In the first of a three part series of blogs we discuss “what is craving?” and consider whether the emotional dysregulation we consider to be at the heart of alcoholism and addiction also plays a role in both craving and relapse.
We start this series by considering the neurobiological accounts of craving and will then consider how well these accounts explain craving and relapse in abstinent, treatment seeking, or recovering alcoholics and addicts.
What is craving?
Craving persists years into abstinence (1). Precise definitions of craving have remained elusive (2-5). Two general categories are based on conditioning and cognitive mechanisms (6) but are not mutually exclusive.
A Neuroadaptive Model of Craving – Scientists believe that a gradual and, perhaps, permanent adaptation of brain function (i.e., neuroadaptation) to the presence of alcohol is a central feature in the development of alcohol dependence (7,8).
Conditioning Models – The “conditioning” models posit that cues elicit the same physiological and psychological response as drug consumption itself with these ‘respondent’ conditioning theories predicting that responses to drug-related cues either reflect aversive abstinence symptoms or mimic drug effects have dominated explanatory models in cue reactivity studies (9).
The definition of addiction by the American Society of Addiction Medicine (ASAM) includes the terms craving and persistent risk, and emphasises risk of relapse after periods of abstinence triggered by exposure to substance-related cues and emotional stressors (10). This conceptualisation points to the role of substance-related cues, e.g., environmental stimuli that are strongly associated with the effects of the administration of substances and acquire incentive salience through Pavlovian conditioning, as well as stress (an internal cue), as major determinants of relapse.
The Incentive Sensitisation (IS) Model (11), addiction is the result of neural sensitisation of reward circuits (centred in the ventral striatum (VS)) by the neurotransmitter dopamine. Positive reinforcement mechanisms lead to a non-associative learning process, referred to as sensitization, in which repeated confrontation with a substance-related cue (which acts as a reinforcer) results in the progressive amplification of a response (substance seeking).
This ‘sensitisation’ or hypersensitivity may be independent of negative withdrawal symptoms or an individual’s general negative emotional state and leads to compulsive substance-seeking and substance-taking. These mechanisms of positive reinforcement leave addicts vulnerable to relapse when confronted with substance-related cues that trigger a pathological “wanting”. In short, IS produces a bias of attentional processing towards substance-associated stimuli and a pathological wanting of alcohol or substances. Sensitisation and attentional bias have been demonstrated in various studies (12,13).
Negative reinforcement model of addiction Basic negative reinforcement models pose that addictive behaviour is the consequence of persistent negative affect (NA). This NA is associated with maladaptive changes in the brain’s stress and reward circuits, which leave addicts vulnerable to cue-associated stimuli prompting a desire to relieve their negative emotional states (14).
One prominent stress-based negative reinforcement model, the Hedonic Dysregulation (HD) Model, mainly associated with Koob and le Moal (14), In sum, the HD model posits that, in substance dependent individuals, an overactive HPA axis creates a progressive allostasis in the brain reward systems which underlies transition from substance use to addiction and creates a persistent state of NA and emotional reaction to “cues”. These changes continue to persist even when an addicted individual experiences a state of protracted abstinence.
“Cues” that normally elicit substance-seeking behaviour are conceived as having greater impact during such periods of protracted abstinence. Persistent NA increases their incentive salience and desire to use substances in an attempt to relieve this NA.
Evidence for the involvement of both the reward and the stress system of the brain comes from imaging studies of addicted individuals during withdrawal or protracted abstinence, which have shown decreases in dopamine D2 receptor density (hypothesized to reflect hypodopaminergic function) (15) as well as alteration in brain stress systems, such as increase in CRF and glucocorticoids (16).
References 1. Anton, R. F. (1999). What is craving. Alcohol Research and Health, 23(3), 165-173.
2. LUDWIG, A.M., AND STARK, L.H. Alcohol craving: Subjective and situational aspects. Quarterly Journal of Studies on Alcohol 35:899–905, 1974.
3. KOZLOWSKI, L.T., AND WILKINSON, D.A. Use and misuse of the concept of craving by alcohol, tobacco, and drug researchers. British Journal of Medicine 82:31–45, 1987.
4. KOZLOWSKI, L.T.; MANN, R.E.; WILKINSON, D.A.; AND POULOS, C.X. “Cravings” are ambiguous: Ask about urges and desires. Addictive Behaviors 14:443–445, 1989
5. SITHARTHAN, T.; MCGRATH, D.; SITHARTHAN, G.; AND SAUNDERS, J.B. Meaning of craving in research on addiction. Psychological Reports 71:823–826, 1992.
6. SINGLETON, E.G., AND GORELICK, D.A. Mechanisms of alcohol craving and their clinical implications. In: Galanter, M., ed. Recent Developments in Alcoholism: Volume 14. The Consequences of Alcoholism. New York: Plenum Press, 1998. pp. 177–195.
7. Robinson, T.E., & Berridge, K.C. (1993). The neural basis of drug craving: An incentive-sensitization theory of addiction. Brain Research, 18, 247-291
8. Koob GF, Le Moal M. Drug abuse: hedonic homeostatic dysregulation. Science. 1997;278:52–58
9. Ingjaldsson, J. T., Laberg, J. C., & Thayer, J. F. (2003). Reduced heart rate variability in chronic alcohol abuse: relationship with negative mood, chronic thought suppression, and compulsive drinking. Biological Psychiatry, 54(12), 1427-1436.
10. Morse RM, Flavin DK (1992). “The definition of alcoholism. The Joint Committee of the National Council on Alcoholism and Drug Dependence and the American Society of Addiction Medicine to Study the Definition and Criteria for the Diagnosis of Alcoholism“. JAMA 268 (8): 1012–4
11. Robinson, T. E., & Berridge, K. C. (2008). The incentive sensitization theory of addiction: some current issues. Philosophical Transactions of the Royal Society B: Biological Sciences, 363(1507), 3137-3146
12. Leyton M. Conditioned and sensitized responses to stimulant drugs in humans. Prog. Neuropsychopharmacol. Biol. Psychiatry. 2007;31:1601–1613.
13. Franken, I. H. (2003). Drug craving and addiction: integrating psychological and neuropsychopharmacological approaches. Progress in Neuro-Psychopharmacology and Biological Psychiatry, 27(4), 563-579
14. Koob, G. F., & LeMoal, M. (2001). Drug addiction, dysregulation of reward, and allostasis. Neuropsychopharmacology, 24, 97–129.
15. Volkow ND, Wang GJ, Fowler JS, et al. Decreased striatal dopaminergic responsiveness in detoxified cocaine-dependent subjects. Nature. 1997;386:830–3. 16.. Koob GF, Le Moal M. Addiction and the brain antireward system. Annu Rev Psychol. 2008;59:29–53