"EEMCDA Insights: Models of Addiction" PDF

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"Models of Addiction" PDF, pages 11-14; 18-20; 22-25; 27-28; and 34-40 (Reading below). All material on these pages will be covered in the quiz.

Addiction is a global problem that costs many millions of lives each year and causes untold suffering. It can involve ingesting licit and illicit psychoactive drugs (e.g. alcohol, nicotine, opioids, stimulants, steroids, prescription painkillers, sedatives or cannabis) or other kinds of activity (e.g. gambling, computer gaming). The science of addiction has advanced to a point at which it is timely to examine the wide range of underlying mechanisms that have been identified and assess what these imply for the development of a comprehensive strategy for combating the problem. This report reviews theories of addiction that have been proposed, with a view to generating an overarching framework or model that captures all the main elements. It then examines how this model can be applied in assessment, prevention and treatment. The main conclusions are given below. The analysis and conclusions in this report are offered as a framework for discussion. 

Definitions of addiction vary, but all involve the notion of repeated powerful motivation to engage in an activity with no survival value, acquired through experience with that activity, despite the harm or risk of harm it causes. Definitions of addiction include ‘a primary, chronic disease of brain reward, motivation, memory and related circuitry … reflected in the individual pursuing reward and/or relief by substance use and other behaviours’ (American Society of Addiction Medicine) and ‘a condition of being abnormally dependent on some habit, especially compulsive dependency on narcotic drugs’ (www.thefreedictionary.com). Although these definitions do capture important features of addiction, they either focus on just one aspect of it or use terms that cannot be interpreted clearly. Analysis suggests that the key features that definitions attempt to capture are that addiction involves repeated powerful motivation to engage in an activity; it is acquired through engaging in the activity; the activity does not involve innate programming because of its survival value; and there is significant potential for unintended harm. This need not be limited to substance use or abuse. 

Numerous mechanisms underlying addiction have been discovered, and these have spawned a multitude of models, each of which addresses a part of the problem. A large number of models of addiction describing these mechanisms have been proposed. The models are very heterogeneous and do not fall into a neat hierarchical classification. However, for heuristic purposes they can be classified in terms of whether they focus on individuals or populations. Those that focus on individuals can be grouped into (1) those that focus on what has been termed ‘automatic processing’ (associative learning, drives, inhibitory processes and imitation, none of which requires self-reflection and which can be investigated using studies with non-human animals) and (2) those that focus on reflective choice processes (conscious decisions to behave in a particular way after a comparison of the costs and benefits), whether ‘rational’ (involving reason and analysis) or ‘biased’ (subject to emotional or other processes that distort the decision-making process). Cutting across the automatic–reflective distinction are theories that (3) focus on different types of goal (positive reward, acquired need and pre-existing need). In addition, there are (4) integrative theories that combine elements of automatic and reflective choice models, (5) theories that focus on change processes and (6) biological theories that describe the neural mechanisms thought to be involved in addiction. Models that take a population perspective include (7) social network theories, (8) economic models, (9) what might be termed communication/marketing models and (10) ‘systems’ models. 

An overarching model of behaviour (the COM-B model, which recognises that behaviour arises out of capability, opportunity and motivation) can be usefully applied to understanding addiction. It is evident from the research literature that an integrated model merits consideration that can encompass the full range of concepts in the above models. This would ideally recognise both the intra- and extraindividual factors involved and the interactions among them. An overarching model of behaviour has been proposed that recognises that behaviour (B) arises from three necessary conditions: capability (C), opportunity (O) and motivation (M). Such a model could potentially address this need. The model would not be a replacement for specific theories but rather provide a framework in which they could be understood and applied. Under this COM-B model, addiction could be viewed in terms of the psychological and physical capabilities possessed by individuals (e.g. the capacity for self-regulation, the ability to learn from punishment, the ability to formulate and adhere to personal rules), opportunities afforded by the social and physical environment (e.g. social and environmental cues, availability of alternative sources of reward, financial costs of the activity) and the competing motivations operating at relevant moments (e.g. need for emotional blunting, need for belonging, anticipation of pleasure or satisfaction, anticipation of relief from craving, fear of disapproval). The motivations may be ‘reflective’ in the sense that they involve analysing the costs and benefits of a given course of action (e.g. the belief that an activity is ‘wrong’ or ‘harmful’) or ‘automatic’ in the sense that they involve drives, emotional processing and habits (e.g. an intense feeling of the need to engage in an activity). 

The PRIME theory of motivation may provide a useful framework for understanding the motivational aspects of addiction. It is an integrative model of motivation that describes how ‘reflective’ and ‘automatic’ processes interact to control our behaviour and how these can promote addiction and recovery. Motivation is an important component of the COM-B model and consists of all the brain processes that energise and direct behaviour. The PRIME theory of motivation integrates existing models including learning theory, decision theory, self-control theory, identity theory and drive theory. It provides a framework for understanding how capability, opportunity and motivation interact and how the system as a whole can become disordered, as in the case of addiction. 

It is useful to distinguish factors that influence (1) initial enactment of the behaviour, (2) development of addiction, (3) attempts at recovery or mitigation and (4) relapse; however, there is also some commonality. Different factors have been found to influence the four phases of the addiction life cycle. These factors vary across different cultural contexts and different individuals. There is also considerable overlap in the factors that influence the different phases. This means that certain interventions (e.g. population-level interventions to restrict access or increase the financial cost) can impact initiation, development, attempts at recovery from addiction and the success of those attempts. 

Population estimates of the prevalence of addiction based on diagnostic criteria present considerable challenges. Consideration should be given to estimates based on the numbers of people engaging in a particular activity that is known to have significant addictive potential at a level which, in a population, involves significant harm. The multifaceted nature of addiction and involvement of intra-individual and environmental factors limits the value in seeking to determine the prevalence of addictions per se in populations. The resulting figures will vary substantially in terms of the thresholds of harm and strength or chronicity of motivation to engage in the behaviours. For the purposes of assessing the extent of the problem and need for interventions for different types of addiction, an alternative approach (and the one most commonly used in practice) is to assess the number of people engaging in a behaviour which is known to have significant addictive potential at a level that, on average, will cause significant harm (e.g. the prevalence of any tobacco use or alcohol consumption above a risk threshold). Assessment of addiction in individuals and populations for the purposes of understanding and intervention could potentially involve all aspects of the COM-B system including capacity for self-regulation, environmental drivers, and wants and needs met by the addictive behaviour. 

A comprehensive framework for developing behaviour change interventions has been developed that could potentially be used to develop an intervention strategy for combating addiction. The COM-B model of behaviour has been linked to a system for developing an intervention strategy to achieve behaviour change. This identified a set of nine intervention functions (education, persuasion, incentivisation, coercion, training, restriction, environmental restructuring, modelling and enablement) and a system for selecting these on the basis of an analysis of what is driving the current behaviour and what is needed to achieve the new ‘behavioural target’. The initial selection of intervention functions then leads to identification of specific behaviour change techniques (BCTs) that deliver these functions and policies (e.g. legislation, fiscal measures, service provision, communication/marketing) that enable them. 

Different intervention strategies might be needed for different addictive behaviours, different populations and individuals and different contexts. For example, if there is only weak motivation to cease the activity because of lack of a true understanding of the harms, it may be sufficient to educate about those harms. In a situation in which an individual’s behaviour is strongly under the control of immediate environmental triggers, environmental restructuring interventions may be appropriate. If an addictive behaviour is being driven powerfully by the need to relieve or blunt emotional distress, then enabling interventions that provide an alternative source of relief may offer a solution. If an addiction is being driven largely by an acquired self-perpetuating drive arising out of the pharmacological actions of a drug, recovery may be promoted by alternative medications such as partial agonists. In general, however, a multifaceted approach that addresses the system as a whole is likely to be needed. 

Multiple addictions and co-morbidities can arise from mutually interacting processes within any part of the COM-B system. The presence of more than one type of addiction concurrently, and the combination of addiction and other psychological problems, can be viewed as arising from common aetiology in terms of capabilities, motivation and opportunities and from the way in which these interact with each other. For example, child abuse, leading to low self-esteem, can have multiple effects in terms of a lack of self-protective motives or even motives for self-harm as well as impaired skills for self-regulation, a need for relief from depression or anxiety and engagement with a subculture that provides opportunities for particular kinds of activity including use of particular licit or illicit drugs depending on social and other factors. From such a perspective, an important starting point for prevention and treatment would be to identify appropriate entry points into the COM-B system to achieve change that spreads throughout the system.

Chapter 1: Background, scope and aims 

1.1 The EMCDDA 

Illicit psychoactive drug use, excessive alcohol consumption, tobacco use and problem gambling create serious harm both to those individuals who engage in such practices and to society as a whole (World Health Organization, 2002). The European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) was established in 1993 to provide the European Union (EU) and its Member States with up-to-date information on European drug problems and a solid evidence base on which to develop policies to combat these. It also helps practitioners and researchers working in the field to identify best practice and fruitful avenues for future research. Although the EMCDDA is primarily European in focus, it also works with partners in other world regions, exchanging information and expertise. Collaboration with European and international organisations in the drugs field is also central to its work as a means of enhancing our understanding of the global drugs phenomenon. 

As part of its role in establishing the evidence base on drug problems, the EMCDDA is interested in developing a better understanding of the psychological and social causes of those problems. While it is clear that drug problems do not stem exclusively from addiction, addiction does play a major role. It is also apparent that addiction is a phenomenon that is not limited to illicit psychoactive drugs or, indeed, pharmacological agents. A number of European countries have established centres of addiction that potentially cover the full gamut of addictive behaviours. Therefore, the EMCDDA commissioned this report in order to provide a clearer understanding of the nature of addiction, the lessons that addiction to alcohol and tobacco and non-pharmacological addictions can provide for understanding addiction to illicit drugs and the extent to which understanding illicit drug addiction can shed light on other addictions. 

1.2 Scope 

The report reviews models specific to addiction as well as more general ones that have been widely used to help understand addiction. What constitutes a ‘model’ is interpreted quite broadly in order to encompass general theoretical approaches as well as specific theories. The terms ‘theory’ and ‘model’ are often used interchangeably, although in some cases one term is slightly more appropriate — a theory being a specification of a set of hypothetical causal connections between a set of elements or constructs and a model being a description of links between observable elements or constructs. Thus, theories are explanatory whereas models can be purely descriptive. 

The report does not examine detailed specific mechanisms relating to individual addictive behaviours, such as the role of the gamma-aminobutyric acid system in nicotine reward (Berrendero et al., 2010). Addiction and dependence are considered synonymous (see Table 2.1 on p. 22). Addictive behaviours that do not involve psychoactive drugs are included. 

This report covers some of the issues that are also the subject of ALICE RAP, a large European Community (EC)-funded project aimed at assessing the conceptualisation and assessment of addiction within the current European context (ALICE RAP Project, 2011). ALICE RAP involves a much more extensive series of investigations, but it is hoped that this report will help inform the project. 

1.3 Aims 

This report aims to: 

Following these aims, the EMCDDA wishes to support drug policy with a comprehensive definition and understanding of the term ‘addiction’, reflecting scientific developments and debates over recent years. This publication should help to answer the question not just of how far different types of addiction are similar in phenomenological and aetiological respects, but also of how we can target interventions to stop ‘addiction’ or at least limit its negative effects. 

This report will aim to broaden the views of this field, which has caused numerous problems in the past, by bringing together constructs that have been developed around illicit and licit substances, substance- and non-substance-related forms of behaviour and by making use of biological, sociological and psychological concepts.

Chapter 2: Defining addiction 

Before considering the range of models of addiction that have been proposed, it is necessary to define how the term will be used in this report. Addiction has been defined in different ways at different points in recent history and even now there are numerous partially overlapping definitions in the technical and general literature (see Table 2.1). This is because it is a multifaceted, socially defined construct rather than a physical entity with clear, uniquely defined boundaries. Some people and organisations prefer to avoid the term ‘addiction’ altogether because of pejorative connotations, while others make a distinction between ‘addiction’ and ‘dependence’. This report uses the term ‘addiction’ rather than dependence, but it incorporates into the term the features covered by major definitions of dependence. 

Table 2.1: Examples of definitions of addiction

Definition(source)	Comment
Addiction is a primary, chronic disease of brain reward, motivation, memory and related circuitry. Dysfunction in these circuits leads to characteristic biological, psychological, social and spiritual manifestations. This is reflected in the individual pursuing reward and/or relief by substance use and other behaviors. Addiction is characterized by impairment in behavioral control, craving, diminished recognition of significant problems with one’s behaviors and interpersonal relationships, and a dysfunctional emotional response. Like other chronic diseases, addiction often involves cycles of relapse and remission. Without treatment or engagement in recovery activities, addiction is progressive and can result in disability or premature death (American Society of Addiction Medicine)	This considers addiction as a brain disease, which implies that it requires treatment. It neglects environmental and social forces at play and the facts that it involves a continuum and that many individuals ‘recover’ without treatment
Compulsive physiological and psychological need for a habit-forming substance or the condition of being habitually or compulsively occupied with or involved in something (The American Heritage Dictionary, 4th edition)	Broadly based, but transfers the burden of interpretation onto words such as ‘compulsive’, ‘need’ and ‘habit’
A physical or psychological need for a habit-forming substance, such as a drug or alcohol. In physical addiction, the body adapts to the substance being used and gradually requires increased amounts to reproduce the effects originally produced by smaller doses. A habitual or compulsive involvement in an activity, such as gambling (The American Heritage Science Dictionary)	As above, but provides a clear definition of ‘physical’ addiction, which represents only a small part of the problem of addiction as it is currently construed
The condition of being abnormally dependent on some habit, esp[ecially] compulsive dependency on narcotic drugs (Collins English Dictionary)	Transfers the burden of interpretation onto ‘abnormal’ and ‘compulsive’
Addiction is a persistent, compulsive dependence on a behaviour or substance. The term has been partially replaced by the word dependence for substance abuse. Addiction has been extended, however, to include mood-altering behaviours or activities. Some researchers speak of two types of addictions: substance addictions (for example, alcoholism, drug abuse, and smoking); and process addictions (for example, gambling, spending, shopping, eating, and sexual activity). There is a growing recognition that many addicts, such as polydrug abusers, are addicted to more than one substance or process (Gale Encyclopaedia of Medicine)	Brings in the concept of persistence but transfers the burden of interpretation onto ‘compulsive’ and ‘dependence’
A compulsive, uncontrollable dependence on a chemical substance, habit, or practice to such a degree that either the means of obtaining or ceasing use may cause severe emotional, mental, or physiologic reactions (Mosby’s Medical Dictionary, 8th edition)	The use of the term ‘uncontrollable’ rules out cases in which an individual is struggling but is successfully (for the time being, at least) controlling the behaviour
(Substance dependence) A preoccupation with and compulsive use of a substance despite recurrent adverse consequences; addiction often involves a loss of control and increased tolerance, and may be associated with a biological predisposition to addiction. 1. A physiologic, physical, or psychological state of dependency on a substance — or pattern of compulsive use, which is characterised by tolerance, craving, and a withdrawal syndrome when intake of the substance is reduced or stopped; the most common addictions are to alcohol, caffeine, cocaine, heroin, marijuana, nicotine — the tobacco industry argues that nicotine’s addictive properties are unproven, amphetamines. 2. A disorder involving use of opioids wherein there is a loss of control, compulsive use, and continued use despite adverse social, physical, psychological, occupational, or economic consequences. 3. A neurobehavioral syndrome with genetic and environmental influences that results in psychological dependence on the use of substances for their psychic effects; addiction is characterised by compulsive use despite harm (McGraw-Hill Concise Dictionary of Modern Medicine)	Deals with only substance use and includes a set of features that, although common, are not always present
(Substance dependence) Repeated use of a psychoactive substance or substances, to the extent that the user (referred to as an addict) is periodically or chronically intoxicated, shows a compulsion to take the preferred substance (or substances), has great difficulty in voluntarily ceasing or modifying substance use, and exhibits determination to obtain psychoactive substances by almost any means. Typically, tolerance is prominent and a withdrawal syndrome frequently occurs when substance use is interrupted. The life of the addict may be dominated by substance use to the virtual exclusion of all other activities and responsibilities. The term addiction also conveys the sense that such substance use has a detrimental effect on society, as well as on the individual; when applied to the use of alcohol, it is equivalent to alcoholism. Addiction is a term of long-standing and variable usage. It is regarded by many as a discrete disease entity, a debilitating disorder rooted in the pharmacological effects of the drug, which is remorselessly progressive. From the 1920s to the 1960s attempts were made to differentiate between addiction and ‘habituation’, a less severe form of psychological adaptation. In the 1960s the World Health Organization recommended that both terms be abandoned in favour of dependence, which can exist in various degrees of severity. Addiction is not a diagnostic term in ICD-10, but continues to be very widely employed by professionals and the general public alike (World Health Organization Lexicon of Alcohol and Drug Terms)	Includes a detailed description of substance dependence including features that are not always present
(Substance dependence) When an individual persists in use of alcohol or other drugs despite problems related to use of the substance, substance dependence may be diagnosed. Compulsive and repetitive use may result in tolerance to the effect of the drug and withdrawal symptoms when use is reduced or stopped (Diagnostic and Statistical Manual of Mental Disorders, 4th edition)	Introduces the notion of continued use despite harmful effects

It is apparent that some definitions focus exclusively on drugs, yet it is clear that behaviours such as gambling can become problematic and dominate people’s lives. Some definitions refer to withdrawal symptoms even though these need not occur nor be a primary driver behind the compulsive behaviour. Some refer to the development of tolerance, again despite the fact that tolerance need not occur. Some focus on brain abnormality, even though individuals can clearly exhibit all the signs of addiction in one set of circumstances and yet, with the same brain, not in others. Loss of control, or impaired control, is another common theme, even though this would exclude the possibility of addiction where no attempt was being made to exert control. 

Definitions serve a purpose, so different definitions may be needed for different purposes. The key purpose of the definition used in this report is to provide a basis for describing and explaining repeated occurrence of behaviours that appear to be purposeful and not aimed at causing harm but from which harm typically ensues and where ignorance of this, or lack of concern about it, is not an adequate explanation. The explanation lies in a distortion of the individual’s motivational system and/or an environment that promotes the behaviour pattern. Such a broad definition is needed in order to develop a comprehensive intervention strategy to combat it. 

It is widely recognised that, for many people, the use of drugs such as alcohol, nicotine, heroin, cannabis, amphetamines, benzodiazepines and cocaine falls into this category (National Institute on Drug Abuse, 2011). It is also recognised that eating palatable foods, gambling, using the Internet, purchasing behaviour and sexual behaviours can also be addictive (Padwa and Cunningham, 2010).

Table 2.2: Scenarios to test definitions of addiction

An individual is addicted if he or she...

An individual is not addicted if he or she...

•  feels a need to take benzodiazepines every evening in order to sleep when, in fact, they do not help. •  is engaging in antisocial and personally harmful activities in order to be able to smoke crack cocaine. •  experiences powerful desires to smoke cannabis, which overwhelm prior decisions to desist. •  has his or her life dominated by using heroin and obtaining the money to buy heroin. •  develops a powerful need to drink alcohol in an escalating pattern of consumption. •  continues to engage in a behaviour to an extent that he or she recognises it as harmful despite having tried to stop. •  regularly experiences a powerful desire to engage in the behaviour. •  has not smoked cigarettes for 4 weeks but still experiences strong urges to smoke. •  does not smoke every day but has tried to stop smoking completely and failed several times. •  drinks alcohol in the mornings to relieve feelings of anxiety. •  has not drunk alcohol for 3 months but still gets strong cravings for it. •  spends hours each day gambling online and steals to cover the costs.

•  eats too much food high in saturated fats. •  feels a strong motivation to try alcohol but has not yet done so. •  does not feel a powerful desire to engage in the behaviour in situations when it would normally occur. •  takes medication every day to relieve chronic pain. •  has antisocial personality disorder, Tourette syndrome or obsessive– compulsive disorder without other behavioural problems. •  takes a psychoactive drug for the pleasurable experience but does not experience a powerful desire to take the drug when it is not available. •  gains satisfaction from an activity and self-consciously decides that the benefits outweigh the costs, and shares this analysis with society. •  drinks heavily but can easily go for several months without drinking. •  gambles heavily but not to a point where it is causing significant harm. •  is motivated to harm others.

Putting all of the above together, the definition of addiction adopted in this report is therefore as follows: 

Note that, unlike some existing definitions, this definition does not mention impaired control, conflict, need, withdrawal symptoms, craving or other putative mechanisms. The reason is that the definition has to be able to define the domain of interest but, as far as possible, avoid prejudging the underlying mechanisms, which may vary from case to case. The accumulated evidence indicates that impaired control, conflict, craving and so on are not necessary features of addiction even though they are frequently observed and have to be accounted for in any comprehensive theory.

Chapter 4: Modelling in the individual 

Addiction arises out of either pre-existing characteristics of individuals or the acquisition of characteristics that, together with a given set of environmental circumstances, result in powerful motivations to engage in harmful behaviour patterns. 

Prevention involves protecting individuals from factors that promote addiction. Recovery involves changing individuals or their circumstances to redress the motivational imbalance. 

Individual-level theories attempt to explain addiction by reference to concepts that apply to individuals and their circumstances. Individuals are regarded as possessing particular dispositions and/or inhabiting particular environments that promote addiction, through either initial engagement in the addictive activity or susceptibility to the development of addiction once the individual has undertaken the activity and been exposed to its consequences. Recovery from, improvement in or management of addiction involves changes to one or more of these. 

The main classes of theory can be differentiated in terms of those that focus on what are termed ‘automatic processes’, which do not involve self-conscious analysis of the options or reflective choice. Cutting across this are theories that emphasise positive reward seeking versus acquisition of needs, or the presence of pre-existing needs. Some models seek to integrate these different approaches to different degrees. These include self-control theories (which reflect conflict between reflective and automatic processes) and broader integrative theories. There are also theories that focus exclusively on change processes. The above theories are usually framed at the psychological, sociological or economic level of analysis, but there are numerous theories that are framed at the biological level as well. Many of these theories cut across the categories indicated above, so they are addressed separately in this report. 

4.1 Automatic processing theories 

Addicts acquire addictive behaviours through mechanisms that shape human behaviours without the need for conscious decisions or intentions and/or influence our capacity for self-regulation. 

Prevention and promotion of recovery involve changing the environment to alter exposure to cues and/or reinforcers, cueing and reinforcing competing behaviours and/or improving the efficiency of inhibitory mechanisms. 

4.1.1 Learning theories 

Learning theories derive from studies, mainly in non-human species, in which behaviour can be shaped by applying rewarding or noxious stimuli. This area of theory is extremely well developed and has been applied to humans as a way of explaining a wide range of behaviours (Mook, 1995). This body of theory differs from theories of reflective choice in that the processes involved do not need to result in self-conscious decisions. The rat is presumed not to think to itself, ‘If I press this lever I will receive some food; I am hungry and I want food; therefore I will press this lever.’ The rat may experience pleasure or pain in some sense and that may be important in the learning process, but it does not reflect on that experience and use that information in an analysis of the pros and cons of lever pressing. 

When learning theory is applied to humans, the presumption is that we have retained the brain mechanisms that lead a rat to learn to press a lever for food or avoid an electric shock. Furthermore, these mechanisms continue to shape our behaviour. Therefore, the positive experiences, or avoidance of or escape from negative experiences, afforded by addictive behaviours drive behaviour through the creation of motivational states (e.g. wanting, needing, craving, urges, impulses, etc.) that are not reflective or based on reflective analysis. 

Addiction arises because certain activities are powerfully rewarding and become more so through exposure. 

Theory 

Addiction involves learning associations between cues, responses and powerful positive or negative reinforcers (pleasant or noxious stimuli). 

Evidence 

•  Non-human species can acquire addictive behaviour patterns through repeated pairing of cues, responses and reinforcers (Ahmed, 2011). 

•  At least some human addictive behaviours appear to show acquisition and extinction patterns predicted by operant and classical conditioning theory — see below for examples of learning theory (Hyman et al., 2006). 

•  At least some addictive behaviours appear to involve automatic habit mechanisms (Tiffany, 1990). 

Limitations 

•  This kind of theory does not account for the role of self-conscious intentions, desires or beliefs that have not been acquired through experience (Vuchinich and Heather, 2003). 

•  Treatments aimed at promoting recovery using cue-exposure techniques have not proved successful to date (Conklin and Tiffany, 2002), although promising lines of research continue (Kaplan et al., 2011). 

Examples 

Operant learning theory (operant conditioning): This is a general theory of behaviour change in which, in the presence of particular cues, experience of positive and negative ‘reinforcers’ increases or decreases the likelihood of occurrence of a behaviour on which it is contingent (Mook, 1995). Positive reinforcers are events that increase the frequency of prior behaviours, whereas negative reinforcers are events that decrease that frequency or which will lead to behaviours that achieve avoidance or escape from them. Operant conditioning is a very widely studied subject and probably the single most powerful body of theory in motivational psychology. The paragraphs that follow provide only a very broad overview. 

A trainer might get a dog to stand on its hind legs at his or her command by giving it highly palatable food for doing so. The tasty food is a positive reinforcer. The process is ‘automatic’ in the sense that the dog is presumed not to self-consciously decide to rear up because it weighs up the costs and benefits of doing so; rather, the command acts as a stimulus that triggers the ‘image’ of the food, which leads to anticipated ‘pleasure’ (although the dog would not be able to reflect on this emotion), which in turn triggers the behaviour. 

Negative reinforcement involves inducing behaviour which terminates or avoids an aversive stimulus. Thus, most animals will readily learn to respond in order to avoid electric shocks as long as it is made clear by means of some kind of signal that the shock will be delivered if the animal does not respond. This is known as ‘signalled avoidance’ learning. Unsurprisingly, it is much harder for animals to learn to avoid aversive stimuli when no signal is given (‘unsignalled avoidance’); in such situations, the animal will often develop ‘learned helplessness’ (Seligman, 1972), in which it simply takes the aversive stimulus and makes no attempt to avoid it. ‘Escape learning’ is the term given to a situation in which an animal learns to engage in a particular action in order to terminate or reduce an aversive experience. 

Punishment is the term used when the frequency of a behaviour is reduced because it is followed by an aversive stimulus or termination of a positive stimulus. Table 4.1 shows the major terms used in operant learning theory. For a more detailed description see Mook (1995). 

Table 4.1: Major terms in operant learning theory

Type of reinforcement contingency	Description	Example
Positives reinforcement	A neural adaptation which increases the likelihood of a response to a given cue when, in response to the cue, a behaviour is followed by a positive reinforcer or reward	At a party the positive experience following nasal ingestion of cocaine increases the likelihood that this activity will be repeated in similar situations in the future
Negative reinforcement	A neural adaptation which increases the likelihood of a response which leads to avoidance of, or escape from, a negative reinforcer or aversive stimulus	Heroin addicts learn to seek out and ingest heroin to avoid or escape from aversive heroin withdrawal symptoms
Punishment	A process in which a behaviour becomes less likely to occur as a result of it being followed by an aversive stimulus or termination of a positive stimulus	For some teenagers, the coughing, nausea and other symptoms experienced when they first try to inhale cigarette smoke deters them from doing it again
Extinction	A process whereby, when a response that was maintained by a positive reinforcer is no longer followed by a reinforcer, its likelihood of occurrence is reduced	Pharmacological blockade of the opiate receptors by naxolone can decrease the rate of heroin injecting

      

Some major discoveries in operant learning theory have provided important insights into addictive behaviours. For example, it has been found that when a positive reinforcer is applied intermittently and unpredictably it can lead to very high rates of response that are resistant to extinction. This is known as a ‘variable ratio schedule of reinforcement’. Gaming machines make use of this principle by timing the quantity and frequency of delivery of payouts (Haw, 2008). 

Classic (Pavlovian) conditioning theory: Classic and operant conditioning are very closely connected. Both involve associative learning. While operant conditioning involves forming associations between cues and responses involving the so-called ‘voluntary muscles’ through the experience of reinforcement, in classic conditioning the association is formed between stimuli and feeling states or reflex responses by virtue of the stimuli being immediately predictive of other motivationally or emotionally significant stimuli (Mook, 1995). 

Thus, in classic conditioning, stimuli that would normally be only weakly motivating at best can come to have motivational power by being associated with more powerful reinforcers. This can lead to an addictive behaviour becoming more powerfully established than it would have done otherwise. For example, the sensation of smoke in the throat and the sight and tactile sensations associated with smoking acquire reinforcing properties by virtue of being associated with the rewarding actions of nicotine. This establishes the whole behaviour chain involved in smoking more powerfully than would be the case were it to rely on only the nicotine reward. 

This is a highly developed area of theory and important nuances have emerged. For example, a distinction has been drawn between associative learning, in which liking and disliking a stimulus is influenced by associations between that stimulus and liked and disliked stimuli (termed ‘evaluative conditioning’), and traditional classic conditioning, in which a stimulus that predicts a motivationally significant stimulus acquires a response that anticipates it; for example, a stimulus that predicts a pleasurable stimulus may come to generate excitement (Hofmann et al., 2010). There is also discussion about whether, or in what circumstances, people need to be aware of (or able to articulate) a contingency between two stimuli for conditioning to occur (Olsen and Fazio, 2002; Pleyers et al., 2007). There is a body of evidence that suggests that, even if awareness is not essential, it is probably facilitatory (Bar-Anan et al., 2010). 

Incentive-sensitisation theory: Variants of this theory have become dominant in the biological models of addiction or contributed significantly to more integrative biological models (see point 4.5, pp. 70-73). This theory proposes that repeated self-administration of addictive drugs leads to neuroadaptation in which the behaviour becomes less and less under the control of anticipated pleasure (‘liking’) and more under the control of ‘incentive salience’, the subjective manifestation of which is ‘wanting’ (Robinson and Berridge, 2001). Thus, in the development of addiction, a dissociation can be observed between ‘wanting’ and ‘liking’ (Berridge et al., 2009). 

Behavioural momentum and inertia theory: According to this theory, the relation between response rates and resistance to change is akin to the velocity and mass of a moving object. The momentum of a behaviour, which is its tendency to continue in the absence of reinforcement or when already satiated, is proposed to reflect the strength of stimulus–reinforcer associations rather than response– reinforcer associations (Nevin and Grace, 2000). This means that contexts in which an addictive behaviour occurs may play a greater role in maintaining the behaviour than would be expected from classical operant conditioning models. This theory is relatively new but has been applied to research into both cocaine (Quick and Shahan, 2009) and alcohol addiction (Jimenez-Gomez and Shahan, 2007). 

Implications for prevention and promoting recovery 

The main implications of learning theory approaches are that prevention of addictive behaviours must focus on removing the opportunities for potential addicts to become exposed to the behaviours, and treatment should involve attempting to loosen the associations between cues and rewards or cues and behaviour. For example, one might use ‘cue exposure’ to loosen the association between reward and the behaviour or medications that block the reinforcing actions of the addictive drug (antagonists) (Ferguson and Shiffman, 2009). 

4.1.2 Drive theories 

Drive theories invoke the concept of homeostatic mechanisms that seek to keep certain physiological parameters within specified limits (Mook, 1995). In drive theory, automatic processes result in heightened motivational states that energise and direct behaviours that reduce those states. Once homeostasis is reached, there is satiation and no need for further activity. Addictive behaviours are those that reduce drive states — whether these are artificially induced by the behaviour or through other means. 

Theory 

Addiction involves the development of powerful drives underpinned by homeostatic mechanisms. 

Evidence 

•  Many addictive behaviours appear to follow temporal patterns suggestive of drive states, for example abstinence-induced desire, ‘kindling’ and satiation (Kostowski, 2002). 

•  Many addictive behaviours influence, and are influenced by, naturally occurring drive states, for example hunger (Kokavec, 2008; Yeomans, 2010).

•  Subjective reports of urges to engage in many addictive behaviours have characteristics similar to naturally occurring drive states (Shiffman, 2000). 

•  Physiological and neuroanatomical evidence suggests that central nervous system (CNS) changes would lead to acquisition of abnormal homeostatic processes, for example chronic receptor upregulation (Koob, 2008). 

Limitations 

•  Not all addictions appear to follow a pattern suggestive of need for homeostasis, and even addictions that suggest a homeostatic drive mechanism also show evidence of other important influences (Koob and Le Moal, 2008). 

Examples 

The ‘disease model’ of addiction: This model is general and has many features that go beyond drive theory, but at its heart is the idea that addiction involves pathological changes in the brain that result in overpowering urges to engage in the addictive behaviour. This model has been very influential in ‘medicalising’ addiction because it construes it as a medical disorder — an abnormality of structure or function that results in impairment (Gelkopf et al., 2002). The addicted individual may express a sincere desire to stop the addictive behaviour and show evidence of making strenuous efforts to do so while at the very same time carrying on with it.

The loss of control may be manifest over short and long time spans. Over a period of a few hours, an alcoholic may begin a drinking session with the intention of having one or two drinks, but finds that it is impossible to stop and more and more drinks are consumed: the power to resist has gone. Over a longer time span, the alcoholic, smoker, gambler or other addict may formulate a plan not to engage in the activity, but after a time does in fact engage in it. The addict chooses to do one thing but repeatedly fails to put that intention into effect. 

At the heart of this theory is the concept of ‘craving’. In the disease model this has been defined as an ‘urgent and overpowering desire’ (Jellinek, 1960). One way of thinking about this is as a feeling that impels the addict to take whatever steps are necessary to achieve the object of the addiction. It can also be construed as a motivational state that goes beyond feelings: it overwhelms the individual, dominating his or her thoughts, feelings and actions to the exclusion of everything else. 

The serotonin theory of nicotine addiction: This theory arose out of the observation that many of the symptoms of nicotine withdrawal (increased appetite for carbohydrates, depressed mood and aggression) appeared similar to those of low serotonin concentrations in the CNS (Hughes, 2007). It was also noted that smokers often reported their cravings for cigarettes as feeling like hunger, which raised the possibility that they might — at least in part — reflect a physiological drive state very similar to that of hunger. It came to be labelled as craving because smoking a cigarette relieved it. This led to the theory that craving for a cigarette and some other nicotine withdrawal symptoms arose from serotonin depletion in key parts of the CNS, which leads to an acquired drive state of ‘nicotine hunger’ (Balfour, 2004; West, 2009). This depletion was proposed to result from disruption of the regulation of serotonin pathways resulting from long-term nicotine use. 

Control systems dynamical model of smoking urges: One of the problems with classic drive theory accounts is their failure to take account of the highly dynamic and fluid nature of drives. A recent theory, which uses concepts from fluid mechanics to model the strength of ‘smoking urge’ in a time-variant manner, has sought to address this issue (Riley et al., 2011). ‘Sensors’ monitor negative affect (e.g. depression, anger) and other variables such as medication, exercise, positive affect and smoking behaviour. These and a system of ‘valves’, which adjust the weighting applied to each variable to measure on a moment-to-moment basis, define the strength of urges. These in turn control the decision to smoke

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