In order to perform a successful manipulation, the manipulating agent often has to be a close symbiont - in other words, a parasite.
To successfully manipulate its host, the nervous system is an attractive target. mind parasites. It is still possible to manipulate the host without invading their nervous system - and many parasites succeed by other techniques. They might synthesize hormones or neurotransmitters - or maybe make their hosts cough, sneeze or itch. However, these approaches don't really qualify as hijacking. One of the defining characteristic of a hijacking is that the hijacker directs many of the hijackee's actions.
The hijacking metaphor makes the most sense in the context of Richard Dawkins' characterization of the host's phenotype as being a vehicle. A parasitic hijacker may then hijack the host's vehicle and use it to its own ends.
Sometimes the victim's higher mental faculties are compromised during the hijacking - in which case the victim is often referred to as being a "zombie".
Hijacking parasites may be either organic or cultural. Memetic hijacking is a well-known phenomenon. Memetic hijacking illustrates the precise targeting that's available to cultural software. The host's motivational system can be reprogrammed to the point where they want nothing more that the success of the memeplex they are infected with. In some cases, the hosts are even sterilized by their memes - ensuring that resources that might otherwise be invested in childcare are directed into meme propagation.