Does ‘unlearning’ ever really occur: comment on Conklin & Tiffany

Sir—In a previous issue of Addiction, Conklin & Tiffany (2002) presented a compelling argument to re-examine learning principles governing extinction of conditioned responses as a means to extinguish reactions to drug use-conditioned cues, which might provoke relapse to substance use. The authors present a meta-analysis of treatment studies which have used cue exposure methods to forestall relapse, but even this quantitative analysis is not needed to conclude that the methods used to date have failed, miserably. An informed tour through the recent literature on extinction paradigms in animals yields some insights into what forms and structures extinction trials may need to adopt if real extinction of conditioned responding is to be achieved. However, the authors make an exceedingly important point in noting that the bond between conditional stimulus and conditioned response may in fact remain indelible. Thus, extinction, conceived as ‘unlearning’, may never really occur. Studies of the neural basis of learned fear and defensive responding confirms this possibility (LaBar et al. 2001). Extrapolating from conditioning of aversive stimuli to appetitive stimuli, we may never be able to extinguish appetitive responding to drug use cues. Nevertheless, individuals ‘learn’ to cope with cue-induced craving, perhaps in a number of ways—cognitively, by avoiding or suppressing conditioned craving responses, and behaviorally, by suppressing drug-seeking actions, physically fleeing or avoiding situations where drug use cues are present, or by engaging in alternative, drug-free behaviors. Inhibition of conditioned fear responding is controlled to a large extent by higher cortical structures, and the same is probably true of conditioned appetitive responding. Herein lies what I believe to be the real promise of cue exposure therapies. Higher order learning must take place in order to control highly automated conditioned reactions and drug-seeking behaviors in response to drug cues. Coping skills training to prevent relapse is designed to do just this. However, coping skills training may miss the mark if it is not practised, especially in the cue-laden contexts where drug craving is experienced and drug use occurs (Rankin et al. 1983). To be sure, there are enormous practical challenges in undertaking such in vivo coping/exposure therapy. As yet, there is no indication that cognitive-imaginal methods for evoking cue reactivity are sufficiently powerful to mimic exposure to real-world drug cues (Niaura et al. 1999). Perhaps media-rich technologies, such as virtual simulations of drug-using environments, will be helpful in this regard. We must heed Conklin & Tiffany’s advice on how best to configure cue exposure trials, and learn to combine this with coping skills training and practice, if the promise of cue exposure treatment is to be realized.