This interesting TED talk is a presentation (18' video) about controlling behaviour of flies using both DNA modifications and light. The experiment involves flies genetically modified to develop light triggers on certain neurons, and then using light beams to control them.

Now I'll do some speculation, joining a couple of dots. I remember reading about how a lab-engineered virus (maybe H1N1) could be a mean to spread some DNA into every human infected. What if that DNA is designed to cause neurons in some parts of our brain to develop triggers sensitive to external stimulus like electromagnetic waves (light, radio, etc), as shown in the video? That way we could be quite succesfully controlled using satellites. If these modified neurons are carefully placed they could fire emotional reactions of any kind, and the control could be targeted to a single individual, or to a wide area like a whole city.