surgically an electrode is implanted in the pleasure centre of the limbic system in monkeys brain. it is connected to a lever which the monkey can manipulate to generate pleasureable impulses. the monkey is then caged n observed.
initially, the monkey experiments with the lever tikk eventually, he discovers how to please himself.
as he learns, he begins to manipulate the lever more often, to get more pleasure.
once he's familiar with the technique, the lever takes over his activities.. and he gives up food, water and sleep, continually pressin the lever.. even if it ultimately leads to his death.
in common parlance, we call this phenomenon addiction