Rat Park
Rat Park was a study into drug addiction conducted in the late 1970s (and published in 1980), by Canadian psychologist Bruce K. Alexander and his colleagues at Simon Fraser University
Simon Fraser University
Simon Fraser University is a Canadian public research university in British Columbia with its main campus on Burnaby Mountain in Burnaby, and satellite campuses in Vancouver and Surrey. The main campus in Burnaby, located from downtown Vancouver, was established in 1965 and has more than 34,000...

 in British Columbia, Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...


Alexander's hypothesis was that drugs do not cause addiction, and that the apparent addiction to opiate
In medicine, the term opiate describes any of the narcotic opioid alkaloids found as natural products in the opium poppy plant.-Overview:Opiates are so named because they are constituents or derivatives of constituents found in opium, which is processed from the latex sap of the opium poppy,...

 drugs commonly observed in laboratory rats exposed to it is attributable to their living conditions, and not to any addictive property of the drug itself. He told the Canadian Senate
Canadian Senate
The Senate of Canada is a component of the Parliament of Canada, along with the House of Commons, and the monarch . The Senate consists of 105 members appointed by the governor general on the advice of the prime minister...

 in 2001 that prior experiments in which laboratory rats were kept isolated in cramped metal cages, tethered to a self-injection apparatus, show only that "severely distressed animals, like severely distressed people, will relieve their distress pharmacologically
Pharmacology is the branch of medicine and biology concerned with the study of drug action. More specifically, it is the study of the interactions that occur between a living organism and chemicals that affect normal or abnormal biochemical function...

 if they can."

To test his hypothesis, Alexander built Rat Park, an 8.8 m² (94.7 sq ft) housing colony, 200 times the square footage of a standard laboratory cage. There were 16–20 rats of both sexes in residence, an abundance of food, balls and wheels for play, and enough space for mating
In biology, mating is the pairing of opposite-sex or hermaphroditic organisms for copulation. In social animals, it also includes the raising of their offspring. Copulation is the union of the sex organs of two sexually reproducing animals for insemination and subsequent internal fertilization...

 and raising litters. The results of the experiment appeared to support his hypothesis
A hypothesis is a proposed explanation for a phenomenon. The term derives from the Greek, ὑποτιθέναι – hypotithenai meaning "to put under" or "to suppose". For a hypothesis to be put forward as a scientific hypothesis, the scientific method requires that one can test it...

. Rats who had been forced to consume morphine hydrochloride for 57 consecutive days were brought to Rat Park and given a choice between plain tap water and water laced with morphine. For the most part, they chose the plain water. "Nothing that we tried," Alexander wrote, "... produced anything that looked like addiction in rats that were housed in a reasonably normal environment." Control groups of rats isolated in small cages consumed much more morphine in this and several subsequent experiments.

The two major science journals, Science
Science (journal)
Science is the academic journal of the American Association for the Advancement of Science and is one of the world's top scientific journals....

 and Nature
Nature (journal)
Nature, first published on 4 November 1869, is ranked the world's most cited interdisciplinary scientific journal by the Science Edition of the 2010 Journal Citation Reports...

, rejected Alexander, Coambs, and Hadaway's first paper, which appeared instead in Psychopharmacology, a respectable but much smaller journal in 1978. The paper's publication initially attracted no response. Within a few years, Simon Fraser University withdrew Rat Park's funding.

The disease model of drug addiction

It is not disputed that some substances cause withdrawal symptoms after repeated use, leaving the user in distress if they stop using. Where scientists differ is over the extent to which certain substances can be said to rob the user of self control
Self control
Self control is the ability to control one's emotions, behavior and desires in order to obtain some reward later. In psychology it is sometimes called self-regulation...

, causing not only withdrawal— but a drug addiction, defined as "a behavioral pattern of drug use, characterized by overwhelming involvement with the use of a drug (compulsive use), the securing of its supply, and a high tendency to relapse after withdrawal."

In the 19th century, drug addiction was regarded as a sign of akrasia
Akrasia , occasionally transliterated as acrasia, is the state of acting against one's better judgment. The adjective form is "akratic".-Classical approaches:...

, immorality, or weakness of the will. However 20th century brain research replaced this moral model with a disease model of addiction
Disease model of addiction
The disease model of addiction describes an addiction as a lifelong disease involving biologic and environmental sources of origin. The traditional medical model of disease requires only that an abnormal condition be present that causes discomfort, dysfunction, or distress to the individual...

, according to which addiction to a drug is a by-product of the chemical
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....

 structure of the drug itself. According to social psychologist Stanton Peele, the disease model states that "[t]olerance, withdrawal, and craving are thought to be properties of particular drugs, and sufficient use of these substances is believed to give the organism no choice but to behave in these stereotypical ways." This view of drug addiction is reflected in the policies of the War on Drugs
War on Drugs
The War on Drugs is a campaign of prohibition and foreign military aid and military intervention being undertaken by the United States government, with the assistance of participating countries, intended to both define and reduce the illegal drug trade...

 and in slogans such as "Heroin is so good. Don't even try it once," or "Crack cocaine
Crack cocaine
Crack cocaine is the freebase form of cocaine that can be smoked. It may also be termed rock, hard, iron, cavvy, base, or just crack; it is the most addictive form of cocaine. Crack rocks offer a short but intense high to smokers...

 is instantly addictive."

Scientists adhering to the disease model believe that behavior is "the business of the brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...

," according to Avram Goldstein, Professor Emeritus of Pharmacology
Pharmacology is the branch of medicine and biology concerned with the study of drug action. More specifically, it is the study of the interactions that occur between a living organism and chemicals that affect normal or abnormal biochemical function...

 at Stanford University
Stanford University
The Leland Stanford Junior University, commonly referred to as Stanford University or Stanford, is a private research university on an campus located near Palo Alto, California. It is situated in the northwestern Santa Clara Valley on the San Francisco Peninsula, approximately northwest of San...

, and a leading researcher into drug addiction. Goldstein writes that the site of action of heroin and all other addictive drugs is a bundle of neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...

s deep in the brain called the mesolimbic dopaminergic pathway
Mesolimbic pathway
The mesolimbic pathway is one of the dopaminergic pathways in the brain. The pathway begins in the ventral tegmental area of the midbrain and connects to the limbic system via the nucleus accumbens, the amygdala, and the hippocampus as well as to the medial prefrontal cortex...

, a reward pathway
Dopaminergic pathways
Dopaminergic pathways are neural pathways in the brain which transmit the neurotransmitter dopamine from one region of the brain to another.The neurons of the dopaminergic pathways have axons which run the entire length of the pathway...

 that mediates feelings of wanting and motivation
Motivation is the driving force by which humans achieve their goals. Motivation is said to be intrinsic or extrinsic. The term is generally used for humans but it can also be used to describe the causes for animal behavior as well. This article refers to human motivation...

. Within this pathway, heroin causes dopamine
Dopamine is a catecholamine neurotransmitter present in a wide variety of animals, including both vertebrates and invertebrates. In the brain, this substituted phenethylamine functions as a neurotransmitter, activating the five known types of dopamine receptors—D1, D2, D3, D4, and D5—and their...

A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...

s to release dopamine, a neurotransmitter
Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to...

 that determines incentive salience
Incentive salience
Incentive salience is a motivational "wanting" attribute given by the brain to reward-predicting stimuli. This "wanting" is unlike "liking" in that liking is a pleasure immediately gained from consumption or other contact with stimuli, while the "wanting" of incentive salience is a motivational...

 and causes the user to want more. Dopamine neurons are normally held in check by inhibitory neurons, but heroin shuts these down, allowing the dopamine neurons to become overstimulated. The brain responds with feelings of euphoria
Euphoria (emotion)
Euphoria is medically recognized as a mental and emotional condition in which a person experiences intense feelings of well-being, elation, happiness, ecstasy, excitement and joy...

, but the stimulation is excessive, and in order to protect itself against this, the brain adapts by becoming less sensitive to the heroin.

This has two consequences, according to the disease model. First, more heroin is required to produce the high, and at the same time, the reward pathway becomes less sensitive to the effects of endorphin
Endorphins are endogenous opioid peptides that function as neurotransmitters. They are produced by the pituitary gland and the hypothalamus in vertebrates during exercise, excitement, pain, consumption of spicy food, love and orgasm, and they resemble the opiates in their abilities to produce...

s, which regulate the release of dopamine, so that without heroin, there is a persistent feeling of sickness. After repeated intake, the user becomes tolerant and dependent, and undergoes withdrawal symptoms if the heroin supply is terminated. As the feelings of withdrawal worsen, the user loses control, writes Goldstein, and becomes an addict.

Studies of isolated laboratory animals generally support the disease model

According to Alexander, the disease model makes either of two claims:
  • Claim A: All or most people who use heroin or cocaine beyond a certain minimum amount become addicted.
  • Claim B: No matter what proportion of the users of heroin and cocaine become addicted, their addiction is caused by exposure to the drug.

Several decades of animal studies
Animal testing
Animal testing, also known as animal experimentation, animal research, and in vivo testing, is the use of non-human animals in experiments. Worldwide it is estimated that the number of vertebrate animals—from zebrafish to non-human primates—ranges from the tens of millions to more than 100 million...

 have been seen as supporting these claims. Avram Goldstein wrote in 1979: "If a monkey is provided with a lever, which he can press to self-inject heroin, he establishes a regular pattern of heroin use — a true addiction — that takes priority over the normal activities of his life ... Since this behavior is seen in several other animal species (primarily rats), I have to infer that if heroin were easily available to everyone, and if there were no social pressure of any kind to discourage heroin use, a very large number of people would become heroin addicts.

Twenty years later, Goldstein maintains the same position. In a paper delivered to a 1997 U.S. methadone
Methadone is a synthetic opioid, used medically as an analgesic and a maintenance anti-addictive for use in patients with opioid dependency. It was developed in Germany in 1937...

 conference, he wrote: "Every addictive drug used by people is also self-administered by rats and monkeys. If we arrange matters so that when an animal presses a lever, it gets a shot of heroin into a vein, that animal will press the lever repeatedly, to the exclusion of other activities (food, sex, etc.); it will become a heroin addict. A rat addicted to heroin is not rebelling against society, is not a victim of socioeconomic circumstances, is not a product of a dysfunctional family, and is not a criminal. The rat's behavior is simply controlled by the action of heroin (actually morphine
Morphine is a potent opiate analgesic medication and is considered to be the prototypical opioid. It was first isolated in 1804 by Friedrich Sertürner, first distributed by same in 1817, and first commercially sold by Merck in 1827, which at the time was a single small chemists' shop. It was more...

, to which heroin is converted in the body) on its brain."

Against this, Alexander argues that the main evidence for the belief in drug-induced addiction comes from "the testimonials of some addicted people who believe that exposure to a drug caused them to 'lose control'," and from some "highly technical research on laboratory animals". He argues that this weak evidence has been embellished in the news media to the point where it has acquired the status of an unassailable fact, whereas the great bulk of historical and clinical evidence, he says, runs against it. He writes that, although the use of opiates in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 and England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

 during the 19th century was greater than it is now, the incidence of dependence and addiction never reached one percent of the population and was declining at the end of the century. In Britain, he writes that heroin has been widely used in medication for cough
A cough is a sudden and often repetitively occurring reflex which helps to clear the large breathing passages from secretions, irritants, foreign particles and microbes...

s, diarrhea
Diarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...

, and chronic pain
Chronic pain
Chronic pain has several different meanings in medicine. Traditionally, the distinction between acute and chronic pain has relied upon an arbitrary interval of time from onset; the two most commonly used markers being 3 months and 6 months since the initiation of pain, though some theorists and...

 until the present day; in 1972, British doctors prescribed 29 kilograms of heroin to patients, which he writes amounts to millions of doses, yet a 1982 study of the statistics on iatrogenic
Iatrogenesis, or an iatrogenic artifact is an inadvertent adverse effect or complication resulting from medical treatment or advice, including that of psychologists, therapists, pharmacists, nurses, physicians and dentists...

 addiction in the UK showed a "virtual absence" of such addicts. Recent research confirms that many people use heroin regularly for years, for either recreational or medical purposes, without becoming addicted.

The Rat Park experiments

In Rat Park, Alexander built a short tunnel large enough to accommodate one rat at a time. At the far end of the tunnel, the rats could drink a fluid from one of two drop dispensers, which automatically recorded how much each rat drank. One dispenser contained a morphine solution and the other plain tap water
Tap water
Tap water is a principal component of "indoor plumbing", which became available in urban areas of the developed world during the last quarter of the 19th century, and common during the mid-20th century...


Alexander designed a number of experiments to test the rats' willingness to consume the morphine. Rats have a sweet tooth, so in "The Seduction Experiment," the researchers exploited the rats' apparent sweet tooth to test whether they could be enticed to consume morphine if the water was sweet enough. Morphine in solution has a bitter taste for humans, and appears to have the same effect on rats, Alexander writes, since they shake their heads and reject it as they do with bitter quinine solutions. The Seduction Experiment involved four groups of rats. Group CC was isolated in laboratory cages when they were weaned at 22 days of age, and lived there until the experiment ended at 80 days of age; Group PP was housed in Rat Park for the same period; Group CP was moved from laboratory cages to Rat Park at 65 days of age; and Group PC was moved out of Rat Park and into cages at 65 days of age.

The caged rats (Groups CC and PC) took to the morphine instantly, even with relatively little sweetener, with the caged males drinking 19 times more morphine than the Rat Park males in one of the experimental conditions. But no matter how sweet the morphine became, the rats in Rat Park resisted it. They would try it occasionally — with the females trying it more often than the males — but invariably they showed a preference for the plain water. It was, writes Alexander, "a statistically significant
Statistical significance
In statistics, a result is called statistically significant if it is unlikely to have occurred by chance. The phrase test of significance was coined by Ronald Fisher....

 finding." He writes that the most interesting group was Group CP, the rats who were brought up in cages but moved to Rat Park before the experiment began. These animals rejected the morphine solution when it was stronger, but as it became sweeter and more dilute, they began to drink almost as much as the rats that had lived in cages throughout the experiment. They wanted the sweet water, he concluded, so long as it did not disrupt their normal social behavior. Even more significant, he writes, was that when he added a drug called Naloxone
Naloxone is an opioid antagonist drug developed by Sankyo in the 1960s. Naloxone is a drug used to counter the effects of opiate overdose, for example heroin or morphine overdose. Naloxone is specifically used to counteract life-threatening depression of the central nervous system and respiratory...

, which negates the effects of opioids, to the morphine-laced water, the Rat Park rats began to drink it.

In another experiment, he forced rats in ordinary lab cages to consume morphine for 57 days on end, giving them no liquid to drink other than the morphine-laced solution, then moved them into Rat Park, where he allowed them to choose between the morphine solution and plain water. They drank the plain water. He writes that they did show some signs of dependence, but no sign of addiction. There were "some minor withdrawal signs, twitching, what have you, but there were none of the mythic seizures and sweats you so often hear about ..."

Alexander believes his experiments show that animal self-administration studies provide no empirical
Empiricism is a theory of knowledge that asserts that knowledge comes only or primarily via sensory experience. One of several views of epistemology, the study of human knowledge, along with rationalism, idealism and historicism, empiricism emphasizes the role of experience and evidence,...

 support for the theory of drug-induced addiction, and that the theory has no other strong basis in empirical science, although it has not been disproven. "The intense appetite of isolated experimental animals for heroin and cocaine in self-injection experiments tells us nothing about the responsiveness of normal animals and people to these drugs. Normal people can ignore heroin ... even when it is plentiful in their environment, and they can use these drugs with little likelihood of addiction ... Rats from Rat Park seem to be no less discriminating."

Reaction to the experiment

The two major science journals Science
Science (journal)
Science is the academic journal of the American Association for the Advancement of Science and is one of the world's top scientific journals....

 and Nature
Nature (journal)
Nature, first published on 4 November 1869, is ranked the world's most cited interdisciplinary scientific journal by the Science Edition of the 2010 Journal Citation Reports...

 rejected Alexander's first paper, which was published in Psychopharmacology, a specialty journal. Several later studies did appear to confirm its findings — for example, Bozarth, Murray and Wise in 1989, also published in Pharmacology, Biochemistry and Behavior — but nothing came of those either. Writer Lauren Slater
Lauren Slater
Lauren Slater is an American psychologist and writer. She is the author of six books, including Welcome To My Country , Prozac Diary , and Lying: A Metaphorical Memoir...

, Alexander's daughter-in-law, interviewed psychiatrist
Psychiatry is the medical specialty devoted to the study and treatment of mental disorders. These mental disorders include various affective, behavioural, cognitive and perceptual abnormalities...

 Herbert Kleber
Herbert Kleber
Herbert D. Kleber, M.D., has been a pioneer in research and treatment of substance abuse for over 35 years. From 1968 to 1989, he founded and headed the Drug Dependence Unit at Yale University, where he was Professor of Psychiatry. He then served for 2 ½ years as the Deputy Director for Demand...

, director of the substance-abuse division of the College of Physicians and Surgeons of Columbia University
Columbia University
Columbia University in the City of New York is a private, Ivy League university in Manhattan, New York City. Columbia is the oldest institution of higher learning in the state of New York, the fifth oldest in the United States, and one of the country's nine Colonial Colleges founded before the...

, and a former U.S. deputy drug czar
Drug Czar
Drug Czar is an informal name for the person who directs drug-control policies in the United States, following the U.S. use of the 'czar' term. The 'drug czar' title was first published in a 1982 news story by United Press International which reported that “Senators... voted 62–34 to establish a...

, on what was wrong with Rat Park. He replied that the experiment was "ingenious," but suggested that Alexander may have distorted the data in the hope of provoking a public debate, and that the study had methodological
Methodology is generally a guideline for solving a problem, with specificcomponents such as phases, tasks, methods, techniques and tools . It can be defined also as follows:...

 flaws, though he did not state examples. Slater believes Rat Park's problem was that it was conducted in Vancouver
Vancouver is a coastal seaport city on the mainland of British Columbia, Canada. It is the hub of Greater Vancouver, which, with over 2.3 million residents, is the third most populous metropolitan area in the country,...

, the "scholarly equivalent of the tundra."

While the original experiment's results were not always reproduced (though in this case, both caged and "park" rats showed a decreased preference for morphine, suggesting a genetic difference), the publications did draw attention to the idea that the environment that laboratory animals live in might influence the outcome in experiments related to addiction. , papers from the series of experiments have been cited more than 100 times, and similar studies on the influence of living conditions on the consumption of other drugs have been published.

Alexander was disappointed by the reception, and still speaks of the experiments enthusiastically. Since 1985, Alexander has been exploring addiction in human beings by way of historical and anthropological studies of many cultures. His newest book, "The Globalisation of Addiction: A study in poverty of the spirit" argues that cultural dislocation of human beings instigates addictions of all sorts, including addictions that do not involve drugs, just as isolation instigates drug consumption in laboratory animals.

Related research

Recent research has shown that an enriched environment
Environmental enrichment (neural)
Environmental enrichment concerns how the brain is affected by the stimulation of its information processing provided by its surroundings . Brains in richer, more stimulating environments, have increased numbers of synapses, and the dendrite arbors upon which they reside are more complex...

may decrease morphine addiction in mice. Enriched environments also decrease deficits in animal models of Parkinson's disease, Huntington's disease, and Alzheimer's disease.

Further reading

  • Alexander, B.K., Beyerstein, B.L., Hadaway, P.F., and Coambs, R.B. (1981) "Effect of early and later colony housing on oral ingestion of morphine in rats," Pharmacology Biochemistry and Behavior, Vol 15, 4:571–576. PMID 7291261
  • Alexander, B.K. (1985) "Drug use, dependence, and addiction at a British Columbia university: Good news and bad news," Canadian Journal of Higher Education, 15, 77–91.
  • Alexander, B.K. (1987) "The disease and adaptive models of addiction: A framework evaluation," Journal of Drug Issues 17, pp. 47–66.
  • Alexander, B.K. (1990) Peaceful measures: Canada's way out of the War on Drugs, Toronto University Press. ISBN 0-8020-6753-0
  • Alexander, B.K. (2000) "The globalization of addiction," Addiction Research
  • Drucker, E. (1998) "Drug Prohibition and Public Health," U.S. Public Health Service, Vol. 114
  • Goldstein, A. Molecular and Cellular Aspects of the Drug Addictions. Springer-Verlag, 1990. ISBN 0-387-96827-X
  • Goldstein, A.From Biology to Drug Policy, Oxford University Press, 2001. ISBN 0-19-514664-6
  • Website of the U.S. Office of National Drug Control Policy
  • Peele, Stanton. A discussion about addiction, archived link from July 7, 2004.
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