Viewers literally peer into Alda’s head with a variety of high-tech imaging techniques, looking for his human spark.

In the third program, viewers literally peer into Alda's head with a variety of high-tech imaging techniques, looking for his human spark. The unique circuitry that provides us with our most prized ability, language, is closely tied to another unique human skill, our ability to make and use complex tools. In his own brain, Alda finds the site of his ability to figure out what others are thinking. And in perhaps the biggest surprise, he discovers that the essential human spark, our ability to build alternative worlds in our heads - to imagine - lies in a brain region closely related to that used when thinking about others' minds - and that fires most fiercely when we are doing nothing at all.