The MIT technology review discusses biological weapons Serguei Popov, a former Soviet bioweaponeer, claims that the soviets were successful making bioweapons that could alter behavior, and they investigated using pathogens to induce memory loss, depression, or fear. Plus they had bioweapons that could cause brain damage, paralysis, and nearly 100 percent mortality resulted. It is claimed that some of what the Soviet bioweaponeers did with difficulty and expense can now be done easily and cheaply. And all of what they accomplished can be duplicated with time and money.
How actually difficult is it? How much does new technology make it easier? New technology such as molecular nanotechnology will clearly provide a leap in the level of control over biology. Advances in biotech alone are changing the situation. It is clearly not getting harder or more expensive.
Fear, emotions and behavior have biological and chemical basis. Change and control those factors and you can effect behavior. Steroid rage is an unintended byproduct. LSD, heroin and other drugs effect behavior and perception.
If you were trying to cause a particular change, it seems reasonable that you could.