In a famous test, rats given a lever to activate their nucleus accumbens (the brain’s pleasure centre, responsible for dopamine production) pressed it continuously until they died of starvation or exhaustion. The same brain structure lights up when addicts score a fix.
Reports have emerged of young men dying following excessive bouts of video game playing: like rats, they forgot to eat, sleep or move. In one well-known case, a South Korean man died after 50 hours of non-stop gaming.
Studies suggest that brain activity seen in excessive internet users resembles that of drug addicts, with less grey matter volume in parts of the prefrontal cortex linked to willpower. But cause and effect is not clear: the difference could be a precondition for, rather than a result of, excessive internet use.