R J Lamb1, Charles W Schindler2, Jonathan W Pinkston3. 1. Departments of Psychiatry & Pharmacology, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX, 78229-3900, USA. lamb@uthscsa.edu. 2. Preclinical Pharmacology Section, Behavioral Neuroscience Research Branch, Intramural Research Program, National Institute on Drug Abuse, 251 Bayview Blvd, Baltimore, MD, 21224, USA. 3. Department of Behavioral Analysis, University of North Texas, 360 G Chilton Hall, Avenue C, Denton, TX, 76208, USA.
Abstract
RATIONALE AND OBJECTIVE: Pavlovian learning is central to many theories of addiction. In these theories, stimuli paired with drug ingestion become conditioned stimuli (CS) and subsequently elicit drug-seeking and drug-taking. However, in most relevant studies, Pavlovian and instrumental learning are confounded. This confound may be avoided in Pavlovian-Instrumental-Transfer (PIT) procedures. In PIT, Pavlovian and instrumental learning are established separately and then combined. In order to better understand the role of CSs in addiction, we review the relevant studies using PIT. FINDINGS: We identified seven articles examining PIT effects of ethanol- or cocaine-paired CSs. Under at least one condition, six of these articles reported CS-elicited increases in responding previously maintained by drug. However, the only study using the optimal control condition failed to find a CS-elicited increase. Two studies examining CS specificity found the CS also increased responding maintained by a different reinforcer. Two studies examined if CSs elicit increases in actual drug-taking. Both failed to find CS-elicited increases, i.e., no study shows CS-elicited increases in actual drug-taking. Further, CS-elicited increases in extinguished responding are short-lived. CONCLUSIONS: These findings are not entirely consistent with Pavlovian learning playing a central role in addiction. However, design issues can explain most of these inconsistencies. Studies without these design issues are needed. Additionally, existing theories hypothesize drug-paired CSs increase drug-taking by increasing motivation, by eliciting conditioned responses that make drug-seeking more probable, or by a combination of these. Work distinguishing between these mechanisms would also be useful.
RATIONALE AND OBJECTIVE: Pavlovian learning is central to many theories of addiction. In these theories, stimuli paired with drug ingestion become conditioned stimuli (CS) and subsequently elicit drug-seeking and drug-taking. However, in most relevant studies, Pavlovian and instrumental learning are confounded. This confound may be avoided in Pavlovian-Instrumental-Transfer (PIT) procedures. In PIT, Pavlovian and instrumental learning are established separately and then combined. In order to better understand the role of CSs in addiction, we review the relevant studies using PIT. FINDINGS: We identified seven articles examining PIT effects of ethanol- or cocaine-paired CSs. Under at least one condition, six of these articles reported CS-elicited increases in responding previously maintained by drug. However, the only study using the optimal control condition failed to find a CS-elicited increase. Two studies examining CS specificity found the CS also increased responding maintained by a different reinforcer. Two studies examined if CSs elicit increases in actual drug-taking. Both failed to find CS-elicited increases, i.e., no study shows CS-elicited increases in actual drug-taking. Further, CS-elicited increases in extinguished responding are short-lived. CONCLUSIONS: These findings are not entirely consistent with Pavlovian learning playing a central role in addiction. However, design issues can explain most of these inconsistencies. Studies without these design issues are needed. Additionally, existing theories hypothesize drug-paired CSs increase drug-taking by increasing motivation, by eliciting conditioned responses that make drug-seeking more probable, or by a combination of these. Work distinguishing between these mechanisms would also be useful.
Authors: Hans S Crombag; Jennifer M Bossert; Eisuke Koya; Yavin Shaham Journal: Philos Trans R Soc Lond B Biol Sci Date: 2008-10-12 Impact factor: 6.237
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