Ignoring the ethical and legal problems with torture, the main problem that is not usually portrayed in films is that people say whatever the interrogator wants to stop the pain.

interrogator> We have been torturing you for 10 hours. If you spell "John" we will stop torturing you and torture John instead.

interrogated> [The pain is too much. We have a deal. Sorry John.] JOHN

A better interrogator can be more subtle, like

interrogator> We have some evidence [1] that John is the one that put the bomb, and that you are innocent, but my boss is not sure. If you confirm this info we will send you immediately to your cell.

[1] It's a lie! Also, John is innocent in case you are wondering.

Oh that's interesting, make them think the thoughts at least for extraction. This first version of the tech requires the user to mentally imagine moving muscles to trace letters so yeah it's not likely to be an option... yet.

I wonder what happens to these BCI results when the user is on psychedelics a la MK Ultra

EDIT: Wait your point was slightly different then I first read but that makes perfect sense!