Abstract
Charles Bonnet syndrome (CBS) is a rare condition characterized by visual impairment associated with complex visual hallucinations in elderly people. Although studies suggested that visual hallucinations may be caused by brain damage in the visual system in CBS patients, alterations in specific brain regions in the occipital cortex have not been studied. Functional connectivity during resting-state functional magnetic resonance imaging (rs-fMRI; without hallucinations) in CBS patients, has never been explored. We aimed to investigate brain structural and functional changes in a patient with CBS, as compared with late blind (LB) and normally sighted subjects. We employed voxel-based morphometry and cortical thickness analyses to investigate alterations in grey matter characteristics, and rs-fMRI to study changes in functional brain connectivity. Decreased grey matter volume was observed in the middle occipital gyrus and in the cuneus in the CBS patient, and in the middle occipital gyrus and in the lingual gyrus within LB subjects, compared to their respective control groups. Reductions in cortical thickness in associative and multimodal cortices were observed in the CBS patient when comparing with LB subjects. The precuneus exhibited increased functional connectivity with the secondary visual cortex in the CBS patient compared to the controls. In contrast, LB patients showed decreased functional connectivity compared to sighted controls between the DMN and the temporo-occipital fusiform gyrus, a region known to support hallucinations. Our findings suggest a reorganization of the functional connectivity between regions involved in self-awareness and in visual and salience processing in CBS that may contribute to the appearance of visual hallucinations.
Highlights
Charles Bonnet syndrome (CBS) is a rare syndrome characterized by complex and recurrent visual hallucinations in people without psychological disorder
We used voxel-based morphometry (VBM) to study differences in grey matter density, and cortical thickness analysis to investigate structural cortical rearrangement in CBS (given that the present patient suffers from a degenerative eye disease, we focused on the lateral geniculate nucleus (LGN) from the visual pathways)
In order to disentangle brain modifications due to the late visual loss from those underpinning complex visual hallucinations typical of CBS, we included a group of late blind (LB) subjects without any visual hallucinations
Summary
Charles Bonnet syndrome (CBS) is a rare syndrome characterized by complex and recurrent visual hallucinations in people without psychological disorder. This syndrome typically occurs in people who have a visual deficit, generally resulting from macular degeneration, optic neuritis, cataracts, retinitis pigmentosa, glaucoma or diabetic retinopathy [1]. Previous magnetic resonance imaging (MRI) studies have provided diverging results about the presence of structural brain alterations in CBS patients. Functional connectivity during resting state functional magnetic resonance imaging (rs-fMRI), i.e. without active hallucinations in CBS patients, has never been reported. Resting state may offer an ideal approach for providing novel insights into the functional pathways that allow the emergence of visual hallucinations
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