This is a very cool (if disturbing) field of research. There's a lot of recent stuff coming out that shows this sort of thing is far more common than we used to think. In many cases, the various 'controllers' will use hormones to trigger behaviors in the host, but there are other ways to cause the host to do what you want. The Emerald Cockroach Wasp, for instance, isn't a parasite, and it achieves its goal by a very specific injection of certain chemicals into very small regions of the cockroaches body and brain that turn the roach into a 'zombie'. http://en.wikipedia.org/wiki/Emerald_coc...

Other direct controllers are more what you're thinking of, with ants, spiders and other arthropods generally serving as unwitting hosts for certain organisms:

http://www.ted.com/talks/ed_yong_suicida...

http://io9.com/5918948/fungal-infection-...

http://phenomena.nationalgeographic.com/...

With more and more information turning up about how our internal and external microbial community affects us, it wouldn't surprise me to learn that a lot of our behaviors may be modified by certain bacteria or even viruses.

mind controlling parasite is a fact, mostly happens to insects by parasitic worms, parasitic wasps, or even parasitic fungus. but how do they do it? i mean, the host has a brain and probably brain cells, but how do they know how to control and tinker with it?

and if a human has developed a parasite within his brain, can he become a madman, or even brain-controlled like a zombie?