Reversal of cocaine addiction by environmental enrichment

Addiction is one of those topics where there's a lot of morally hysterical yelling that generates plenty of heat but no illumination. It's also an area where we're making rapid and interesting scientific progress. One battle that was -- to my mind -- won a long time ago involved getting addiction taken seriously as in key respects a behaviour like any other. That doesn't mean addictive behaviour isn't odd in some respects, but rather that like any other behaviour it is sensitive to opportunity cost.

This was a tough sell partly because much muddled thinking about addiction sees the activity of the addict as a departure from her normal agency - the addict was roughly supposed to be periodically and unconditionally enslaved to something else. A body of empirical work was done showing that consumption by addicts was sensitive to price - when booze costs more, drunks drink less. And also sensitive to opportunity cost - when booze costs the same, but additional substitutable products become available, so that what is being given up by drinking is more, drunks also drink less. The introduction to Rudy Vuchinich and Nick Heather's 2003 anthology Choice, Behavioral Economics and Addiction (Pergamon) provides a terrific overview of the relevant theory and results.

This paper adds very importantly to what we know. The paper reports that mice addicted to cocaine lose addictive symptoms when exposed to an "enriched environment" during withdrawal. Here's the abstract:

Environmental conditions can dramatically influence the behavioral and neurochemical effects of drugs of abuse. For example, stress increases the reinforcing effects of drugs and plays an important role in determining the vulnerability to develop drug addiction. On the other hand, positive conditions, such as environmental enrichment, can reduce the reinforcing effects of psychostimulants and may provide protection against the development of drug addiction. However, whether environmental enrichment can be used to "treat" drug addiction has not been investigated. In this study, we first exposed mice to drugs and induced addiction-related behaviors and only afterward exposed them to enriched environments. We found that 30 days of environmental enrichment completely eliminates behavioral sensitization and conditioned place preference to cocaine. In addition, housing mice in enriched environments after the development of conditioned place preference prevents cocaine-induced reinstatement of conditioned place preference and reduces activation of the brain circuitry involved in cocaine-induced reinstatement. Altogether, these results demonstrate that environmental enrichment can eliminate already established addiction-related behaviors in mice and suggest that environmental stimulation may be a fundamental factor in facilitating abstinence and preventing relapse to cocaine addiction.

So what did they do? Well, the addicted a group of mice to cocaine, and the split them into two sub-groups during withdrawal. Those in the "enriched environment" had larger enclosures with nicer shelters, a running wheel, and access to toys that were changed weekly.

They studied three different measures of addiction, each in a separate experiment:

(1) Behavioural sensitisation, which is a measure of the increase in effects of cocaine following chronic administration.
(2) Location preference, which is a measure of the extent to which a previously learned spatial association continues to elicit drug-seeking behaviour.
(3) The propensity of cocaine administration to lead to relapse after withdrawal.

The result was dramatic - after 30 days of exposure to the "enriched environment" addiction behavior of all three kinds had disappeared.

In contrast, the mice in the non-enriched environment still showed measurable addiction on each model after 30 days.

What has been found here isn't that availability of substitutable 'alternatives' makes a difference to the course of addiction. First, we knew that already. Second, the mice in the "enriched environment" weren't chosing between play and cocaine, so that the availability of play raised the opportunity cost of cocaine. They had more options during withdrawal.

The authors suggest two possible mechanisms. First, the "enriched environment" was less stressful, and stress is know to mediate relapse and drug-seeking. Second, the "enriched environment" provided opportunities to learn a wider range of reward-seeking behaviours, which reduced the power of the previously learned patterns relative to controls which had fewer such opportunities. These are not mutually exclusive, and both seem highly plausible (there's also independent evidence for each).

There's plenty more to be found out, but this is a very useful addition to our understanding. For another brief notice of the same research see this on Science Daily.

M. Solinas, C. Chauvet, N. Thiriet, R. El Rawas, M. Jaber (2008). From the Cover: Reversal of cocaine addiction by environmental enrichment Proceedings of the National Academy of Sciences, 105 (44), 17145-17150 DOI: 10.1073/pnas.0806889105