you see... there is no firewall to your brain... so they can hack it as they want...
The brain has some kind of immune system, though. People learn to ignore ads when reading web-pages, for example. And education can help too: critcal thinking helps resisting advertisment, and being aware of the ways salesmen try to trick you is also a good thing.
Right now, from what I've seen, all the experiments and developments about consumer behavior had underwhelming results. A simple look at the "targeted" ads on Facebook or Amazon recommendation shows that despite all the detailed information they've got about you, they mostly default to:
- things you've been looking at recently
- things that are very similar to them ("you like this book? You'll surely love this other edition of your book, or the sequel")
- ads related to very broad categories (single => dating, female => weight loss, etc.)
The problem isn't really what's happening now, it's what could be happening later, once these mechanisms start getting really efficient. Because then, all the data they're currently recording about you will suddenly become much more valuable and exploitable.