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Hallucinations in Parkinson's disease might happen as a results of shifts in the strengths of different brain networks

Visual hallucinations are common and distressing in Parkinson’s disease and are linked to poorer outcomes such as development of dementia or being admitted to a nursing home. However despite the impact they have on people with Parkinson’s and their families, we don’t really understand how they happen. There is new evidence that hallucinations might happen as a results of shifts in the strengths of different brain networks, but until now, it was not clear how that happened.

We looked at the wiring of the brains of people with Parkinson’s hallucinations and compared it to the wiring and connections of those with Parkinson’s but no hallucinations. We found that there was a sub-network of connections that was particularly affected in people with hallucinations, and that this network is especially influential for the whole of the brain, specifically affecting how the brain can switch between different states. We also looked at the genes that underlie this process and found that particular genes related to cell metabolism, and to movement of proteins within cells, are linked to higher vulnerability to hallucinations. Finally we showed that brain regions of the affected sub-network express fewer oligodendrocytes and higher amounts of neuronal cells.

Our findings provide insights to how changes in brain structure and wiring may result to the changes in brain function seen in Parkinson’s hallucinations. In addition, our findings suggest that expression of specific genes and cell types may make specific brain regions more vulnerable to degeneration in Parkinson’s, providing insights to potential therapeutic targets.