• Addictive substances are highly reinforcing.
• They are reinforcing because they induce pleasure.
• Pleasure leads to ‘liking’ the effects of addictive substances.
• ‘Liking’ a substance can become conditioned to substance-related cues.
• ‘Wanting’ a substance can occur at the expense of ‘liking’ the substance.
• Excessive ‘wanting’ can lead to a loss of control of substance use.
• Substance use habits are unconsciousness—they are automatic.
• Withdrawal from substances of abuse leads to repeated use.
• Craving for substances may occur following prolonged abstinence.
• Craving may trigger substance relapse.
Addiction is characterized by the compulsion to seek and take a substance (or engage in behaviours, such as gambling), the loss of control in limiting substance intake, and the emergence of a negative emotional state (e.g. dysphoria, anxiety) when substance intake is prevented (see Figure 3.1). Elements of addiction during the addiction trajectory are a reflection of changes in brain homeostasis. These homeostatic changes ultimately lead to: (1) a decreased sensitivity for natural rewards; (2) an enhanced sensitivity for conditioned substance cues and the expectation of substance use rewards; (3) a weakened control over substance use urges and substance-taking behaviour; and (4) substance tolerance and withdrawal.
3.1 Key elements of addiction
Whatever the initial reason for substance use in individuals (e.g. reducing discomfort, sensation-seeking), substances of abuse are highly positively reinforcing (i.e. rewarding). They are rewarding, particularly during the initial phases of use, because they induce a conscious experience of pleasure.
This pleasure induces ‘liking’. ‘Liking’ is related to activity in discrete hedonic ‘hot spots’ within the reward circuitry of the brain (see Chapter 4). Activity in these ‘hot spots’ has been shown to be increased in animals, together with ‘liking’ reactions, when they are stimulated. Unconscious (or implicit) ‘liking’ reactions to hedonic stimuli are also possible without the conscious feelings of pleasure. The enhancement of ‘liking’, however, is both restricted and fragile. These ‘liking’ systems are relatively inflexible to activation compared to ‘wanting’ systems (see Wanting).
This ‘liking’ of substance-induced pleasure may, in some individuals, lead to an inflated evaluation of the substance. This exaggerated appraisal of pleasure is likely to positively reinforce the desire to repeat substance use. Similarly, the initial response to a substance that is not liked by an individual, but rather appraised as aversive (i.e. disliked), will be negatively reinforced—the individual will not continue to use (though tobacco is an exception because users have to overcome the unpleasantness of the initial smoking experience in order to benefit from the effects).
As substance use increases, reinforcement can become more pronounced in response to cues associated with the substance (e.g. people, objects, places). These responses to cues can be greater than that produced by the substance itself. Therefore, the ‘liking’ of the pleasurable effects of substances during the initial stages of use is accompanied by the formation of powerful conditioned responses to the substance—cues can trigger the expectation of ensuing pleasure.
Responses to substance cues have also been shown to correlate with the subjective experience of craving in substance dependence. This associative learning, therefore, drives the incessant preoccupation with, and craving of, the substance. This can provoke relapse during abstinence.
3.1.2 Reducing suffering
Many people turn to substance use in order to reduce pain—either physical or psychological—in a form of self-medication. The use of alcohol, for example, to reduce performance anxiety or social anxiety disorder is a form of self-medicating. Social anxiety disorder is a very common disorder and is the most common diagnosable disorder in alcoholism—a quarter of young male alcoholics suffer from this disorder. Other populations find that different drugs can help with their underlying condition. People with ADHD, for example, find that stimulants (e.g. amphetamine) can be helpful. This population often report, following the self-administration of stimulants, that they become more calm, focussed, and less distracted.
Understanding the reasons for drug use is critically important in devising the right treatment for each individual. Patients with social anxiety can respond very well to selective serotonin reuptake inhibitors (SSRIs) whereas those with ADHD require stimulants or atomoxetine. In both these groups, appropriate medical prescribing will reduce their maladaptive alcohol/drug use.
The use of opiates (e.g. morphine) in pain control is often accompanied by fears of becoming addicted. Whilst this can happen, it is relatively rare, and, in most countries, there is a relative under-treatment of pain with these types of drugs because doctors fear the patient may become addicted.
Some substance users explicitly state that they are only fully ‘real’ when under the influence of the substance. Terms, such as ‘it was the missing piece of the jigsaw’ or ‘I felt normal for the first time when I first drank’, suggest that substance use may induce a false sense of psychological security. Such experiences are particularly common in opiate and alcohol addiction and may reflect an underlying genetic propensity or some psychological problem. Nevertheless, the meaning behind substance use makes it difficult for such people to give up, as they never feel fully complete in the absence of the substance.
Substance addiction is a form of long-term memory—particularly for the stimuli associated with the effects of the substance. This issue of conditioned substance use memories is dealt with in Chapter 4.
Substance-induced rewards that a person likes are rewards that the person wants. With repeated and excessive substance use comes an adaptive dampening down of the initial appetitive effects. It is at this point that the development of ‘wanting’, at the expense of pleasure and ‘liking’, begins to emerge. Significantly, the ‘liking’ and ‘wanting’ of rewards are dissociable, both psychologically and biologically. Wanting refers to an incentive salience—a type of incentive motivation that promotes approach towards, and the consumption of, rewards. In the case of substance abuse and addiction, excessive incentive salience may cause irrational wanting due to substance-related cues acquiring increased incentive-motivational value.
This ‘wanting’ for the substance, without ‘liking’ it, is caused by continued and excessive associative learning and a decreased sensitivity of the brain’s reward circuitry to the pleasure-inducing properties of the substance itself. At this point, substances may no longer be liked but rather become compulsively wanted by the user. Importantly, brain regions for ‘wanting’ are more ubiquitous and more easily activated than those for ‘liking’. ‘Wanting’ mechanisms are more numerous and diverse, which may explain the disproportionate ‘wanting’ of a substance reward without equally liking the same reward.
Preoccupation/anticipation or craving in addiction is thought to be a key element of relapse in humans. Research suggests that craving involves complex interactions between numerous neurotransmitter systems in the brain (e.g. dopamine and glutamate). Significantly, craving is not exclusive to the stage of acute substance withdrawal and, indeed, may overcome individuals who are in a protracted period of alcohol or drug abstinence. Craving may be triggered by environmental cues associated with the pleasurable effects of substances—cues that trigger conditioned memories of substance rewards. This may lead to wanting the substance and, consequently, relapse. Craving, however, has proved to be a difficult construct to measure clinically and often does not correlate well with relapse.
Substance addiction is characterized by a discrepancy between the user’s expressed intentions to abstain from the substance and their behaviour, which is characterized by repeated relapses and continued use of the substance. The concept of ‘motivational conflict’ appears fundamental to understanding substance abuse and addiction. Motivational problems involving conflict between inclinations to use (‘approach’) and refrain from (‘avoidance’) the substance are highly relevant to breaking habits that are complicit in sustaining addiction.
There is evidence that substance use habits begin to originate outside of consciousness (i.e. users are unaware). The compulsive sequence of substance use behaviours become so practised that they can be extremely difficult to avoid initiating by the user. The role of implicit (or automatic) cognitive processes in substance use and addiction, where habit occurs outside the realms of consciousness, may be important to treating substance addiction. Automatic cognitive processes related to habit are spontaneous and fast, as opposed to ‘controlled’ cognitive processes, which are deliberate, slow and require conscious awareness. It has been proposed that substance use leads to the development of automatic processes that promote approach behaviour toward substance-related cues and, ultimately, substance use.
Significantly, treatment strategies, during which ‘controlled’ processes are engaged in, to either inhibit or override these automatic approach tendencies, are likely to promote substance avoidance. Therefore, during the emergence of increased substance addiction, an approach-avoidance conflict between such automatic appetitive responses to substance cues and controlled processes will emerge. The emergence of this conflict is thought to exacerbate the preoccupation with substance use in an attempt to bring about its resolution as well as lead to secondary psychiatric issues, such as anxiety and depression.
For many addicts, the initial period of drug use is driven by pleasure. Over time, the motivation to use switches to a desire to minimize withdrawal. Withdrawal usually refers to physiological symptoms experienced upon the abrupt termination of the substance. The response that follows the stage of drug intoxication differs markedly across drugs and is influenced by the chronicity and frequency of its abuse. For some drugs, such as opiates, alcohol, and sedative hypnotics, drug discontinuation in chronic users can trigger an intense, acute physical withdrawal syndrome. If not properly managed, a severe physical withdrawal syndrome can sometimes be fatal.
All drugs of abuse are associated with a motivational withdrawal syndrome characterized by dysphoria, irritability, emotional distress, and sleep disturbances. These symptoms can persist, even after protracted withdrawal.
Acute withdrawal is distinct from protracted or motivational withdrawal, but both contribute to relapse. Both the physical and psychological withdrawal symptoms during acute abstinence involve a process of attempting to achieve a new state of stability (i.e. homeostasis) within endogenous systems responsible for maintaining the internal stability of the organism. Relapse during withdrawal may be a form of negative reinforcement—using substances to minimize the unpleasantness of withdrawal.
References and Further Reading
Barkby H, Dickson JM, Roper L and Field M (2011). To approach or avoid alcohol? Automatic and self-reported motivational tendencies in alcohol dependence. Alcoholism: Clinical and Experimental Research, 36, 361–8.Find this resource:
Berridge KC, Robinson TE and Aldridge JW (2009). Dissecting components of reward: ‘liking’, ‘wanting’, and learning. Current Opinion in Pharmacology, 9, 65–73.Find this resource:
Christiansen P, Cole JC, Goudie AJ and Field M (2012). Components of behavioural impulsivity and automatic cue approach predict unique variance in hazardous drinking. Psychopharmacology (Berl), 219, 501–10.Find this resource:
Goldstein RZ, Woicik PA, Moeller SJ, et al. (2010). Liking and wanting of drug and non-drug rewards in active cocaine users: the STRAP-R questionnaire. Journal of Psychopharmacology, 24, 257–66.Find this resource:
Koob GF and Volkow ND (2010). Neurocircuitry of addiction. Neuropsychopharmacology, 35, 217–38.Find this resource:
Zorick T, Nestor L, Miotto K, et al. (2010). Withdrawal symptoms in abstinent methamphetamine-dependent subjects. Addiction, 105, 1809–18.Find this resource: