Developing general models and theories of addiction - Nfap
Developing general models and theories of addiction
Robert West Department of Behavioural Science and Health, University College London
robertwest100@
Simon Christmas Independent consultant simon@
Janna Hastings Babraham Institute, University of Cambridge
janna.hastings@babraham.ac.uk
Susan Michie Centre for Behaviour Change, University College London
s.michie@ucl.ac.uk
Introduction
The science of addiction is being hampered by confusion in concepts and terms, and a multiplicity of models and theoretical approaches that make little reference to each other. In this respect it has much in common with other areas of social, clinical and behavioural sciences. Technologies now exist and are being rapidly advanced that can address this problem, and other sciences are already making use of them. In particular, what are known as `ontologies' (as used in computer science) and the `Semantic Web' could revolutionise our ability to formulate models and theories in addiction which can then provide much needed direction to the scientific endeavour.
The field of biology suffered from a similar problem until the development of what is known as the Gene Ontology (Ashburner et al., 2000). The gene ontology is not just about genes, but is a representational system for the whole of biology, unifying terms, definitions and models across species and research groups in a way that has revolutionised the field (Lewis, 2017).
This chapter introduces readers to ontologies and the semantic web, and explores their potential use in developing and expressing models and theories of addiction in ways that allow relationships to be examined between them, and between these and more general models and theories in clinical,
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population and behavioural sciences. These technologies also allow investigation of construct relationships within models, necessary for testing and hence refining and advancing them.
We begin by describing a central challenge facing the study of addiction: the need to achieve clarity of constructs and develop consensus while at the same time recognising that divergent views have utility. We then move on to describe some key characteristics of the Semantic Web, and the ways in which these provide a pragmatic way of responding to this challenge. We conclude by looking at the potential value of existing ontologies in developing a general theory of addiction.
The challenge: clarity and diversity
Models of addiction are necessary for building addiction science and developing effective interventions to combat this problem. If they go beyond describing observed relationships (descriptive models such as tobacco price elasticity (Gallus, Schiaffino, La Vecchia, Townsend, & Fernandez, 2006)) and attempt to explain phenomena we refer to them as `theories' (e.g. the dopamine theory of drug reward (Blum et al., 2015)). There are a plethora of models and theories of addiction differing in scope, emphasis, constructs and propositions but they have not been expressed in ways that allow them to be compared, tested or integrated.
The term `addiction' is itself an example of this lack of clarity in relation to key constructs. Many cases of psychoactive drug use have features that lead to the users being labelled as suffering from a condition called `addiction'. Sets of such features have been listed in `diagnostic criteria', such as DSM-5 (American Psychiatric Association, 2013) and ICD-10 (World Health Organisation, 2016). These include continued use despite harmful consequences, experience of adverse withdrawal symptoms during periods of non-use, difficulties controlling use, high levels of use, and repeated strong motivation to use. Features can be present to different degrees, which means that thresholds are required for deciding whether or not a pattern of drug use is addictive. These thresholds are to a large extent arbitrary and context dependent. An alternative, rather than considering addiction to be present or absent depending on whether some threshold is exceeded, is to assess the degree to which the features are evident to specify a `degree' of addictedness or `severity' of addiction (Gossop et al., 1995).
With multiple features potentially being involved, different ways of characterising these features, and different thresholds potentially being applicable, there can be substantial differences of view in whether an individual's pattern of drug use is considered addictive, or the degree of addictedness. These differences mean that issues such as the prevalence of addictions and theories concerning the causes of addiction are subject to differing viewpoints that cannot be reconciled solely by reference to objectively determined facts.
The picture is further complicated by the fact that different psychoactive drugs have different patterns of use and show different degrees and patterns of addictive features, as do different ways of using the same drug. An additional complication is that behaviours that do not involve psychoactive drugs, such as gambling, can show similar characteristics to drug addiction and so the concept of addiction appears to apply to those behaviours as well.
A similar lack of clarity exists for many other constructs which are important to a scientific understanding of addiction. Any general model or theory of addiction would need to capture processes that have been identified as important in its development and maintenance (Orford, 2001; West & Brown, 2013) (Table 1). Although conceptually different, many of these processes have features in common, or else the distinction between them is nuanced. For example, incentive sensitisation and drive theory both involve craving. In the case of incentive sensitisation, cravings are
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generated in response to cues through repeated exposure enhancing a direct link between those cues and the experience of `wanting' whereas drive theory proposes that cravings are generated through exposure to a drug leading to a state that is relieved by taking the drug. Some models and theories are fundamentally neurophysiological whereas others focus on social processes.
Table 1: Processes commonly included in models of addiction (West, 2017)
Processes
Description
Propositions in existing models
Cost-benefit
The benefits of the addictive
At least some people addicted to
analysis
behaviour are judged by the addict to alcohol believe that the benefits
outweigh the costs
in terms of anxiety relief and
mental escape are worth the
financial, social and health costs
Incentive
Repeated exposure to addictive drugs Smoking crack cocaine leads to
sensitisation
leads to sensitisation of brain
feelings of craving in situations
pathways that generate feelings of
similar to those where this has
`wanting' in response to drug cues
occurred, independent of feelings
independent of feelings of `liking'
of euphoria produced by the drug
Reward seeking
Addicts learn that addictive behaviours Methamphetamine users seek
provide positive feelings of enjoyment the `rush' provided by the drug
and euphoria
Attachment
Addicts become emotionally attached Smokers often report feeling a
to drugs or addictive behaviours
sense of bereavement during the
because these have been reliable
early stages of stopping smoking:
sources of comfort or gratification
like they have lost a cherished
friend or family member
Drive reduction
Repeated engagement in an addictive Repeated use of nicotine alters
behaviour results in development of brain physiology so that
an acquired drive, which is
abstinence results in an acquired
experienced as craving, after a period drive state, experienced as
of abstinence.
craving
Distress avoidance Addicts learn that addictive behaviours Repeated use of heroin results in
relieve mental and physical distress changes in brain chemistry
caused by mental health problems, life leading to adverse mood and
circumstances, and/or withdrawal
physical symptoms when
symptoms
concentrations of the drug fall
below certain concentrations in
the brain
Social influence
Cultural, sub-cultural, peer group
Family and peer group are
and/or family norms promote or are important factors influencing the
permissive of addictive behaviour
development of smoking and
alcohol consumption
Impaired control
Addictive behaviours develop, and are Use of stimulant drugs leads to
maintained by, pre-existing or
impairment in frontal lobe
acquired inefficiencies in brain
functioning required to inhibit
systems required for impulse control impulses to continually repeat
the use leading to bingeing
Classical
Repeated pairing of stimuli (cues)
Lights, images and sounds are
conditioning
associated with effects of addictive
used by gaming machine
behaviours leads those stimuli to
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Operant conditioning
generate anticipatory reactions to those effects Addictive behaviour are followed by powerful positive or negative reinforcers (rewards or offset of aversive stimuli) in the presence of discriminative stimuli (cues), so that those stimuli come to provoke a strong impulse to engage in the behaviour
manufacturers to promote high rates of use of those machines Use of psycho-stimulants is maintained by the positive reinforcing properties of these drugs
None of the processes believed to underlie addiction are limited to addictive behaviours; they are all involved in the development of other motivations (West & Brown, 2013). What makes a behaviour pattern addictive is the strength of the motivational forces generated and/or the way that particular drugs or behaviours interact with the motivational system to create a positive feedback cycle rather than the self-correcting systems that normally operate to ensure that no one behaviour receives an unwarranted priority at the expense of others.
For example, with palatable food, our natural processes of satiation and habituation reduce its rewarding value as we eat more of it during a meal. By contrast, with cocaine and amphetamine, reward mechanisms become sensitised to the impulse generating effects of the drug (Berridge & Robinson, 2016). In the case of alcohol dependence, addicts develop craving, rebound anxiety and adverse physical symptoms which provide a very powerful motivation to resume drinking (Seo & Sinha, 2014). In the case of tobacco smoking, rapid ingestion of nicotine leads to strong cravings through multiple mechanisms, including creation of an acquired drive state, similar to hunger, when CNS nicotine concentrations become depleted (West, 2009). So development of general models and theories of addiction will involve bringing together a wide range of constructs and processes relating to canonical motivational theory (i.e. a theory of what normally happens) and how abnormalities in motivation occur. These processes will be both internal and external to individuals, groups and populations.
Diversity in the study of addiction
While there is a need for greater clarity of constructs in the study of addiction, no investigator or organisation has the authority, or expertise, to propose a single unifying conceptual framework.
Figure 1: du Plessis' classification of addiction theories (du Plessis, 2014)
a) Eight major methodologies
b) Types of addiction theory classified according to the eight methodologies
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A general theory of addiction has yet to be developed, but a key requirement for such a theory is that it should recognise and accommodate multiple viewpoints on addiction, and not be limited to a single viewpoint such as the `medical model' (construing addiction in term of a mental disorder, disease or disease process). Figure 1 shows du Plessis' classification of the types of theory that would need to be recognised and accommodated by a general theory of addiction according to eight major methodologies (du Plessis, 2014). Some specific theories and several theoretical approaches have attempted to span a number of the zones in this classification. Of the specific theories, the theory of Excessive Appetites and PRIME Theory have been elaborated in some detail (Orford, 2001; West & Brown, 2013), respectively).
It is important not to overstate this diversity. Despite the complexities discussed earlier, the observed phenomena that are captured by a term like `addiction' are important, and it is useful to give a label to a construct that captures these. Moreover, there are shared understandings of many of the features that characterise addictive drug use, even where there may be disagreement around details and where emphasis should be placed.
On the other hand, it should go without saying that a general theory which achieved greater clarity by simply ignoring this diversity of viewpoints would not in fact be a general theory at all. To move forward, we need a way to achieve clarity of constructs and develop consensus, while at the same time recognising that divergent views have utility.
Addressing the challenge in the Semantic Web
The technology associated with the Semantic Web provides the basis for a response to the challenge we have outlined: a way for the science of addiction to move from its current state of confused, confusing and imprecise terminology to a way of representing addiction and models of addiction that will promote collaborative working, respect and preserve different viewpoints on addiction, but nevertheless allow all research results to be integrated, and theoretical predictions to be tested, and so advance the field.
What is the Semantic Web? One way to answer this question is to chart the development of the Semantic Web from the Worldwide Web (www). The Worldwide Web has revolutionised our lives by making information available from a vast range of sources. It defines a technological framework for locating and exchanging diverse content types ? for example, text, images, and films. At the heart of this framework is the Uniform Resource Locator (URL), a unique `address' for each of the billions of different web pages. These URLs are stored as a code that means nothing to human readers, but a
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