The apparently dead subject was shown images of different human faces, which displayed a variety of emotions. A brain scan of a type called fMRI showed brain activity when some of the images were changed. It appeared that the brain, even after death, was perceiving visual images and thinking about the emotional meaning of them in some way.
The Lost Symbol is written in a compelling style, unless you stop to think about it for more than a second or two. If you’re going to read this book, do it fast, and just forget about reality.