Rat Park – challenging ideas about addiction

Like many university psychology departments the School of Psychology at Keele University, where I am based, has a lunchtime speaker series. Other psychologists are invited to come and talk for an hour about their research followed by questions and answers. The audience for these events is often quite mixed. The largest group consists of the postgraduate students. At Keele this group is required to attend for course credit. There is a smattering of school academic staff – the usual faces – usually older members of staff. There are two or three unfamiliar faces that one presumes are staff or postgraduate students from other parts of the university. I’m one of the few regulars at these events and when a colleague recently asked why that was, I had to stop and think. I developed the habit years ago in response to an e-mail sent round by the then head of school pleading for more academics to attend these out of embarrassment. It doesn’t look that good when the visiting speaker is confronted by an underwhelmingly empty room. That I have carried on coming is because I enjoy these sessions immensely, on many different levels. In fact I find them a little like listening to live music. Listening can be wonderful and inspiring; it can contain an idea that chimes with your own work and sets you thinking down different avenues; it can be mediocre and as my mind wanders it usually alights on my own research and has lead to some interesting ideas completely disconnected from the speaker; finally, very occasionally, it can be so bad that you can take heart that no matter what you ever do in a public sphere you would never be this dire!

A recent presentation by psychologist Dr Martin Frisher of Keele’s School of Pharmacy was of the wonderful and inspiring variety. I could see on entering the room that this would be different to usual because there was a smattering of undergraduate psychology students down near the front. Very unusual. From the start Martin’s talk was interesting but I still was not expecting to have a fundamental belief about drug addiction turned on its head. Yet that’s what happened when Martin talked about the Rat Park experiments, something I had not previously been aware of. The Rat Park story goes like this:

Bruce K Alexander and colleagues from Simon Fraser University in Canada wondered about heroin addiction. Data from animal studies was being used in the 1970s to support the argument that the drug heroine has fundamentally addictive properties. That is, most people who take heroine beyond a certain minimum amount, will become uncontrollably addicted to it. The argument was based on studies from the 1950s, 1960s and 1970s showing that laboratory rats given the choice of the naturally occurring opiate from which heroin is synthesised, morphine, or clean water, will more often choose morphine. Remarkably, nobody prior to Alexander thought to investigate whether the environmental conditions in which these experiments took place might have any bearing on the results. And yet, there was good reason to look at housing conditions. As Alexander explains in the 1978 paper that is the subject of this blog, rats are gregarious, wide ranging and curious creatures, and as a consequence would be very likely to find unpleasant the small solitary cages routinely employed in science laboratories. Alexander and colleagues asked whether rats kept under such conditions used morphine to self-medicate in response to the stress of being in such an unnatural environment. To test this out they set out to construct the least confining laboratory housing for rats that they could make.

They devised a large open topped wooden box with 9 square meters of floor space, including living areas and a climbing pole. Placed into this were 22 rats that had just been weaned and were free to explore this socially and spatially rich environment, which became know as “Rat Park”. Not so lucky were the 12 control condition rats. Similarly aged, these rats were placed, from weaning, into solitary small cages whose metal walls prevented visual contact with neighbouring creatures. Both groups had access to clean water and a morphine solution. Drinking behaviour was monitored using video cameras and electronic counters controlled with light beams. Over the following weeks, access to the morphine was controlled according to several different procedures designed to mimic different stages of drug addiction in humans.

Initially the rats could choose water or morphine on some days, or on other days they had access only to morphine. Given the choice, most of the rats, regardless of condition chose not to have morphine. For the next 6 weeks, in order to mimic drug addicts taking a drug for a prolonged period, the rats were provided only with morphine. Both groups consumed morphine, indicating that this procedure was effective in guiding the rats to become drug users. However, on several test days a choice was allowed to determine the rats’ preference for morphine or clean water. On these days, the isolated rats went on taking morphine while the social rats cut back significantly. Indeed, the amount of morphine consumed on choice days was demonstrably larger in the isolated rats. For the next 4 weeks a schedule in which availability of water and morphine was alternated was used, based on previous research showing that this schedule (the so-called “Nichols Cycle”) was effective in guiding already addicted rats to increase morphine consumption. Again both groups drank substantial quantities of morphine during this schedule, and on several choice days where morphine and clean water were provided, again the isolated rats went on taking morphine. On the other hand, the socially housed rats cut back on morphine when they could choose clean water. The experiment finished with a morphine abstinence period lasting 5 weeks in which only clean water was provided to drink, although two opportunities to choose morphine were presented. Once again, the isolated rats consumed far more morphine than the social rats on these days.

Alexander interpreted the findings as showing that housing conditions actually do appear to play an important role in determining when rats will choose to take the drug morphine. Even though all the rats in the study were guided into becoming “users”, on the days when the rats could choose between morphine solution or clean water, the isolated rats were much more likely to continue taking morphine than the rats living in the more sociable surroundings of rat park. It is suggested that the social rats avoided morphine where possible because it interfered with their natural activity patterns. However, because these natural activities were already substantially curtailed by isolation, the rats in the small cages continued to take the morphine when it was available. The usual explanation for addiction to morphine or heroine is that users persist in taking the drug to avoid unpleasant withdrawal effects. However, such effects should be independent of living conditions, and the impact of the home environment in the rat park study indicates that perhaps classic medical ideas about addiction need to be revised.

You might think that such a breakthrough finding would have changed thinking about drug use and drug addiction over the coming decades, and that the rat park experiments would have taken their place among the most celebrated pieces of psychology research, such as Milgram’s electric shock research and the Stanford Prison experiment. However, this is far from the truth. Alexander struggled to secure publication of the research, and funding of his lab was withdrawn by Simon Fraser University within a few years. It seems that researching addiction has a political dimension unwelcoming of challenges to the still-prevailing medical model of addiction. Alexander sticks by his controversial ideas, delivering a paper to the Canadian Senate in 2001 entitled “The myth of drug-induced addiction”.

Still, have no doubt, this is cool psychological research. It has an elegance with clear objectives and a straightforward design to test them. Both the findings and their interpretation are easy to understand and yet have a massive impact on the still socially devastating problem of drug use and addiction. The simplest ideas are often the best. All it took was for someone to think of giving lab rats a larger cage with other rats and seemingly unchallengeable ideas were called into question. The Cool Psychology blog salutes the Rat Park experiments.

The full reference to the original rat park study is included below. While a more recent 1980 paper is more widely available on the world wide web, the original 1978 paper is harder to come by. My university did not have a subscription to the journal Psychopharmacology so I had to pay £6 to have my university library order a photocopy from the British Library using its Library Privilege service (otherwise known as the Inter-Library Loans system). Though more expensive than several years ago this is an amazing service. For a relatively small sum you can obtain a copy of any research paper ever published, delivered in one week. Very cool.

Alexander, B.K., Coambs, R.B & Hadaway, P.F.(1978). The effect of housing and gender on morphine self-administration in rats. Psychopharmacology 58, 175-179.

Richard Stephens

July 2011