More than twenty years ago, however, a psychologist at Simon Frasier University suggested that these sorts of studies have a major flaw in their basic experimental design. Rats used in scientific study are generally kept individually in tiny cages, cut off from the extensive social contact that rats in the wild are known for. They are often given little or no physical or mental stimulation. In other words, the life of a lab rat (specifically in physiological, neurological and pharmacological studies) is a dreary one.

The psychologist in question, Bruce Alexander, hypothesized that the drug addiction seen in lab rats when they are exposed to drugs (for example morphine, which is what heroin is converted into in the body) might not arise solely or primarily from the properties of the drugs themselves, as people assumed. Rather, he suggested that perhaps it was because the rats' lives were so unpleasant that they went back to the offered drugs over and over.

So he set up Rat Park, a very large, semi-natural housing colony for lab rats (two hundred times the size of a normal cage), stocked with food and toys and other rats. Then he offered the rats a typical morphine solution alongside their normal water, giving them the choice to use the morphine or not. He sweetened the morphine water (rats love sweetened water), and even got a number of rats started by forcing them to use morphine for two months.

Amazingly enough, his results showed that the rats in this enriched park chose to intake significantly less of the morphine solution than rats in normal housing conditions (as little as one twentieth as much). This seems to suggest that rats kept in cramped cages choose to self-administer drugs because their lives are boring or painful, not necessarily or primarily because their initial exposure to the drugs got them addicted.

If the findings of this experiment are reliable (pending further replication and extension of the study, which was published in a peer-reviewed journal but did not catch on), then it suggests that much of the scientific study done on the subject of human drug addiction by studying lab rats could be inaccurate or incomplete. Considering how ubiquitous such studies are in neuroscience, biology, psychology, pharmacology and other departments in universities (not to mention private research institutions), this would be a major deal, and could have implications for social policy that is often based on those findings.

Furthermore, it is possible that cramped housing of rats and other laboratory animals has an even wider effect than just studies involving behavior like drug addiction. What the Rat Park experiment suggests is that lab animals can be in a better or worse state ('happier' or more 'depressed' in simple terms) depending on their living conditions. If psychological well-being has some effect on an animal's physiological state (much like stress has been shown to make ulcers worse, even though it does not cause ulcers), then even studies of the physiological effect of drugs (as opposed to behavior where there is a choice, like whether or not to self-administer morphine) could be biased by this variable.

So regardless of any moral arguments as to the ethical treatment of laboratory animals, this seems to suggest that there is solid scientific reason to improve the conditions of animals and keep their psychological well-being in mind when housing and working with them. For if we are to generalize the results of animal-testing studies to human beings (as has been crucial to the development of medicine in the past), we cannot afford results that are based on inadequate models, that tell us only how a depressed and unhealthy mammal will behave in a given situation.