Published before the end of the cold war, this story features a Russia at odds with the United States. It's written in the typical style of Asimov; the actual science of events is as carefully explained as events and people are in most other novels.
Dr. Morrison, a neurophysicist, is contacted by a Russian scientist involved in miniaturization. Quite quickly, he is kidnapped and brought to a secret Russian centre to help them. As the title would indicate, the eventual destination is a brain, but so's I don't blow the story, I won't say why. ;-)
Quite a lot of the book is spent inside the circulatory system of an actual person, and various things happen reminiscent of the comedy/action movie "Inner Space". The mechanisms for these events are explained in detail as usual, and I remember trying to recall details from my Biology classes. Not that I'm unsure that everything was exactly accurate, at least up to the date of publication.
This probably wouldn't be a very fascinating read to someone who wanted action and simplicity of the kind found in a generic Star Trek book, but the various twists and turns are interesting to someone who likes Isacc's genre of science fiction. I don't know if I recommend reading this book first (of his over 400)... Nightfall (also reviewed in my little list) might be a better book to start reading Isacc Asimov, although it's certainly a much easier read than his Foundation series, which I still intend to read when I finish my garage sale collection of paperbacks. Man is that ever a run on sentence, I'd say this particular review is done.