How healthy is your brain? We now know how to find out

How healthy is your brain? In our efforts to keep our brains healthy, how do we know what is working? It shouldn't have been difficult: 72 x 72. From the back seat, my daughter, newly confident in mental maths, wanted to check her answer. Whether it was because it was the end of the day, I was trying to park or something else, I stalled, cognitively speaking. Lately, though, I have had the sense that my brain isn't firing on all cylinders.