‐Naomi, additional, Pavisic, Ivanna M., additional, Street, Rebecca E., additional, Parker, Thomas D., additional, Lane, Christopher A., additional, Murray‐Smith, Heidi, additional, Cash, David M., additional, Malone, Ian B., additional, Wong, Andrew, additional, Richards, Marcus, additional, Fox, Nick C., additional, Altmann, Andre, additional, Cole, James H., additional, Weil, Rimona S., additional, and Schott, Jonathan M., additional

Published
2021
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42. Longitudinal thalamic white and grey matter changes associated with visual hallucinations in Parkinson's disease.

Author

Zarkali, Angeliki, McColgan, Peter, Leyland, Louise Ann, Lees, Andrew John, and Weil, Rimona Sharon

Subjects
PARKINSON'S disease, WHITE matter (Nerve tissue), HALLUCINATIONS, CLINICAL neuropsychology, MENTAL representation, GRAY matter (Nerve tissue), BRAIN, RESEARCH, RESEARCH methodology, MAGNETIC resonance imaging, MEDICAL cooperation, EVALUATION research, THALAMUS, NEUROPSYCHOLOGICAL tests, COMPARATIVE studies, TELENCEPHALON
Abstract

Objective: Visual hallucinations are common in Parkinson's disease (PD) and associated with worse outcomes. Large-scale network imbalance is seen in PD-associated hallucinations, but mechanisms remain unclear. As the thalamus is critical in controlling cortical networks, structural thalamic changes could underlie network dysfunction in PD hallucinations.Methods: We used whole-brain fixel-based analysis and cortical thickness measures to examine longitudinal white and grey matter changes in 76 patients with PD (15 hallucinators, 61 non-hallucinators) and 26 controls at baseline, and after 18 months. We compared white matter and cortical thickness, adjusting for age, gender, time-between-scans and intracranial volume. To assess thalamic changes, we extracted volumes for 50 thalamic subnuclei (25 each hemisphere) and mean fibre cross-section (FC) for white matter tracts originating in each subnucleus and examined longitudinal change in PD-hallucinators versus non-hallucinators.Results: PD hallucinators showed white matter changes within the corpus callosum at baseline and extensive posterior tract involvement over time. Less extensive cortical thickness changes were only seen after follow-up. White matter connections from the right medial mediodorsal magnocellular thalamic nucleus showed reduced FC in PD hallucinators at baseline followed by volume reductions longitudinally. After follow-up, almost all thalamic subnuclei showed tract losses in PD hallucinators compared with non-hallucinators.Interpretation: PD hallucinators show white matter loss particularly in posterior connections and in thalamic nuclei, over time with relatively preserved cortical thickness. The right medial mediodorsal thalamic nucleus shows both connectivity and volume loss in PD hallucinations. Our findings provide mechanistic insights into the drivers of network imbalance in PD hallucinations and potential therapeutic targets. [ABSTRACT FROM AUTHOR]

Published
2022
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43. Flickering Stimuli Do Not Reliably Induce Visual Hallucinations in Parkinson's Disease

Author

Zarkali, Angeliki, Lees, Andrew J, and Weil, Rimona S

Subjects
genetic structures
Abstract

Visual hallucinations are a common and often distressing feature of Parkinson's disease; they are ephemeral and capricious, making them difficult to study but tend to be more prominent in dim illumination. Flickering stimuli can induce simple hallucinations even in healthy individuals. We tested a stroboscope and an equivalent full-screen flickering stimulus in 16 participants: 7 patients with Parkinson's and habitual visual hallucinations, 6 Parkinson's patients without hallucinations and 3 controls. Both flicker sources induced varied geometrical hallucinations in 4 participants (25%) and complex hallucinations in 1 but neither induced typical Parkinson's-associated hallucinations.

Published
2019

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