Every year the US Army holds an annual conference called the "Mad Scientist Future Technology Seminar" that considers blue sky ideas for the future of warfare.
Wired's Danger Room discusses the conference and links to an unclassified pdf summary of the meeting which contains this interesting paragraph about 'neuro-cognitive warfare':
In the far term, beyond 2030, developments in neuro-cognitive warfare could have significant impacts. Neuro-cognitive warfare is the mashing of electromagnetic, infrasonic, and light technologies to target human neural and physiological systems. Weaponized capabilities at the tactical level will be focused on degrading the cognitive, physiological, and behavioral characteristics of Soldiers. Its small size and localized effects will make it ideal for employment in urban areas. Such technology could be employed through online immersive environments such as 2d Life or other electronic mediums to surreptitiously impact behavior without the knowledge of the target.
I presume '2d Life' refers to Second Life, but I could be wrong.
The first part is discussing the conventional development of warfare technology designed to target the nervous system, which is a long-established military tradition that has included weapons such as the rock, the poison-tipped arrow, the nerve gas shell and a new generation of hush-hush electromagnetic weapons.
The second part is a little more interesting, however, it implies that a certain form of stimulation embeddable in a popular game or internet service (I think they're too shy too to say porn) might reduce cognitive performance by only a fraction, but when considered over a whole army, it could make a difference to the overall fighting force.
The scenario is a little bit science fiction (Snow Crash anyone?) but is an intriguing possibility given that only a slight change would be needed in an individual to justify its effect if it could be distributed over a wide enough population.
For example, many priming studies have shown it is possible to influence behaviour just by exposing people to certain concepts.
In one of my favourite studies, exposing people to ideas about elderly people slowed their walking speed, while a more recent experiment found this effect could change action sequences as well.