Your Fantastic Elastic Brain, by JoAnn Deak, Ph.D., illustrated by Sarah Ackerley, Little Pickle Press, 2010.
It is hard to imagine a Kindergarten kid getting excited about a picture book about brains, but my son was very excited about this book. He was so excited about this book that he picked it out when he earned a free book for reading 100 books in just over a month. (Yeah, my kid uses his brain.) :)
I didn't read all of the denser writing when I read the book to him tonight, but the lighter text and the illustrations were so engaging that I think my son chose well.