Neuroscience of Charles Bonnet Syndrome

Plain-language summary

Charles Bonnet Syndrome (CBS) is a condition in which people experience complex visual hallucinations, such as 'Acrobats balancing on bicycles' or 'Spiders crossing meals'. The condition usually occurs in people who have significant vision loss due to eye disease. The aim of this project is to help understand how these hallucinations come about. In the healthy visual system, the eye provides input to a large area of the brain that performs the computations required to allow us to see the world. There are specialised brain regions responsible for processing of faces, objects, motion and colour. When the eye is no longer working, these parts of the brain lose their input and this may lead to abnormal activity. Not all people with eye disease and vision loss develop CBS, so the investigators will use magnetic resonance imaging (MRI) to compare the brains of people with and without the condition. In particular the investigators are interested in measuring the levels of chemicals in the visual areas of the brain to see whether they are disrupted in CBS, leading to the hallucinations. It is possible to measure how the different areas of the visual brain are connected together and see whether this is altered in CBS, perhaps with increases in the strength of connection between specialised areas. These measures will be related to questionnaires about hallucinations and vision. This will be done by comparing low vision who experience Charles Bonnet visual hallucinations compared to low vision patients who do not have hallucinations. Assessments will take place at the Wellcome Centre for Integrative Imaging (WIN) based at the John Radcliffe Hospital. The study will provide insight into the role of the brain in generating CBS hallucinations, helping us to design a larger study and eventually to test whether there are interventions to help improve the condition.

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