Epidemiology of cognitive dynamics in older adults

As people age, on average, their brains work less efficiently, especially their memory. With dementia, it is even worse. People with Alzheimer's disease, the most common cause of dementia, usually experience relentless decline. Their decline is both faster and more widespread than what normally happens with age. Even so, relentless decline is not what happens to everybody. Instead, even with dementia, some people decline much more slowly than do others, some stabilize and a few even improve. Stability and improvement are not studied very often, but that is what we aim to do. The reason to study more than decline is that we believe improvement is fundamental - and not just a fluke - and will tell us a lot about brain aging and dementia. We can do this using a type of mathematics known as dynamic systems modeling, which is well suited when things can get better or worse (e.g. weather forecasting). We have devised a dynamic systems model which has shown exceptional promise so far - so much so that leading dementia experts from the US and the UK are willing to share their very expensive data with us. One example of why we need this type of modeling is to understand how dementia prevention might work. It turns out that some interventions which might lower the risk of dementia also lower the risk of dying. This is a good thing, but it might also have a down side. Because the risk of developing dementia increases rapidly with age, if mortality is improved, some interventions could actually make dementia more common, by having more people live longer, to the ages at which dementia is very likely. (For example, past age 85, about one person in three has dementia.) So it is possible that unless a drug very markedly reduces the risk of dementia, the burden of dementia will increase. This is a tricky issue, which is why we need a sophisticated means of understanding all the ways in which prevention might change the burden of these progressive, damaging illnesses.