Thirteen teenage boys in an Aussie sleep study played Call of Duty 4: Modern Warfare for 50 minutes sat in bed (not the same one) under the covers with electrodes attached and lights dimmed.

Most fell asleep within seven-and-a-half minutes of stopping the game. They took four minutes to drop off after watching the visual equivalent of Proza March of the Penguins for 50 minutes.

"We purposefully chose a very tranquil film to contrast against the very stimulating effect of playing a violent video game in the hope of producing the greatest effect on sleep," lead researcher Michael Gradisar of Flinders University in Adelaide, said. "We were surprised that playing the violent video game did not lead to a much longer time taken to fall asleep."

None of the 13 participants - all "evening types" had sleep problems and, as Gradisar acknowledges, few boy would limit their playing time to just 50 minutes a night.

He also thinks that calorie-burning games such as "Guitar Hero" or Nintendo Wii would be sure to increase alertness - but, really, what teenage boy will play on the Wii when he should be in bed, when he could be playing adult-rated computer games.

Of course playing such games could in time turn the boy into a homicidal man. But the Flinders research confirms some thing we all knew already: teenage lads are spectacularly insensitive.