On brain images from particular MRI scans there are bright white patches that increase in older individuals. Interestingly, these same patches are often linked to dementia and cognitive decline. While there are different kinds of dementia – the most well-known and the one which affects the most people is Alzheimer’s disease – certain signs are invariably present. Prominent amongst these is a change to the blood flow in the vessels that provide oxygen and nutrients to the brain cells that are changed by the dementia. What then, causes these changes to the blood flow? We think it may have something to do with the way the heart is operating and are investigating this link in a cohort of half a million individuals of which ~ 80,000 have scans of both their brain and their heart. If we can establish a link between the heart and brain we would like to explore if there is something in the genes of these individuals that contributes to this.  As the genetic code for each of the individuals with heart and brain images has also been mapped, we can understand something about the genetic switches that causes these changes, and knowing these, may help in the search for potential treatments.