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Cognitive testing Our early work focused on the concept of ‘Mild Cognitive Impairment’ in Parkinson’s disease (PD-MCI); we were among the first internationally to do so. Mild cognitive impairment refers to cognitive ability that is below that expected for someone’s age when compared to others. We addressed potential criteria for the diagnosis of PD-MCI and our suggestions contributed to the International Movement Disorders Society’s Task Force criteria for this condition. Both our independent work and our contributions to a multinational consortium have confirmed that people who reach criteria for PD-MCI are at higher risk of progression to dementia. Dementia refers to the loss of everyday independent function and is associated with poor quality of life, substantial caregiver and financial burden, and early institutionalisation. The problem remains that the identification of PD-MCI does not specify an individual’s risk of dementia, as many do not progress to more advanced levels of cognitive decline. To improve this, our latest work has focused on identifying a selection of cognitive tests that best predict risk of progression to dementia. The value of this approach is that we can provide better clinical management and target potential treatments that are perhaps tailored for an individual’s current risk status. Brain imaging Brain imaging techniques provide us with powerful methods to describe the brain changes associated with cognitive impairment (Figure 1). In a 60-minute MRI scan, we acquire multiple types of MRI, giving information about different aspects of structural and functional brain health. These include white and grey matter structure, vascular integrity, chemical concentrations, iron accumulation, and functional status. A strength of the study is that we have repeated scans of the same individuals, so that we can track brain changes over time. We first characterised any brain changes associated with dementia. We identified loss of grey matter tissue, white matter damage, and reduction of blood flow to the brain in the Parkinson’s disease group with dementia relative to healthy controls and the group of Parkinson’s disease participants with normal cognition (Figure 2). These initial results suggested wide-ranging biological brain changes underlying cognitive impairment and the development of dementia in Parkinson’s disease. Furthermore, when tracking brain volume changes over time, the Parkinson’s disease group with normal cognition was indistinguishable from controls, but worsening cognitive impairments were associated with loss of brain tissue over time. A current challenge for us is that while the presence of PD-MCI increases the risk of developing dementia in general, we are still unable to precisely predict if and when any specific individual will develop dementia. In recent work generously funded by the Neurological Foundation, Figure 1. The brain imaging scanners and a few examples of scans. The left panel displays the MRI scanner with a structural T1-weighted MRI scan. The right panel shows the PET scanner with an amyloid PET scan. Figure 2. Horizontal brain slices highlighting differences between a group of Parkinson’s disease patients with dementia vs healthy controls. Blue- green represents significant loss of grey matter tissue (left panel) and reduced blood flow (middle panel). Red (right panel) indicates significant white matter damage along principal white matter tracts. Figure 3. Horizontal slices from amyloid PET scans. Blue indicates low levels of amyloid, while red indicates high levels. The left panel displays an amyloid negative scan showing low levels of cortical amyloid, while the right panel shows an amyloid positive scan, with high levels of amyloid throughout the brain. We identified no significant relationship between cognitive impairment and cerebral amyloid deposition. Headlines 17