Imagine an undercover operative on a mission. At some point, she knows she'll need to call for backup - but pulling out a phone would be too risky, and there's no way to give a visible signal to her team.

Yet at the key moment, she can think "YES" - which could be interpreted as "yes, now is the time, go go go go go!" - and send that signal directly to the brain of a team member, who would see it as a flash and know that now is the moment to act.

That sort of direct communication from one brain to another sounds like telepathy, but technology that can read your brain's signals and send a simple signal (that means "yes" or "no" or whatever you choose) already exists - although our hypothetical portable version with hidden electrodes that could surreptitiously help covert agents communicate does not (yet!).

As we learn more about how our brains communicate - sending and interpreting electrical signals that mean "yes," "no," and more - the technology that now enables our basic brain-to-brain communication could allow us to do much more, potentially communicating full thoughts or even more.