No one–to repeat, no one–understands how it happens. Every day, the minds of millions of high-functioning people slowly slip into another reality, one in which life events, loved one’s faces, children’s names and all the other memories that constitute a person’s identity have disappeared. Deep inside their brains, the slide begins decades before the symptoms of dementia manifest. By the time the car keys begin to go missing, it’s already far too late.

Currently, there are about 36 million people in the world suffering from dementia. By 2050, the population at risk for the disease is expected to hit two billion, causing what experts say will be an unprecedented health care crisis that could cost $1 trillion a year in the U.S. alone.