I'm close to tears behind my thin cover of sandbags as 20 screaming, masked men run towards me at full speed, strapped into suicide bomb vests and clutching rifles. For every one I manage to shoot dead, three new assailants pop up from nowhere. I'm clearly not shooting fast enough, and panic and incompetence are making me continually jam my rifle.
My salvation lies in the fact that my attackers are only a video, projected on screens to the front and sides. It's the very simulation that trains US troops to take their first steps with a rifle, and everything about it has been engineered to feel like an overpowering assault. But I am failing miserably. In fact, I'm so demoralised that I'm tempted to put down the rifle and leave.
Then they put the electrodes on me.
I am in a lab in Carlsbad, California, in pursuit of an elusive mental state known as "flow" - that feeling of effortless concentration that characterises outstanding performance in all kinds of skills.
Flow has been maddeningly difficult to pin down, let alone harness, but a wealth of new technologies could soon allow us all to conjure up this state. The plan is to provide a short cut to virtuosity, slashing the amount of time it takes to master a new skill - be it tennis, playing the piano or marksmanship.
That will be welcome news to anyone embarking on the tortuous road to expertise. According to pioneering research by Anders Ericsson at Florida State University in Tallahassee, it normally takes 10,000 hours of practice to become expert in any discipline. Over that time, your brain knits together a wealth of new circuits that eventually allow you to execute the skill automatically, without consciously considering each action. Think of the way tennis champion Roger Federer, after years of training, can gracefully combine a complicated series of actions - keeping one eye on the ball and the other on his opponent, while he lines up his shot and then despatches a crippling backhand - all in one stunningly choreographed second.
Flow typically accompanies these actions. It involves a Zen-like feeling of intense concentration, with time seeming to stop as you focus completely on the activity in hand. The experience crops up repeatedly when experts describe what it feels like to be at the top of their game, and with years of practice it becomes second nature to enter that state. Yet you don't have to be a pro to experience it - some people report the same ability to focus at a far earlier stage in their training, suggesting they are more naturally predisposed to the flow state than others. This effortless concentration should speed up progress, while the joyful feelings that come with the flow state should help take the sting out of further practice, setting such people up for future success, says Mihaly Csikszentmihalyi at Claremont Graduate University in California. Conversely, his research into the flow state in children showed that, as he puts it, "young people who didn't enjoy the pursuit of the subject they were gifted in, whether it was mathematics or music, stopped developing their skills and reverted to mediocrity."