Bruce Alexander is best known - though deserves to be much better known - for the 'Rat Park' experiments he conducted in 1981. As an addiction psychologist, much of the data with which he worked was drawn from laboratory trials with rats and monkeys: the 'addictiveness' of drugs such as opiates and cocaine was established by observing how frequently caged animals would push levers to obtain doses. But Alexander's observations of addicts at the clinic where he worked in Vancouver suggested powerfully to him that the root cause of addiction was not so much the pharmacology of these particular drugs as the environmental stressors with which his addicts were trying to cope.

To test his hunch he designed Rat Park, an alternative laboratory environment constructed around the need of the subjects rather than the experimenters. A colony of rats, who are naturally gregarious, were allowed to roam together in a large vivarium enriched with wheels, balls and other playthings, on a deep bed of aromatic cedar shavings and with plenty of space for breeding and private interactions. Pleasant woodland vistas were even painted on the surrounding walls. In this situation, the rats' responses to drugs such as opiates were transformed. They no longer showed interest in pressing levers for rewards of morphine: even if forcibly addicted, they would suffer withdrawals rather than maintaining their dependence. Even a sugar solution could not tempt them to the morphine water (though they would choose this if naloxone was added to block the opiate effects). It seemed that the standard experiments were measuring not the addictiveness of opiates but the cruelty of the stresses inflicted on lab rats caged in solitary confinement, shaved, catheterised and with probes inserted into their median forebrain bundles.