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Simple vision tests can predict which people with Parkinson’s disease will develop cognitive impairment and possible dementia 18 months later, according to a new study by researchers at UCL.
The study, published in Movement disorders, adds to the evidence that vision changes precede cognitive decline that occurs in many, but not all, people with Parkinson’s disease.
In another new study published today in Communications biology, the same research team found that the structural and functional connections of brain regions become uncoupled throughout the brain in people with Parkinson’s disease, especially in people with vision problems.
Together, the two studies show how losses and changes in brain wiring underlie the cognitive impairment experienced by many people with Parkinson’s disease.
Lead author Dr Angeliki Zarkali (Center for Dementia Research, UCL Queen Square Institute of Neurology) said: “We have found that people with Parkinson’s disease who have visual problems are more likely to develop dementia, and this seems to be explained by underlying changes to their brain wiring.
“Vision tests could provide us with a window of opportunity to predict Parkinson’s dementia before it starts, which can help us find ways to stop cognitive decline before it’s too late. ”
For the Movement Disorders Paper, published earlier this month, researchers studied 77 people with Parkinson’s disease and found that simple vision tests predicted who would develop dementia after a year and a half.
Dementia is a common and debilitating aspect of Parkinson’s disease, estimated to affect about 50% of people within 10 years of being diagnosed with Parkinson’s disease.
These longitudinal results add weight to previous studies that were done at one point in time, which had suggested that performance in vision tests, involving commonly used eye charts and distorted images of cats and dogs, was linked to risk. cognitive decline.
The new study also found that those who developed Parkinson’s dementia had losses in brain wiring, including areas related to vision and memory. The researchers used newly developed methods to analyze finely detailed MRI scans, allowing them to detect damage to the brain’s white matter.
Researchers have identified white matter damage to some of the long-distance cables connecting the front and back of the brain, which helps the brain function as a cohesive whole network.
the Communications biology The study involved 88 people with Parkinson’s disease (33 of whom had visual dysfunction and were therefore deemed to be at high risk for dementia) and 30 healthy adults as a control group, whose brains were imaged. by MRI.
In the healthy brain, there is a correlation between the strength of the structural (physical) connections between two regions and the extent to which these two regions are functionally connected. This coupling is not uniform across the brain, as there is some degree of uncoupling in healthy brain, especially in areas involved in higher order processing, which could provide the flexibility to allow reasoning. abstract. Excessive decoupling seems to be linked to poor results.
Researchers found that people with Parkinson’s disease had a higher degree of decoupling throughout the brain. The areas at the back of the brain, and the less specialized areas, showed the most decoupling in patients with Parkinson’s disease.
Parkinson’s disease patients with visual dysfunction exhibited greater decoupling in some regions of the brain, but not all, particularly in regions related to temporal lobe memory.
The research team also found changes in the levels of certain neurotransmitters (chemical messengers) in people at risk for cognitive decline, suggesting that receptors for these transmitters could be potential targets for new drug treatments for the disease. Parkinson’s dementia. Notably, while dopamine is known to be involved in Parkinson’s disease, researchers found that other neurotransmitters – acetylcholine, serotonin, and norepinephrine – were particularly affected in people at risk for cognitive decline.
Dr Angeliki said: “The two articles together help us understand what goes on in the brains of people with Parkinson’s who experience cognitive decline, as it appears to be driven by a breakdown in the wiring that connects different regions. of the brain.”
Dr Rimona Weil (UCL Queen Square Institute of Neurology), lead author of the two papers, said: “Our results could be useful for clinical trials, showing that vision tests can help us identify who we should target for. trials of new drugs that could slow Parkinson’s disease. And finally, if effective treatments are found, these simple tests can help us identify who will benefit from which treatments. ”
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The researchers were supported by Alzheimer’s Research UK, Wellcome and the National Institute for Health Research UCLH Biomedical Research Center.
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