A study published in the Journal of Neuroscience (behind a paywall here, but see also a media report here a a few days ago suggests that cocaine addicts may have impairments in the neural circuits that are responsible for the prediction of emotional loss. In this post, I shall consider the implications that this finding might have for our understanding of addiction and the autonomy of addicted individuals.
A Summary of the Study
The study set out to measure dopaminergic Reward Prediction Error (RPE) in addicted individuals compared to healthy subjects. RPE signals are commonly understood to reflect a discrepancy between a predicted and an actual rewarding outcome; these signals are then used to update the expected value of the stimulus that led to the rewarding outcome. As such, RPE is often deemed to be central to human learning; after performing some act (or experiencing some stimulus), the extent to which we will seek to repeat or avoid that behaviour in future will depend, it is claimed, on whether our previous experience led to an increase in dopaminergic signalling (i.e. if we experienced an unpredicted reward), or a decrease (i.e. if we experience a negative outcome, or the omission of an expected positive reward).
Briefly, the experiment in the recent study involved subjects playing a gambling game in which they would predict whether they would win or lose money in each individual trial, given one of three known win probabilities (25%, 50%, or 75% chance). Whilst playing the game, subjects were monitored using Electroencephalography (EEG), allowing researchers to record electrical activity in the subject’s brain.
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