Mice turn into killers when brain circuit is triggered by laser!
In the 1962 Hollywood film, The Manchurian Candidate, Laurence Harvey plays the role of the son of a prominent right-wing political family, who becomes an unwitting assassin through brainwashing, in an international communist conspiracy. The film was released in the United States on October 24, 1962, at the height of the Cuban Missile Crisis. 
Almost a decade earlier, the now known project MKUltra begun by the CIA, sometimes referred to as the CIA's mind control program. MKUltra is the code name given to a program of experiments on human subjects, at times illegal, designed and undertaken by the United States Central Intelligence Agency. Experiments on humans were intended to identify and develop drugs and procedures to be used in interrogations and torture, in order to weaken the individual to force confessions through mind control. Organized through the Scientific Intelligence Division of the CIA, the project coordinated with the Special Operations Division of the U.S. Army's Chemical Corps. 
Although that some information regarding MKUltra was declassified since 2001, we can't know, of course, how far CIA or other agencies have gone with similar projects.
For example, although the CIA insists that MKUltra-type experiments have been abandoned, some CIA observers say there is little reason to believe it does not continue today under a different set of acronyms. Victor Marchetti, author and 14-year CIA veteran, stated in various interviews that the CIA routinely conducted disinformation campaigns and that CIA mind control research continued. 
Despite that MKUltra was created for the purpose of 'effective' interrogation and torture, the project has inspired many films and conspiracy theories that go beyond this function. As in the film described above, brainwashing and mind control could create a zombie-like assassin who could be programmed to kill specific targets, at the will of those who control him.
But now, a recent scientific discovery may trigger the appetite of some dark minds in the intelligence community, to create such a type of well-programmed assassins!
Researchers at Yale University have discovered that two sets of neurons in the mouse brain underpin the instinct to kill. One coordinates the pursuit of prey, while the other controls the neck and jaw muscles used for biting. Both are in the amygdala – the part of the brain involved in motivation, emotion and fear. Furthermore, by modifying these neurons so they could be activated by laser light, a technique called optogenetics, the team of scientists were able to switch these circuits on whenever they wanted. When the laser was off, the mice padded around their cages normally. But turning the laser on caused the mice to suddenly launch frenzied attacks on almost anything in their path: live crickets, fake insects or even sticks and bottle caps. After jumping on the “prey”, the mice grabbed it with their paws and repeatedly sunk in their teeth. 
Of course, the human brain is far more complicated and humans have evolved beyond their primitive instincts, in contrast with mice. Yet, under extreme conditions, human instincts are coming on surface. So far, from what we know, such CIA experiments have only led to multiple disorders for the people that have been used as experimental subjects.
Yet, as the progress towards the mapping of human brain will give increasingly better understanding of its functions, such discoveries as the one described, may revive the most advanced and nightmarish versions of evil projects like MKUltra.