Smoking while investing doesn't compute

by William Atkins

Sunday, 16 March 2008

Page 2 of 2

In the abstract to the researchers’ paper, they begin by saying, “Addicted individuals pursue substances of abuse even in the clear presence of positive outcomes that may be foregone and negative outcomes that may occur.”

Background information includes “Computational models of addiction depict the addicted state as a feature of a valuation disease, where drug-induced reward prediction error signals steer decisions toward continued drug use. Related models admit the possibility that valuation and choice are also directed by 'fictive' outcomes (outcomes that have not been experienced) that possess their own detectable error signals.”

The researchers used a simple game and fMRI scans: “We hypothesize that, in addiction, anomalies in these fictive error signals contribute to the diminished influence of potential consequences. Using a simple investment game and functional magnetic resonance imaging [fMRI] in chronic cigarette smokers, we measured neural and behavioral responses to error signals derived from actual experience and from fictive outcomes.”

They discovered: “In nonsmokers, both fictive and experiential error signals predicted subjects' choices and possessed distinct neural correlates. In chronic smokers, choices were not guided by error signals derived from what might have happened, despite ongoing and robust neural correlates of these fictive errors.”

Their conclusion provides important and useful information because: “These data provide human neuroimaging support for computational models of addiction and suggest the addition of fictive learning signals to reinforcement learning accounts of drug dependence.”

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