Rat Park never replicated. Rats still choose company over heroin.

Rat Park, the famous proof that addiction is loneliness, never replicated. A 2018 study found something sturdier: rats choose company over heroin.

In the late 1970s, at Simon Fraser University near Vancouver, Bruce Alexander and three colleagues built their rats a better life. Instead of the usual small metal cage, they got an enclosure about two hundred times the floor area, with balls and running wheels, room to mate, and sixteen to twenty other rats. Then the researchers offered the rats morphine dissolved in sugar water and compared how much they drank against rats living alone in standard cages.

The paper that came out of it in 1981, in Pharmacology Biochemistry and Behavior, is short and careful. Rats living in the colony when they were tested drank less of the morphine solution than isolated rats, and no less of the sweet control drinks. Colony rats that had spent their youth in isolation drank somewhat more than those raised in the park, but that difference was statistically clear only at the weakest morphine concentration. The authors' own explanation was modest: morphine gets in the way of the complicated social life a rat has in a colony, so colony rats avoid it.

Thirty-four years later that modest result had become a slogan. In a TED talk in 2015 the journalist Johann Hari summed up the lesson in two sentences: "The opposite of addiction is not sobriety. The opposite of addiction is connection." An animated video that the YouTube channel Kurzgesagt made with Hari the same year became one of the channel's most popular at the time. The idea is appealing for a site like this one. If addiction is mostly loneliness, then good neighbours are a kind of medicine.

So it is worth knowing what happened when someone tried to run the experiment again.

The replication that went the wrong way

Bruce Petrie, a former student of Alexander's, repeated the housing experiment twice and published the results in Psychological Reports in 1996. His title is the whole finding: "Environment is not the most important variable in determining oral morphine consumption in Wistar rats." In his words, the earlier result "could not be replicated", because this time the isolated rats drank less. Petrie suspected the rats themselves had changed. The supplier had rebuilt its breeding colony in the meantime, and he thought a genetic difference might have crept in.

Another team, Michael Bozarth, A. Murray and Roy Wise at Concordia University in Montreal, had tested a related question in 1989 with rats that pressed a lever for intravenous heroin or cocaine. Isolated rats learned to take heroin a little sooner, but by the fifth week both groups were taking about the same amount. With cocaine there was no difference at all. Their conclusion was that isolation "can influence" heroin use but is not needed for the drugs to be rewarding.

Look at the originals with today's eyes and the problems pile up. The groups were small. Morphine is bitter, so drinking it in sugar water measures taste as well as craving. Consumption was measured differently in the cages and in the park. In 2019 Kurzgesagt took its addiction video down, saying it had not met the channel's current standards. And in 2020 Shaun Khoo, reviewing the whole story for the Journal for Reproducibility in Neuroscience, wrote plainly that the Rat Park studies "have not been successfully replicated directly".

That would be the end of a debunking article. It is not the end of this one.

The rats who got to choose

Khoo's review has a second half. A long line of studies from the same era and after has found that social and physical enrichment makes rats and mice less drawn to drugs. There are also studies that found no such effect, and genes, sex, age and the drug itself all turn out to matter. His verdict is that Rat Park was not reproduced, but the general idea behind it was: "conceptual but not direct replication".

The strongest piece of that conceptual evidence came in 2018 from Marco Venniro, Yavin Shaham and colleagues at the US National Institute on Drug Abuse, published in Nature Neuroscience. They did something Rat Park never did: they gave rats a choice. In one chamber a rat could press one lever for a dose of heroin or methamphetamine, and another lever to open a sliding door and spend a minute with another rat. The study used 222 rats as choosers, male and female.

The rats chose company. They did so across drug types and doses, after different training schedules, and even when they had scored high on a measure of addiction modelled on the diagnostic criteria used for people. Rats that stopped taking methamphetamine because they preferred the social lever also showed less of the craving that normally grows during abstinence.

There was a limit, and the authors reported it. When the social reward came only after a long delay, or when pressing that lever brought an electric shock to the feet, the rats went back to the drug. Company worked when it was available now and without a price.

What survives

What survives is smaller than the slogan and still worth a lot. A lonely cage makes drugs more attractive for a rat, sometimes, depending on the rat. A friend behind a door that opens straight away is, for most rats most of the time, worth more than heroin. That second finding is the one the researchers themselves turned towards people. They wrote that it supports wider use of social treatments for addiction, including the community reinforcement approach, where a person's life outside the drug is deliberately made more rewarding.

Nobody has shown that loneliness causes addiction in humans the way the TED version says. The evidence does suggest something more practical. Help that is close by and quick to reach may matter more than help that is excellent and far away, and a person who is slipping is easier to reach through someone they already know.

That is roughly what a neighbourhood can offer. Not a cure. A door that opens when someone knocks. We have written before about another famous number in social science, Dunbar's number came back as anything from 2 to 520, and it went a similar way: the tidy number fell apart, and what was left was slower, more useful advice about watching the group you actually have.

Sources

• B. K. Alexander, B. L. Beyerstein, P. F. Hadaway, R. B. Coambs, "Effect of early and later colony housing on oral ingestion of morphine in rats", Pharmacology Biochemistry and Behavior 15(4), 571–576, 1981 — https://doi.org/10.1016/0091-3057(81)90211-2
• B. F. Petrie, "Environment is not the most important variable in determining oral morphine consumption in Wistar rats", Psychological Reports 78(2), 391–400, 1996 — https://doi.org/10.2466/pr0.1996.78.2.391
• M. A. Bozarth, A. Murray, R. A. Wise, "Influence of housing conditions on the acquisition of intravenous heroin and cocaine self-administration in rats", Pharmacology Biochemistry and Behavior 33(4), 903–907, 1989 — https://doi.org/10.1016/0091-3057(89)90490-5
• S. Y.-S. Khoo, "Have we reproduced Rat Park? Conceptual but not direct replication of the protective effects of social and environmental enrichment in addiction", Journal for Reproducibility in Neuroscience 1, 2020 — https://doi.org/10.31885/jrn.1.2020.1318
• M. Venniro et al., "Volitional social interaction prevents drug addiction in rat models", Nature Neuroscience 21, 1520–1529, 2018 — https://doi.org/10.1038/s41593-018-0246-6
• J. Hari, "Everything you think you know about addiction is wrong", TED talk, 2015 — https://www.ted.com/talks/johann_hari_everything_you_think_you_know_about_addiction_is_wrong
• Kurzgesagt, "Can You Trust Kurzgesagt Videos?", 2019 — https://www.youtube.com/watch?v=JtUAAXe_0VI
• S. H. Gage, H. R. Sumnall, "Rat Park: How a rat paradise changed the narrative of addiction", Addiction, 2018 — https://doi.org/10.1111/add.14481